ha-manager(1)

HA-MANAGER(1)

Proxmox VE Documentation

HA-MANAGER(1)

NAME

ha-manager - Proxmox VE HA Manager

SYNOPSIS

ha-manager <COMMAND> [ARGS] [OPTIONS]

ha-manager add <sid> [OPTIONS]

Create a new HA resource.

HA resource ID. This consists of a resource type followed by a resource specific name, separated with colon (example: vm:100 / ct:100). For virtual machines and containers, you can simply use the VM or CT id as a shortcut (example: 100).

--auto-rebalance <boolean> (default = 1)

HA resource may be migrated during automatic rebalancing

--comment <string>

Description.

--failback <boolean> (default = 1)

Automatically migrate HA resource to the node with the highest priority according to their node affinity rules, if a node with a higher priority than the current node comes online.

--group <string>

The HA group identifier.

--max_relocate <integer> (0 - N) (default = 1)

Maximal number of resource relocate tries when a resource fails to start.

--max_restart <integer> (0 - N) (default = 1)

Maximal number of tries to restart the resource on a node after its start failed. When reached, the HA manager will try to relocate the resource to an eligible node.

--state <disabled | enabled | ignored | started | stopped> (default = started)

Requested resource state.

--type <ct | vm>

Resource type.

ha-manager config [OPTIONS]

List HA resources.

--type <ct | vm>

Only list resources of specific type

ha-manager crm-command arm-ha

Request re-arming the HA stack after it was disarmed.

ha-manager crm-command disarm-ha <resource-mode>

Request disarming the HA stack, releasing all watchdogs cluster-wide.

<resource-mode>: <freeze | ignore>

Controls how HA managed resources are handled while disarmed. The current state of resources is not affected. freeze: new commands and state changes are not applied. ignore: resources are removed from HA tracking and can be managed as if they were not HA managed.

ha-manager crm-command migrate <sid> <node>

Request resource migration (online) to another node.

Target node.

ha-manager crm-command node-maintenance disable <node>

Change the node-maintenance request state.

The cluster node name.

ha-manager crm-command node-maintenance enable <node>

Change the node-maintenance request state.

The cluster node name.

ha-manager crm-command relocate <sid> <node>

Request resource relocation to another node. This stops the service on the old node, and restarts it on the target node.

Target node.

ha-manager crm-command stop <sid> <timeout>

Request the service to be stopped.

<timeout>: <integer> (0 - N)

Timeout in seconds. If set to 0 a hard stop will be performed.

ha-manager groupadd <group> --nodes <string> [OPTIONS]

Create a new HA group. (deprecated in favor of HA rules)

The HA group identifier.

--comment <string>

Description.

--nodes <node>[:<pri>]{,<node>[:<pri>]}*

List of cluster node names with optional priority.

--nofailback <boolean> (default = 0)

The CRM tries to run services on the node with the highest priority. If a node with higher priority comes online, the CRM migrates the service to that node. Enabling nofailback prevents that behavior.

--restricted <boolean> (default = 0)

Resources bound to restricted groups may only run on nodes defined by the group.

--type <group>

Group type.

ha-manager groupconfig

Get HA groups. (deprecated in favor of HA rules)

ha-manager groupremove <group>

Delete ha group configuration. (deprecated in favor of HA rules)

The HA group identifier.

ha-manager groupset <group> [OPTIONS]

Update ha group configuration. (deprecated in favor of HA rules)

The HA group identifier.

--comment <string>

Description.

--delete <string>

A list of settings you want to delete.

--digest <string>

Prevent changes if current configuration file has a different digest. This can be used to prevent concurrent modifications.

--nodes <node>[:<pri>]{,<node>[:<pri>]}*

List of cluster node names with optional priority.

--nofailback <boolean> (default = 0)

--restricted <boolean> (default = 0)

Resources bound to restricted groups may only run on nodes defined by the group.

ha-manager help [OPTIONS]

Get help about specified command.

--extra-args <array>

Shows help for a specific command

--verbose <boolean>

Verbose output format.

ha-manager migrate

An alias for ha-manager crm-command migrate.

ha-manager relocate

An alias for ha-manager crm-command relocate.

ha-manager remove <sid> [OPTIONS]

Delete resource configuration.

--purge <boolean> (default = 1)

Remove this resource from rules that reference it, deleting the rule if this resource is the only resource in the rule

ha-manager rules add <type> <rule> --resources <string> [OPTIONS]

Create HA rule.

HA rule type.

HA rule identifier.

--comment <string>

HA rule description.

--disable <boolean>

Whether the HA rule is disabled.

--resources <type>:<name>{,<type>:<name>}*

List of HA resource IDs. This consists of a list of resource types followed by a resource specific name separated with a colon (example: vm:100,ct:101).

Conditional options:

[type=node-affinity]

--nodes <node>[:<pri>]{,<node>[:<pri>]}*

List of cluster node names with optional priority.

--strict <boolean> (default = 0)

Describes whether the node affinity rule is strict or non-strict.

[type=resource-affinity]

--affinity <negative | positive>

Describes whether the HA resources are supposed to be kept on the same node (positive), or are supposed to be kept on separate nodes (negative).

ha-manager rules config [OPTIONS] [FORMAT_OPTIONS]

Get HA rules.

--resource <string>

Limit the returned list to rules affecting the specified resource.

--type <node-affinity | resource-affinity>

Limit the returned list to the specified rule type.

ha-manager rules list [OPTIONS] [FORMAT_OPTIONS]

Get HA rules.

--resource <string>

Limit the returned list to rules affecting the specified resource.

--type <node-affinity | resource-affinity>

Limit the returned list to the specified rule type.

ha-manager rules remove <rule>

Delete HA rule.

HA rule identifier.

ha-manager rules set <type> <rule> [OPTIONS]

Update HA rule.

HA rule type.

HA rule identifier.

--comment <string>

HA rule description.

--delete <string>

A list of settings you want to delete.

--digest <string>

Prevent changes if current configuration file has a different digest. This can be used to prevent concurrent modifications.

--disable <boolean>

Whether the HA rule is disabled.

--resources <type>:<name>{,<type>:<name>}*

List of HA resource IDs. This consists of a list of resource types followed by a resource specific name separated with a colon (example: vm:100,ct:101).

Conditional options:

[type=node-affinity]

--nodes <node>[:<pri>]{,<node>[:<pri>]}*

List of cluster node names with optional priority.

--strict <boolean> (default = 0)

Describes whether the node affinity rule is strict or non-strict.

[type=resource-affinity]

--affinity <negative | positive>

Describes whether the HA resources are supposed to be kept on the same node (positive), or are supposed to be kept on separate nodes (negative).

ha-manager set <sid> [OPTIONS]

Update resource configuration.

--auto-rebalance <boolean> (default = 1)

HA resource may be migrated during automatic rebalancing

--comment <string>

Description.

--delete <string>

A list of settings you want to delete.

--digest <string>

Prevent changes if current configuration file has a different digest. This can be used to prevent concurrent modifications.

