[ClusterLabs] Antw: Coming in Pacemaker 1.1.17: start a node in standby
Ulrich.Windl at rz.uni-regensburg.de
Tue Apr 25 02:23:37 EDT 2017
>>> Ken Gaillot <kgaillot at redhat.com> schrieb am 24.04.2017 um 22:08 in Nachricht
<df09e69c-1fe9-4dd7-69dd-f704841cc94d at redhat.com>:
> Hi all,
> Pacemaker 1.1.17 will have a feature that people have occasionally asked
> for in the past: the ability to start a node in standby mode.
> It will be controlled by an environment variable (set in
> /etc/sysconfig/pacemaker, /etc/default/pacemaker, or wherever your
> distro puts them):
> # By default, nodes will join the cluster in an online state when they first
> # start, unless they were previously put into standby mode. If this
> variable is
> # set to "standby" or "online", it will force this node to join in the
> # specified state when starting.
> # (experimental; currently ignored for Pacemaker Remote nodes)
> # PCMK_node_start_state=default
> As described, it will be considered experimental in this release, mainly
> because it doesn't work with Pacemaker Remote nodes yet. However, I
> don't expect any problems using it with cluster nodes.
> Example use cases:
> You want want fenced nodes to automatically start the cluster after a
> reboot, so they contribute to quorum, but not run any resources, so the
> problem can be investigated. You would leave
> PCMK_node_start_state=standby permanently.
I wonder: There is a fencing mode "off" and "reboot". Why not have "reboot_standby" (and "off_standby")? The last one would put the node in standby after it has been restarted manually. Probably not very helpful, but for completeness. The other option I could think of is a "timed standby": The node would not run resources for a specified time. For those who prefer retries that fail over a dead inactive cluster.
> You want to ensure a newly added node joins the cluster without problems
> before allowing it to run resources. You would set this to "standby"
> when deploying the node, and remove the setting once you're satisfied
> with the node, so it can run resources at future reboots.
So it's mainly intended for initially adding a node? What about a node-global "on_failure=block"?
At some point you'l have to try to run resources on your new node, unless it's intended for a quorum-only node. Then failures will cause fencing anyway. Usually modern servers boot slow enough to put the node into standby from the other node before it (the fenced one) rebooted.
> You want a standby setting to last only until the next boot. You would
> set this permanently to "online", and any manual setting of standby mode
> would be overwritten at the next boot.
> Many thanks to developers Alexandra Zhuravleva and Sergey Mishin, who
> contributed this feature as part of a project with EMC.
> Ken Gaillot <kgaillot at redhat.com>
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