Can SBD fencing be used only for some of the nodes within same cluster?

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux Server 8 (with the High Availability Add On)
  • SBD fencing

Issue

Previously, to use a watchdog-only SBD configuration, all nodes in the cluster had to use SBD. That prevented using SBD in a cluster where some nodes support it but other nodes (often remote nodes) required some other form of fencing.

Resolution

As of pacemaker-2.1.0-8.el8 and later users can configure a watchdog-only SBD setup using the new fence_watchdog agent, which allows cluster configurations where only some nodes (cluster nodes) use watchdog-only SBD for fencing and other nodes (remote nodes) use other fencing types. A cluster may only have a single such device, and it must be named watchdog.

fence_watchdog just provides meta-data - actual fencing is done by the pacemaker internal watchdog agent.

Root Cause

To use a watchdog-only SBD configuration, all nodes in the cluster had to use SBD. That prevented using SBD in a cluster where some nodes support it but other nodes (often remote nodes) required some other form of fencing.

Diagnostic Steps

fence_watchdog supports following parameters:

# pcs stonith describe fence_watchdog
.
.
.
    Stonith options:
      nodename: Ignored
      plug: Ignored
      pcmk_host_map: A mapping of host names to ports numbers for devices that do not support host names. Eg.
                     node1:1;node2:2,3 would tell the cluster to use port 1 for node1 and ports 2 and 3 for node2
      pcmk_host_list: A list of machines controlled by this device (Optional unless pcmk_host_check=static-list).
      pcmk_host_check: How to determine which machines are controlled by the device. Allowed values: dynamic-list (query
                       the device via the 'list' command), static-list (check the pcmk_host_list attribute), status (query
                       the device via the 'status' command), none (assume every device can fence every machine)
      pcmk_delay_max: Enable a delay of no more than the time specified before executing fencing actions. Pacemaker
                      derives the overall delay by taking the value of pcmk_delay_base and adding a random delay value
                      such that the sum is kept below this maximum. This prevents double fencing when using slow devices
                      such as sbd. Use this to enable a random delay for fencing actions. The overall delay is derived
                      from this random delay value adding a static delay so that the sum is kept below the maximum delay.
      pcmk_delay_base: Enable a base delay for fencing actions and specify base delay value. This prevents double fencing
                       when different delays are configured on the nodes. Use this to enable a static delay for fencing
                       actions. The overall delay is derived from a random delay value adding this static delay so that
                       the sum is kept below the maximum delay.
      pcmk_action_limit: The maximum number of actions can be performed in parallel on this device Cluster property
                         concurrent-fencing=true needs to be configured first. Then use this to specify the maximum number
                         of actions can be performed in parallel on this device. -1 is unlimited.
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