--failback <boolean> (default = 1)

Automatically migrate HA resource to the node with the highest priority according to their node affinity rules, if a node with a higher priority than the current node comes online.

--group <string>

The HA group identifier.

--max_relocate <integer> (0 - N) (default = 1)

Maximal number of resource relocate tries when a resource fails to start.

--max_restart <integer> (0 - N) (default = 1)

Maximal number of tries to restart the resource on a node after its start failed. When reached, the HA manager will try to relocate the resource to an eligible node.

--state <disabled | enabled | ignored | started | stopped> (default = started)

Requested resource state.

ha-manager status [OPTIONS]

Display HA manager status.

--verbose <boolean> (default = 0)

Verbose output. Include complete CRM and LRM status (JSON).

DESCRIPTION

Our modern society depends heavily on information provided by computers over the network. Mobile devices amplified that dependency, because people can access the network any time from anywhere. If you provide such services, it is very important that they are available most of the time.

We can mathematically define the availability as the ratio of (A), the total time a service is capable of being used during a given interval to (B), the length of the interval. It is normally expressed as a percentage of uptime in a given year.

Table 1. Availability - Downtime per Year

Availability %	Downtime per year
99	3.65 days
99.9	8.76 hours
99.99	52.56 minutes
99.999	5.26 minutes
99.9999	31.5 seconds
99.99999	3.15 seconds

There are several ways to increase availability. The most elegant solution is to rewrite your software, so that you can run it on several hosts at the same time. The software itself needs to have a way to detect errors and do failover. If you only want to serve read-only web pages, then this is relatively simple. However, this is generally complex and sometimes impossible, because you cannot modify the software yourself. The following solutions works without modifying the software:

•Use reliable “server” components

Note
Computer components with the same functionality can have varying reliability numbers, depending on the component quality. Most vendors sell components with higher reliability as “server” components - usually at higher price.

•Eliminate single point of failure (redundant components)

•use an uninterruptible power supply (UPS)

•use redundant power supplies in your servers

•use ECC-RAM

•use redundant network hardware

•use RAID for local storage

•use distributed, redundant storage for VM data

•Reduce downtime

•rapidly accessible administrators (24/7)

•availability of spare parts (other nodes in a Proxmox VE cluster)

•automatic error detection (provided by ha-manager)

•automatic failover (provided by ha-manager)

Virtualization environments like Proxmox VE make it much easier to reach high availability because they remove the “hardware” dependency. They also support the setup and use of redundant storage and network devices, so if one host fails, you can simply start those services on another host within your cluster.

Better still, Proxmox VE provides a software stack called ha-manager, which can do that automatically for you. It is able to automatically detect errors and do automatic failover.

Proxmox VE ha-manager works like an “automated” administrator. First, you configure what resources (VMs, containers, ...) it should manage. Then, ha-manager observes the correct functionality, and handles service failover to another node in case of errors. ha-manager can also handle normal user requests which may start, stop, relocate and migrate a service.

But high availability comes at a price. High quality components are more expensive, and making them redundant doubles the costs at least. Additional spare parts increase costs further. So you should carefully calculate the benefits, and compare with those additional costs.

Tip

Increasing availability from 99% to 99.9% is relatively simple. But increasing availability from 99.9999% to 99.99999% is very hard and costly. ha-manager has typical error detection and failover times of about 2 minutes, so you can get no more than 99.999% availability.

REQUIREMENTS

You must meet the following requirements before you start with HA:

•at least three cluster nodes (to get reliable quorum)

•shared storage for VMs and containers

•hardware redundancy (everywhere)

•use reliable “server” components

Optionally, a hardware watchdog can be used - if not available we fall back to the linux kernel software watchdog (softdog).

RESOURCES

The HA Manager’s primary management unit is called an HA resource (or “HA service”). Currently, an HA resource can be either a Virtual Machine (VM) or a Linux Container (CT).

Each HA resource is uniquely identified by a service ID (sid), which consists of the resource type and a type-specific ID, which is the VMID for VMs and containers. For example, for the VM with VMID 100, the service ID is vm:100.

An HA resource can only run on nodes where all of its dependencies are available. By default, the HA Manager treats every cluster node as eligible. To keep this default, a VM or container should:

•use options that are compatible with all cluster nodes

•use only shared storage that is accessible from all cluster nodes

•use only network interfaces that exist on all cluster nodes

•use only device passthroughs that are present on all cluster nodes

If any of these dependencies is only available on a subset of nodes, restrict the HA resource to that subset with a strict node affinity rule (man ha-manager(1)). The HA Manager then limits placement, recovery, and migration to the rule’s nodes.

MANAGEMENT TASKS

This section provides a short overview of common management tasks. The first step is to enable HA for a resource. This is done by adding the resource to the HA resource configuration. You can do this using the GUI, or simply use the command-line tool, for example:

# ha-manager add vm:100

The HA stack now tries to start the resources and keep them running. Please note that you can configure the “requested” resources state. For example you may want the HA stack to stop the resource:

# ha-manager set vm:100 --state stopped

and start it again later:

# ha-manager set vm:100 --state started

You can also use the normal VM and container management commands. They automatically forward the commands to the HA stack, so

# qm start 100

simply sets the requested state to started. The same applies to qm stop, which sets the requested state to stopped.

Note

The HA stack works fully asynchronous and needs to communicate with other cluster members. Therefore, it takes some seconds until you see the result of such actions.

To view the current HA resource configuration use:

# ha-manager config
vm:100


        state stopped

And you can view the actual HA manager and resource state with:

# ha-manager status
quorum OK
master node1 (active, Wed Nov 23 11:07:23 2016)
lrm elsa (active, Wed Nov 23 11:07:19 2016)
service vm:100 (node1, started)

You can also initiate resource migration to other nodes:

# ha-manager migrate vm:100 node2

This uses online migration and tries to keep the VM running. Online migration needs to transfer all used memory over the network, so it is sometimes faster to stop the VM, then restart it on the new node. This can be done using the relocate command:

# ha-manager relocate vm:100 node2

Finally, you can remove the resource from the HA configuration using the following command:

# ha-manager remove vm:100

By default, this will also remove the resource from any rule that references it and will delete rules that only reference this resource. You can override this behavior using --purge 0.

Note

This does not start or stop the resource.

But all HA related tasks can be done in the GUI, so there is no need to use the command line at all.

HOW IT WORKS

This section provides a detailed description of the Proxmox VE HA manager internals. It describes all involved daemons and how they work together. To provide HA, two daemons run on each node:

pve-ha-lrm

The local resource manager (LRM), which controls the services running on the local node. It reads the requested states for its services from the current manager status file and executes the respective commands.

pve-ha-crm

The cluster resource manager (CRM), which makes the cluster-wide decisions. It sends commands to the LRM, processes the results, and moves resources to other nodes if something fails. The CRM also handles node fencing.

Note

Locks are provided by our distributed configuration file system (pmxcfs). They are used to guarantee that each LRM is active once and working. As an LRM only executes actions when it holds its lock, we can mark a failed node as fenced if we can acquire its lock. This then lets us recover any failed HA services securely without any interference from the now unknown failed node. This all gets supervised by the CRM which currently holds the manager master lock.

Service States

The CRM uses a service state enumeration to record the current service state. This state is displayed on the GUI and can be queried using the ha-manager command-line tool:

# ha-manager status
quorum OK
master elsa (active, Mon Nov 21 07:23:29 2016)
lrm elsa (active, Mon Nov 21 07:23:22 2016)
service ct:100 (elsa, stopped)
service ct:102 (elsa, started)
service vm:501 (elsa, started)

Here is the list of possible states:

stopped

Service is stopped (confirmed by LRM). If the LRM detects a stopped service is still running, it will stop it again.

request_stop

Service should be stopped. The CRM waits for confirmation from the LRM.

stopping

Pending stop request. But the CRM did not get the request so far.

started

Service is active an LRM should start it ASAP if not already running. If the Service fails and is detected to be not running the LRM restarts it (see Start Failure Policy (man ha-manager(1))).

starting

Pending start request. But the CRM has not got any confirmation from the LRM that the service is running.

fence

Wait for node fencing as the service node is not inside the quorate cluster partition (see Fencing (man ha-manager(1))). As soon as node gets fenced successfully the service will be placed into the recovery state.

recovery

Wait for recovery of the service. The HA manager tries to find a new node where the service can run on. This search depends on the list of online and quorate nodes as well as the affinity rules the service is part of, if any. As soon as a new available node is found, the service will be moved there and initially placed into stopped state. If it’s configured to run the new node will do so.

freeze

Do not touch the service state. We use this state while we reboot a node, or when we restart the LRM daemon (see Package Updates (man ha-manager(1))).

ignored

Act as if the service were not managed by HA at all. Useful, when full control over the service is desired temporarily, without removing it from the HA configuration.

migrate

Migrate service (live) to other node.

error

Service is disabled because of LRM errors. Needs manual intervention (see Error Recovery (man ha-manager(1))).

queued

Service is newly added, and the CRM has not seen it so far.

disabled

Service is stopped and marked as disabled

Local Resource Manager

The local resource manager (pve-ha-lrm) is started as a daemon on boot and waits until the HA cluster is quorate and thus cluster-wide locks are working.

It can be in three states:

wait for agent lock

The LRM waits for our exclusive lock. This is also used as idle state if no service is configured.

active

The LRM holds its exclusive lock and has services configured.

lost agent lock

The LRM lost its lock, this means a failure happened and quorum was lost.

After the LRM gets in the active state it reads the manager status file in /etc/pve/ha/manager_status and determines the commands it has to execute for the services it owns. For each command a worker gets started, these workers are running in parallel and are limited to at most 4 by default. This default setting may be changed through the datacenter configuration key max_worker. When finished the worker process gets collected and its result saved for the CRM.

Note

The default value of at most 4 concurrent workers may be unsuited for a specific setup. For example, 4 live migrations may occur at the same time, which can lead to network congestions with slower networks and/or big (memory wise) services. Also, ensure that in the worst case, congestion is at a minimum, even if this means lowering the max_worker value. On the contrary, if you have a particularly powerful, high-end setup you may also want to increase it.

Each command requested by the CRM is uniquely identifiable by a UID. When the worker finishes, its result will be processed and written in the LRM status file /etc/pve/nodes/<nodename>/lrm_status. There the CRM may collect it and let its state machine - respective to the commands output - act on it.

The actions on each service between CRM and LRM are normally always synced. This means that the CRM requests a state uniquely marked by a UID, the LRM then executes this action one time and writes back the result, which is also identifiable by the same UID. This is needed so that the LRM does not execute an outdated command. The only exceptions to this behaviour are the stop and error commands; these two do not depend on the result produced and are executed always in the case of the stopped state and once in the case of the error state.

Note

The HA Stack logs every action it makes. This helps to understand what and also why something happens in the cluster. Here its important to see what both daemons, the LRM and the CRM, did. You may use journalctl -u pve-ha-lrm on the node(s) where the service is and the same command for the pve-ha-crm on the node which is the current master.

Cluster Resource Manager

The cluster resource manager (pve-ha-crm) starts on each node and waits there for the manager lock, which can only be held by one node at a time. The node which successfully acquires the manager lock gets promoted to the CRM master.

It can be in three states:

wait for agent lock

The CRM waits for our exclusive lock. This is also used as idle state if no service is configured

active

The CRM holds its exclusive lock and has services configured

lost agent lock

The CRM lost its lock, this means a failure happened and quorum was lost.

Its main task is to manage the services which are configured to be highly available and try to always enforce the requested state. For example, a service with the requested state started will be started if its not already running. If it crashes it will be automatically started again. Thus the CRM dictates the actions the LRM needs to execute.

When a node leaves the cluster quorum, its state changes to unknown. If the current CRM can then secure the failed node’s lock, the services will be stolen and restarted on another node.

When a cluster member determines that it is no longer in the cluster quorum, the LRM waits for a new quorum to form. Until there is a cluster quorum, the node cannot reset the watchdog. If there are active services on the node, or if the LRM or CRM process is not scheduled or is killed, this will trigger a reboot after the watchdog has timed out (this happens after 60 seconds).

Note that if a node has an active CRM but the LRM is idle, a quorum loss will not trigger a self-fence reset. The reason for this is that all state files and configurations that the CRM accesses are backed up by the clustered configuration file system (man pmxcfs(8)), which becomes read-only upon quorum loss. This means that the CRM only needs to protect itself against its process being scheduled for too long, in which case another CRM could take over unaware of the situation, causing corruption of the HA state. The open watchdog ensures that this cannot happen.

If no service is configured for more than 15 minutes, the CRM automatically returns to the idle state and closes the watchdog completely.

HA SIMULATOR

[IMAGE][1] screenshot/gui-ha-manager-status.png

By using the HA simulator you can test and learn all functionalities of the Proxmox VE HA solutions.

By default, the simulator allows you to watch and test the behaviour of a real-world 3 node cluster with 6 VMs. You can also add or remove additional VMs or Container.

You do not have to setup or configure a real cluster, the HA simulator runs out of the box.

Install with apt:

apt install pve-ha-simulator

You can even install the package on any Debian-based system without any other Proxmox VE packages. For that you will need to download the package and copy it to the system you want to run it on for installation. When you install the package with apt from the local file system it will also resolve the required dependencies for you.

To start the simulator on a remote machine you must have an X11 redirection to your current system.

If you are on a Linux machine you can use:

ssh root@<IPofPVE> -Y

On Windows it works with mobaxterm[2].

After connecting to an existing Proxmox VE with the simulator installed or installing it on your local Debian-based system manually, you can try it out as follows.

First you need to create a working directory where the simulator saves its current state and writes its default config:

mkdir working

Then, simply pass the created directory as a parameter to pve-ha-simulator:

pve-ha-simulator working/

You can then start, stop, migrate the simulated HA services, or even check out what happens on a node failure.

CONFIGURATION

The HA stack is well integrated into the Proxmox VE API. So, for example, HA can be configured via the ha-manager command-line interface, or the Proxmox VE web interface - both interfaces provide an easy way to manage HA. Automation tools can use the API directly.

All HA configuration files are within /etc/pve/ha/, so they get automatically distributed to the cluster nodes, and all nodes share the same HA configuration.

Resources

[IMAGE][1] screenshot/gui-ha-manager-status.png

The resource configuration file /etc/pve/ha/resources.cfg stores the list of resources managed by ha-manager. A resource configuration inside that list looks like this:

<type>: <name>


        <property> <value>


        ...

It starts with a resource type followed by a resource specific name, separated with colon. Together this forms the HA resource ID, which is used by all ha-manager commands to uniquely identify a resource (example: vm:100 or ct:101). The next lines contain additional properties:

auto-rebalance: <boolean> (default = 1)

HA resource may be migrated during automatic rebalancing

comment: <string>

Description.

failback: <boolean> (default = 1)

Automatically migrate HA resource to the node with the highest priority according to their node affinity rules, if a node with a higher priority than the current node comes online.

group: <string>

The HA group identifier.

max_relocate: <integer> (0 - N) (default = 1)

Maximal number of resource relocate tries when a resource fails to start.

max_restart: <integer> (0 - N) (default = 1)

Maximal number of tries to restart the resource on a node after its start failed. When reached, the HA manager will try to relocate the resource to an eligible node.

state: <disabled | enabled | ignored | started | stopped> (default = started)

Requested resource state. The CRM reads this state and acts accordingly. Please note that enabled is just an alias for started.

started

The CRM tries to start the resource. Service state is set to started after successful start. On node failures, or when start fails, it tries to recover the resource. If everything fails, service state it set to error.

stopped

The CRM tries to keep the resource in stopped state, but it still tries to relocate the resources on node failures.

disabled

The CRM tries to put the resource in stopped state, but does not try to relocate the resources on node failures. The main purpose of this state is error recovery, because it is the only way to move a resource out of the error state.

ignored

The resource gets removed from the manager status and so the CRM and the LRM do not touch the resource anymore. All {pve} API calls affecting this resource will be executed, directly bypassing the HA stack. CRM commands will be thrown away while the resource is in this state. The resource will not get relocated on node failures.

Here is a real world example with one VM and one container. As you see, the syntax of those files is really simple, so it is even possible to read or edit those files using your favorite editor:

Configuration Example (/etc/pve/ha/resources.cfg).

vm: 501


    state started


    max_relocate 2
ct: 102


    # Note: use default settings for everything

[IMAGE][3] screenshot/gui-ha-manager-add-resource.png

The above config was generated using the ha-manager command-line tool:

# ha-manager add vm:501 --state started --max_relocate 2
# ha-manager add ct:102

Groups

Note

HA Groups are deprecated and migrated to HA Node Affinity rules since Proxmox VE 9.0.

[IMAGE][4] screenshot/gui-ha-manager-groups-view.png

The HA group configuration file /etc/pve/ha/groups.cfg is used to define groups of cluster nodes. A resource can be restricted to run only on the members of such group. A group configuration look like this:

group: <group>


       nodes <node_list>


       <property> <value>


       ...

comment: <string>

Description.

nodes: <node>[:<pri>]{,<node>[:<pri>]}*

List of cluster node members, where a priority can be given to each node. A resource will run on the available nodes with the highest priority. If there are more nodes in the highest priority class, the resources will get distributed to those nodes. The priorities have a relative meaning only. The higher the number, the higher the priority.

nofailback: <boolean> (default = 0)

restricted: <boolean> (default = 0)

Resources bound to restricted groups may only run on nodes defined by the group. The resource will be placed in the stopped state if no group node member is online. Resources on unrestricted groups may run on any cluster node if all group members are offline, but they will migrate back as soon as a group member comes online. One can implement a preferred node behavior using an unrestricted group with only one member.

[IMAGE][5] screenshot/gui-ha-manager-add-group.png

A common requirement is that a resource should run on a specific node. Usually the resource is able to run on other nodes, so you can define an unrestricted group with a single member:

# ha-manager groupadd prefer_node1 --nodes node1

For bigger clusters, it makes sense to define a more detailed failover behavior. For example, you may want to run a set of services on node1 if possible. If node1 is not available, you want to run them equally split on node2 and node3. If those nodes also fail, the services should run on node4. To achieve this you could set the node list to:

# ha-manager groupadd mygroup1 -nodes "node1:2,node2:1,node3:1,node4"

Another use case is if a resource uses other resources only available on specific nodes, lets say node1 and node2. We need to make sure that HA manager does not use other nodes, so we need to create a restricted group with said nodes:

# ha-manager groupadd mygroup2 -nodes "node1,node2" -restricted

The above commands created the following group configuration file:

Configuration Example (/etc/pve/ha/groups.cfg).

group: prefer_node1


       nodes node1
group: mygroup1


       nodes node2:1,node4,node1:2,node3:1
group: mygroup2


       nodes node2,node1


       restricted 1

The nofailback options is mostly useful to avoid unwanted resource movements during administration tasks. For example, if you need to migrate a service to a node which doesn’t have the highest priority in the group, you need to tell the HA manager not to instantly move this service back by setting the nofailback option.

Another scenario is when a service was fenced and it got recovered to another node. The admin tries to repair the fenced node and brings it up online again to investigate the cause of failure and check if it runs stably again. Setting the nofailback flag prevents the recovered services from moving straight back to the fenced node.

Rules

HA rules are used to put certain constraints on HA-managed resources, which are defined in the HA rules configuration file /etc/pve/ha/rules.cfg.

<type>: <rule>


        resources <resources_list>


        <property> <value>


        ...

comment: <string>

HA rule description.

disable: <boolean>

Whether the HA rule is disabled.

resources: <type>:<name>{,<type>:<name>}*

List of HA resource IDs. This consists of a list of resource types followed by a resource specific name separated with a colon (example: vm:100,ct:101).

Table 2. Available HA Rule Types

HA Rule Type	Description
node-affinity	Places affinity from one or more HA resources to one or more nodes.
resource-affinity	Places affinity between two or more HA resources. The affinity negative specifies that HA resources are to be kept on separate nodes, while the affinity positive specifies that HA resources are to be kept on the same node.

Node Affinity Rules

By default, a HA resource is able to run on any cluster node, but a common requirement is that a HA resource should run on a specific node. That can be implemented by defining a HA node affinity rule to make the HA resource vm:100 prefer the node node1:

# ha-manager rules add node-affinity ha-rule-vm100 --resources vm:100 --nodes node1

By default, node affinity rules are not strict, i.e., if there is none of the specified nodes available, the HA resource can also be moved to other nodes. If, on the other hand, a HA resource must be restricted to the specified nodes, then the node affinity rule must be set to be strict.

In the previous example, the node affinity rule can be modified to restrict the resource vm:100 to be only on node1:

# ha-manager rules set node-affinity ha-rule-vm100 --strict 1

For bigger clusters or specific use cases, it makes sense to define a more detailed failover behavior. For example, the resources vm:200 and ct:300 should run on node1. If node1 becomes unavailable, the resources should be distributed on node2 and node3. If node2 and node3 are also unavailable, the resources should run on node4.

To implement this behavior in a node affinity rule, nodes can be paired with priorities to order the preference for nodes. If two or more nodes have the same priority, the resources can run on any of them. For the above example, node1 gets the highest priority, node2 and node3 get the same priority, and at last node4 gets the lowest priority, which can be omitted to default to 0:

# ha-manager rules add node-affinity priority-cascade \


        --resources vm:200,ct:300 --nodes "node1:2,node2:1,node3:1,node4"

The above commands create the following rules in the rules configuration file:

Node Affinity Rules Configuration Example (/etc/pve/ha/rules.cfg).

node-affinity: ha-rule-vm100


        resources vm:100


        nodes node1


        strict 1
node-affinity: priority-cascade


        resources vm:200,ct:300


        nodes node1:2,node2:1,node3:1,node4

Node Affinity Rule Properties.

nodes: <node>[:<pri>]{,<node>[:<pri>]}*

resources: <type>:<name>{,<type>:<name>}*

List of HA resource IDs. This consists of a list of resource types followed by a resource specific name separated with a colon (example: vm:100,ct:101).

strict: <boolean> (default = 0)

Describes whether the node affinity rule is strict or non-strict.

A non-strict node affinity rule makes resources prefer to be on the defined nodes. If none of the defined nodes are available, the resource may run on any other node.

A strict node affinity rule makes resources be restricted to the defined nodes. If none of the defined nodes are available, the resource will be stopped.

Resource Affinity Rules

Another common requirement is that two or more HA resources should run on either the same node, or should be distributed on separate nodes. These are also commonly called "Affinity/Anti-Affinity constraints".

For example, suppose there is a lot of communication traffic between the HA resources vm:100 and vm:200, for example, a web server communicating with a database server. If those HA resources are on separate nodes, this could potentially result in a higher latency and unnecessary network load. Resource affinity rules with the affinity positive implement the constraint to keep the HA resources on the same node:

# ha-manager rules add resource-affinity keep-together \


    --affinity positive --resources vm:100,vm:200

Note

If there are two or more positive resource affinity rules, which have common HA resources, then these are treated as a single positive resource affinity rule. For example, if the HA resources vm:100 and vm:101 and the HA resources vm:101 and vm:102 are each in a positive resource affinity rule, then it is the same as if vm:100, vm:101 and vm:102 would have been in a single positive resource affinity rule.

Note

If the HA resources of a positive resource affinity rule are currently running on different nodes, the CRS will move the HA resources to the node, where most of them are running already. If there is a tie in the HA resource count, the node whose name appears first in alphabetical order is selected.

However, suppose there are computationally expensive, and/or distributed programs running on the HA resources vm:200 and ct:300, for example, sharded database instances. In that case, running them on the same node could potentially result in pressure on the hardware resources of the node and will slow down the operations of these HA resources. Resource affinity rules with the affinity negative implement the constraint to spread the HA resources on separate nodes:

# ha-manager rules add resource-affinity keep-separate \


    --affinity negative --resources vm:200,ct:300

Other than node affinity rules, resource affinity rules are strict by default, i.e., if the constraints imposed by the resource affinity rules cannot be met for a HA resource, the HA Manager will put the HA resource in recovery state in case of a failover or in error state elsewhere.

The above commands created the following rules in the rules configuration file:

Resource Affinity Rules Configuration Example (/etc/pve/ha/rules.cfg).

resource-affinity: keep-together


        resources vm:100,vm:200


        affinity positive
resource-affinity: keep-separate


        resources vm:200,ct:300


        affinity negative

Interactions between Positive and Negative Resource Affinity Rules.

If there are HA resources in a positive resource affinity rule, which are also part of a negative resource affinity rule, then all the other HA resources in the positive resource affinity rule are in negative affinity with the HA resources of these negative resource affinity rules as well.

For example, if the HA resources vm:100, vm:101, and vm:102 are in a positive resource affinity rule, and vm:100 is in a negative resource affinity rule with the HA resource ct:200, then vm:101 and vm:102 are each in negative resource affinity with ct:200 as well.

Note that if there are two or more HA resources in both a positive and negative resource affinity rule, then those will be disabled as they cause a conflict: Two or more HA resources cannot be kept on the same node and separated on different nodes at the same time. For more information on these cases, see the section about rule conflicts and errors (man ha-manager(1)) below.

Interactions between Node and Positive Resource Affinity Rules.

If there are HA resources in a node affinity rule, which are also part of a positive resource affinity rule, then all the other HA resources in the positive resource affinity rule inherit the node affinity rule as well.

For example, if the HA resources vm:100, vm:101, and vm:102 are in a positive resource affinity rule, and vm:102 is in a node affinity rule, which restricts vm:102 to be only on node3, then vm:100 and vm:101 are restricted to be only on node3 as well.

Please note that if there are two or more HA resources in a positive resource affinity rule and in different node affinity rules, then those rules will cause an error and will be disabled as this is currently not supported. For more information on these cases, see the section about rule conflicts and errors (man ha-manager(1)) below.

Resource Affinity Rule Properties.

affinity: <negative | positive>

Describes whether the HA resources are supposed to be kept on the same node (positive), or are supposed to be kept on separate nodes (negative).

resources: <type>:<name>{,<type>:<name>}*

List of HA resource IDs. This consists of a list of resource types followed by a resource specific name separated with a colon (example: vm:100,ct:101).

Rule Conflicts and Errors

HA rules can impose rather complex constraints on the HA resources. To ensure that a new or modified HA rule does not introduce uncertainty into the HA stack’s CRS scheduler, HA rules are tested for feasibility before these are applied. For any rules that fail these tests, these rules are disabled until the conflicts and errors have been resolved.

Currently, HA rules are checked for the following feasibility tests:

•An HA resource can only be part of a single HA node affinity rule.

•An HA resource affinity rule must have at least two HA resources.

•A negative HA resource affinity rule cannot specify more HA resources than there are nodes in the cluster. Otherwise, the HA resources do not have enough nodes to be separated.

•A positive HA resource affinity rule cannot specify the same two or more HA resources as a negative HA resources affinity rule. That is, two or more HA resources cannot be kept together and separate at the same time.

•An HA resource can only be part of a HA node affinity rule and a HA resource affinity rule at the same time, if the HA node affinity rule has a single priority class.

•The HA resources of a positive HA resource affinity rule can only be part of a single HA node affinity rule at most.

•The HA resources of a negative HA resource affinity rule cannot be restricted to less nodes than HA resources by their node affinity rules. Otherwise, the HA resources do not have enough nodes to be separated.

FENCING

On node failures, fencing ensures that the erroneous node is guaranteed to be offline. This is required to make sure that no resource runs twice when it gets recovered on another node. This is a really important task, because without this, it would not be possible to recover a resource on another node.

If a node did not get fenced, it would be in an unknown state where it may have still access to shared resources. This is really dangerous! Imagine that every network but the storage one broke. Now, while not reachable from the public network, the VM still runs and writes to the shared storage.

If we then simply start up this VM on another node, we would get a dangerous race condition, because we write from both nodes. Such conditions can destroy all VM data and the whole VM could be rendered unusable. The recovery could also fail if the storage protects against multiple mounts.

How Proxmox VE Fences

There are different methods to fence a node, for example, fence devices which cut off the power from the node or disable their communication completely. Those are often quite expensive and bring additional critical components into a system, because if they fail you cannot recover any service.

We thus wanted to integrate a simpler fencing method, which does not require additional external hardware. This can be done using watchdog timers.

Possible Fencing Methods

•external power switches

•isolate nodes by disabling complete network traffic on the switch

•self fencing using watchdog timers

Watchdog timers have been widely used in critical and dependable systems since the beginning of microcontrollers. They are often simple, independent integrated circuits which are used to detect and recover from computer malfunctions.

During normal operation, ha-manager regularly resets the watchdog timer to prevent it from elapsing. If, due to a hardware fault or program error, the computer fails to reset the watchdog, the timer will elapse and trigger a reset of the whole server (reboot).

Recent server motherboards often include such hardware watchdogs, but these need to be configured. If no watchdog is available or configured, we fall back to the Linux Kernel softdog. While still reliable, it is not independent of the servers hardware, and thus has a lower reliability than a hardware watchdog.

Configure Hardware Watchdog

By default, all hardware watchdog modules are blocked for security reasons. They are like a loaded gun if not correctly initialized. To enable a hardware watchdog, you need to specify the module to load in /etc/default/pve-ha-manager, for example:

# select watchdog module (default is softdog)
WATCHDOG_MODULE=iTCO_wdt

This configuration is read by the watchdog-mux service, which loads the specified module at startup.

Recover Fenced Services

After a node failed and its fencing was successful, the CRM tries to move services from the failed node to nodes which are still online.

The selection of the recovery nodes is influenced by the list of currently active nodes, their respective loads depending on the used scheduler, and the affinity rules the service is part of, if any.

First, the CRM builds a set of nodes available to the service. If the service is part of a node affinity rule, the set is reduced to the highest priority nodes in the node affinity rule. If the service is part of a resource affinity rule, the set is further reduced to fulfill their constraints, which is either keeping the service on the same node as some other services or keeping the service on a different node than some other services. Finally, the CRM selects the node with the lowest load according to the used scheduler to minimize the possibility of an overloaded node.

Caution

On node failure, the CRM distributes services to the remaining nodes. This increases the service count on those nodes, and can lead to high load, especially on small clusters. Please design your cluster so that it can handle such worst case scenarios.

Fencing & Watchdog Status

The ha-manager status output includes a fencing entry that shows the CRM watchdog state. Each LRM entry additionally shows its own watchdog state.

armed

The CRM is actively managing services and has its watchdog open. Each node’s LRM also holds a watchdog while it has its agent lock. On quorum loss or daemon failure, the respective watchdog triggers a node reset to ensure safe failover.

standby

The HA stack is ready but no CRM is actively running as master, for example when no HA resources are configured yet or the cluster just started. The CRM watchdog is not open. Fencing automatically transitions to armed once a CRM takes over as master.

disarming

A disarm-ha command was issued. The CRM is freezing or suspending services from tracking and waiting for all LRMs to release their watchdogs. The CRM watchdog is still active during this phase. Each LRM entry’s watchdog status changes to released as it acknowledges the disarm.

disarmed

All watchdogs have been released cluster-wide. No automatic fencing, failover, or recovery takes place. See Disarming HA for Cluster Maintenance (man ha-manager(1)).

Note

The watchdog-mux service keeps the underlying /dev/watchdog device open for its entire lifetime, even when no HA client is connected. This prevents other processes from claiming the device and ensures the HA stack can always re-acquire it. Not all hardware watchdog drivers support magic close, so closing the device could trigger an unintended reset.

START FAILURE POLICY

The start failure policy comes into effect if a service failed to start on a node one or more times. It can be used to configure how often a restart should be triggered on the same node and how often a service should be relocated, so that it has an attempt to be started on another node. The aim of this policy is to circumvent temporary unavailability of shared resources on a specific node. For example, if a shared storage isn’t available on a quorate node anymore, for instance due to network problems, but is still available on other nodes, the relocate policy allows the service to start nonetheless.

There are two service start recover policy settings which can be configured specific for each resource.

max_restart

Maximum number of attempts to restart a failed service on the actual node. The default is set to one.

max_relocate

Maximum number of attempts to relocate the service to a different node. A relocate only happens after the max_restart value is exceeded on the actual node. The default is set to one.

Note

The relocate count state will only reset to zero when the service had at least one successful start. That means if a service is re-started without fixing the error only the restart policy gets repeated.

ERROR RECOVERY

If, after all attempts, the service state could not be recovered, it gets placed in an error state. In this state, the service won’t get touched by the HA stack anymore. The only way out is disabling a service:

# ha-manager set vm:100 --state disabled

This can also be done in the web interface.

To recover from the error state you should do the following:

•bring the resource back into a safe and consistent state (e.g.: kill its process if the service could not be stopped)

•disable the resource to remove the error flag

•fix the error which led to this failures

•after you fixed all errors you may request that the service starts again

PACKAGE UPDATES

When updating the ha-manager, you should do one node after the other, never all at once for various reasons. First, while we test our software thoroughly, a bug affecting your specific setup cannot totally be ruled out. Updating one node after the other and checking the functionality of each node after finishing the update helps to recover from eventual problems, while updating all at once could result in a broken cluster and is generally not good practice.

Also, the Proxmox VE HA stack uses a request acknowledge protocol to perform actions between the cluster and the local resource manager. For restarting, the LRM makes a request to the CRM to freeze all its services. This prevents them from getting touched by the Cluster during the short time the LRM is restarting. After that, the LRM may safely close the watchdog during a restart. Such a restart happens normally during a package update and, as already stated, an active master CRM is needed to acknowledge the requests from the LRM. If this is not the case the update process can take too long which, in the worst case, may result in a reset triggered by the watchdog.

NODE MAINTENANCE

Sometimes it is necessary to perform maintenance on a node, such as replacing hardware or simply installing a new kernel image. This also applies while the HA stack is in use.

The HA stack can support you mainly in two types of maintenance:

•for general shutdowns or reboots, the behavior can be configured, see Shutdown Policy (man ha-manager(1)).

•for maintenance that does not require a shutdown or reboot, or that should not be switched off automatically after only one reboot, you can enable the manual maintenance mode.

Maintenance Mode

You can use the manual maintenance mode to mark the node as unavailable for HA operation, prompting all services managed by HA to migrate to other nodes.

The target nodes for these migrations are selected from the other currently available nodes, and determined by the HA rules configuration and the configured cluster resource scheduler (CRS) mode. During each migration, the original node will be recorded in the HA managers' state, so that the service can be moved back again automatically once the maintenance mode is disabled and the node is back online.

Currently you can enabled or disable the maintenance mode using the ha-manager CLI tool.

Enabling maintenance mode for a node.

# ha-manager crm-command node-maintenance enable NODENAME

This will queue a CRM command, when the manager processes this command it will record the request for maintenance-mode in the manager status. This allows you to submit the command on any node, not just on the one you want to place in, or out of the maintenance mode.

Once the LRM on the respective node picks the command up it will mark itself as unavailable, but still process all migration commands. This means that the LRM self-fencing watchdog will stay active until all active services got moved, and all running workers finished.

Note that the LRM status will read maintenance mode as soon as the LRM picked the requested state up, not only when all services got moved away, this user experience is planned to be improved in the future. For now, you can check for any active HA service left on the node, or watching out for a log line like: pve-ha-lrm[PID]: watchdog closed (disabled) to know when the node finished its transition into the maintenance mode.

Note

The manual maintenance mode is not automatically deleted on node reboot, but only if it is either manually deactivated using the ha-manager CLI or if the manager-status is manually cleared.

Disabling maintenance mode for a node.

# ha-manager crm-command node-maintenance disable NODENAME

The process of disabling the manual maintenance mode is similar to enabling it. Using the ha-manager CLI command shown above will queue a CRM command that, once processed, marks the respective LRM node as available again.

If you deactivate the maintenance mode, all services that were on the node when the maintenance mode was activated will be moved back.

Shutdown Policy

Below you will find a description of the different HA policies for a node shutdown. Currently Conditional is the default due to backward compatibility. Some users may find that Migrate behaves more as expected.

The shutdown policy can be configured in the Web UI (Datacenter → Options → HA Settings), or directly in datacenter.cfg:

ha: shutdown_policy=<value>

Migrate

Once the Local Resource manager (LRM) gets a shutdown request and this policy is enabled, it will mark itself as unavailable for the current HA manager. This triggers a migration of all HA Services currently located on this node. The LRM will try to delay the shutdown process, until all running services get moved away. But, this expects that the running services can be migrated to another node. In other words, the service must not be locally bound, for example by using hardware passthrough. For example, strict node affinity rules tell the HA Manager that the service cannot run outside of the chosen set of nodes. If all of these nodes are unavailable, the shutdown will hang until you manually intervene. Once the shut down node comes back online again, the previously displaced services will be moved back, if they were not already manually migrated in-between.

Note

The watchdog is still active during the migration process on shutdown. If the node loses quorum it will be fenced and the services will be recovered.

If you start a (previously stopped) service on a node which is currently being maintained, the node needs to be fenced to ensure that the service can be moved and started on another available node.

Failover

This mode ensures that all services get stopped, but that they will also be recovered, if the current node is not online soon. It can be useful when doing maintenance on a cluster scale, where live-migrating VMs may not be possible if too many nodes are powered off at a time, but you still want to ensure HA services get recovered and started again as soon as possible.

Freeze

This mode ensures that all services get stopped and frozen, so that they won’t get recovered until the current node is online again.

Conditional

The Conditional shutdown policy automatically detects if a shutdown or a reboot is requested, and changes behaviour accordingly.

Shutdown. A shutdown (poweroff) is usually done if it is planned for the node to stay down for some time. The LRM stops all managed services in this case. This means that other nodes will take over those services afterwards.

Note

Recent hardware has large amounts of memory (RAM). So we stop all resources, then restart them to avoid online migration of all that RAM. If you want to use online migration, you need to invoke that manually before you shutdown the node.

Reboot. Node reboots are initiated with the reboot command. This is usually done after installing a new kernel. Please note that this is different from “shutdown”, because the node immediately starts again.

The LRM tells the CRM that it wants to restart, and waits until the CRM puts all resources into the freeze state (same mechanism is used for Package Updates (man ha-manager(1))). This prevents those resources from being moved to other nodes. Instead, the CRM starts the resources after the reboot on the same node.

Manual Resource Movement

Last but not least, you can also manually move resources to other nodes, before you shutdown or restart a node. The advantage is that you have full control, and you can decide if you want to use online migration or not.

Note

Please do not kill services like pve-ha-crm, pve-ha-lrm or watchdog-mux. They manage and use the watchdog, so this can result in an immediate node reboot or even reset.

DISARMING HA FOR CLUSTER MAINTENANCE

Certain cluster maintenance tasks, such as reconfiguring the network or the cluster communication stack (corosync), can cause temporary quorum loss or network partitions. Normally, HA would interpret this as a node failure and trigger self-fencing, disrupting services unnecessarily.

The disarm mechanism releases all CRM and LRM watchdogs cluster-wide, allowing you to perform such maintenance safely without the risk of nodes being fenced.

Important

While disarmed, HA does not protect your services. Failures during this period are not automatically recovered. Keep the disarm window as short as possible.

Resource Modes. When disarming HA, you must choose a resource mode that controls how HA managed resources are handled while disarmed. The current state of resources is not affected.

freeze

New commands and state changes are not applied. Services stay in their current state, but the HA stack does not react to failures or process new requests. This is the safest choice when you expect all nodes to remain running.

ignore

Resources are suspended from HA tracking and can be managed as if they were not HA managed. This allows you to manually start, stop, or migrate services while HA is disarmed. Use this when you need to manually relocate services during maintenance. When re-arming, the CRM rechecks service locations against the configuration to pick up any manual migrations.

Disarming and Re-Arming. To disarm HA with the desired resource mode:

# ha-manager crm-command disarm-ha freeze

or:

# ha-manager crm-command disarm-ha ignore

To re-arm HA after maintenance is complete:

# ha-manager crm-command arm-ha

You can monitor the current state with:

# ha-manager status

The fencing status line shows the current state of the fencing mechanism (see Fencing Status (man ha-manager(1))), including the CRM and LRM watchdog states.

The Disarm Process. After you request disarm, the following sequence happens:

1.The CRM freezes all services or suspends them from tracking, depending on the chosen resource mode.

2.Each LRM finishes its active workers, then releases its agent lock and watchdog.

3.Once all online LRMs are idle, the CRM releases its own watchdog too.

The CRM keeps the manager lock throughout this process, so it can accept and process the arm-ha command to reverse it.

If any services are currently being fenced, recovered, or migrated, the disarm is deferred until these operations complete. This ensures that services in the middle of a transition do not end up in an inconsistent state.

Nodes Offline During Disarm. If a node is offline when HA is disarmed, its LRM cannot process the disarm request. The CRM proceeds to the disarmed state once all online LRMs have completed their part. The offline node does not block this.

When the offline node comes back online while HA is still disarmed, its LRM picks up the disarm state and releases its watchdog without attempting any service recovery.

When you re-arm HA, any services that were on the offline node are handled according to normal HA recovery rules: they are fenced and recovered if the node is still unreachable, or restarted on the node if it has come back online.

Interaction with Maintenance Mode. If a node is already in maintenance mode when disarm is requested, the maintenance migration continues until all services have been moved away. Once no active services and workers remain, the LRM releases its lock and watchdog as part of the disarm process.

When HA is re-armed, the maintenance mode state is preserved. The node remains in maintenance and services are not moved back until maintenance mode is explicitly disabled.

Caution

While the HA stack is disarmed, no automatic recovery, failover, or fencing takes place. A node failure during this window is not detected or handled by HA. Keep the disarm window as short as possible and ensure that the cluster is in a healthy state before re-arming.

CLUSTER RESOURCE SCHEDULING

The Cluster Resource Scheduler (CRS) is responsible for selecting new node placements for HA resources and keeping HA resources on their allowed nodes.

In every HA Manager round, the scheduler goes through every HA resource and checks whether the HA resource needs any new node placement. This new node placement can be caused by different actions, such as recovering HA resources from a fenced node or a new HA affinity rule. See the section CRS Scheduling Points (man ha-manager(1)) for a more thorough description of which actions the CRS takes for specific changes in the cluster.

CRS Scheduling Mode

[IMAGE][6] screenshot/gui-datacenter-options-crs.png

The CRS scheduling mode controls how the CRS will calculate the usage information for the cluster. This usage information is used as a basis for the scheduling decisions. The CRS mode can be changed in the web interface (Datacenter → Options → Cluster Resource Scheduling). The default mode is basic. The change will take effect starting with the next HA Manager round, which should take no longer than 10 seconds.

Basic Scheduler

The number of active guests on each node is used to choose the best-fitting node for an HA resource.

Static-Load Scheduler

Static usage information from active guests on each node is used to choose the best-fitting node for an HA resource. This includes the configured CPU and memory quotas for the active guests.

Dynamic-Load Scheduler

Dynamic usage information from active guests on each node is used to choose the best-fitting node for an HA resource. This includes the average CPU and memory usage as well as the configured CPU and memory quotas for the active guests.

CRS Scheduling Points

In every HA Manager round, the CRS checks whether any HA resources need a new node placement, which can be caused by any of the following scheduling points:

HA resource recovery (always active)

When a node with active HA resources fails, all its HA resources need to be recovered to other nodes. The CRS algorithm will be used here to balance that recovery over the remaining nodes.

HA rule config changes (always active)

If a rule imposes different constraints on the HA resources, the HA stack will use the CRS algorithm to find a new target node for the HA resources affected by these rules depending on the type of the new rules:

•Node affinity rules: If a node affinity rule is created or HA resources/nodes are added to an existing node affinity rule, the HA stack will use the CRS algorithm to ensure that these HA resources are assigned according to their node and priority constraints.

•Positive resource affinity rules: If a positive resource affinity rule is created or HA resources are added to an existing positive resource affinity rule, the HA stack will use the CRS algorithm to ensure that these HA resources are moved to a common node.

•Negative resource affinity rules: If a negative resource affinity rule is created or HA resources are added to an existing negative resource affinity rule, the HA stack will use the CRS algorithm to ensure that these HA resources are moved to separate nodes.

HA resource rebalance on start (opt-in)

When starting an HA resource with rebalance on start enabled, the CRS will select the node best suited for the HA resource. If the selected node is not the current node, the HA resource will be migrated to the selected node.

For the basic scheduler mode (man ha-manager(1)), the node with the fewest active guests is considered the best-suited node.

For the static-load (man ha-manager(1)) and dynamic-load (man ha-manager(1)) scheduler modes, each node in turn is considered as if the HA resource was already running on it, using CPU and memory usage from the associated guest configuration. Then for each such alternative, CPU and memory usage of all nodes are considered, with memory being weighted much more, because it’s a truly limited resource. For both, CPU and memory, highest usage among nodes (weighted more, as ideally no node should be overcommitted) and average usage of all nodes (to still be able to distinguish in case there already is a more highly committed node) are considered.

This setting can be enabled with the CRS option ha-rebalance-on-start in the web interface under Datacenter → Options → Cluster Resource Scheduling.

Important

For the static-load and dynamic-load scheduler modes, this functionality is still in technology preview. The more HA resources the more possible combinations there are, so it’s currently not recommended to use it if you have thousands of HA resources.

CRS Load Balancer

Important

This feature is still in technology preview.

The utilization of individual cluster nodes can vary greatly depending on where guests are currently running and how much load these exert at any moment. This can cause the node utilizations to become imbalanced over time, where HA resources on one node become bottlenecked due to resource contention, while another node is barely utilized.

The HA Manager’s automatic load balancer can lower the overall cluster imbalance by automatically issuing rebalancing migrations. Currently, these migrations are issued only for HA resources and executed sequentially. Furthermore, these migrations always obey the current HA affinity rules.

Disabling auto-rebalance for an HA resource prevents the resource from being part of automatically issued rebalancing migrations.

Note

Any HA resource with a positive affinity for an HA resource with auto-rebalance disabled won’t be part of rebalancing migrations either.

The automatic load balancing system can be enabled and configured in the web interface under Datacenter → Options → Cluster Resource Scheduling. This allows fine-tuning the various parameters as described in the next paragraph for different cluster setups and requirements. The load balancer requires either the static-load (man ha-manager(1)) or dynamic-load (man ha-manager(1)) scheduler mode to be in use.

In every HA Manager round, each of which lasts around 10 seconds, the automatic load balancer checks whether the cluster imbalance exceeds the imbalance threshold. If the cluster imbalance stays above the threshold for at least as many consecutive HA Manager rounds as the hold duration, then the load balancer will select the rebalancing migration for an HA resource, which lowers the overall cluster imbalance the most. The method used to select the best rebalancing migration can be set with the rebalancing method option. Finally, if the selected migration reduces the current cluster imbalance by at least the percentage given by the imbalance improvement option, the load balancer issues the selected migration.

The cluster imbalance is derived from the standard deviation and mean of the individual node loads and is normalized to a 0-100% range. Both the imbalance threshold and the imbalance improvement are configured in percent. The imbalance threshold defaults to 30% and controls the sensitivity of the load balancer; with a value of 0 it will try to select a rebalancing migration every time the hold duration is exceeded. The imbalance improvement defaults to 10% and filters what constitutes an acceptable rebalancing migration; with a value of 0 it will always commit to a migration even if the expected imbalance does not change at all. The value can never be negative, so the balancer will never commit to a migration with an expected imbalance worse than the current one.

Note

It is planned that load balancing will also include non-HA resources in the future.

COPYRIGHT AND DISCLAIMER

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License along with this program. If not, see https://www.gnu.org/licenses/

AUTHOR

Proxmox Server Solutions Gmbh
www.proxmox.com

NOTES

1.: [set $man.base.url.for.relative.links]/images/screenshot/gui-ha-manager-status.png
2.: mobaxterm

https://mobaxterm.mobatek.net/

3.: [set $man.base.url.for.relative.links]/images/screenshot/gui-ha-manager-add-resource.png
4.: [set $man.base.url.for.relative.links]/images/screenshot/gui-ha-manager-groups-view.png
5.: [set $man.base.url.for.relative.links]/images/screenshot/gui-ha-manager-add-group.png
6.: [set $man.base.url.for.relative.links]/images/screenshot/gui-datacenter-options-crs.png

Wed Jun 10 01:54:31 UTC 2026

9.2.2