is_managed and cluster resource maintenance (HEARTBEAT)

This document (7000553) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 10

Situation

On a cluster it is sometimes necessary or at least desirable to take away the control of a resource from the cluster for maintenance without bringing down the whole cluster. An example would be to update the software for a resource in the cluster or maybe change one IP address. And do this without having to stop the whole cluster.

From the documentation:

/usr/share/heartbeat/crm.dtd

 * is_managed_default (boolean, default=TRUE)
   Unless the resource's definition says otherwise,
   * TRUE : resources will be started, stopped, monitored and moved as necessary/required
   * FALSE : resources will not started if stopped, stopped if started nor have any recurring actions scheduled.

it might seem viable to do this by just setting the attribute "is_managed" to "false" on the affected resource.

This is NOT so!

If there is a monitor operation running on the resource, which is the case in most enviroments, then the resource will be in status "unmanaged" but the monitor will still be done. So as soon as the resource gives anything back to the monitor that triggers the failure, the cluster will act accordingly.

Resolution

The reason is for this is, that the the attribute "is_managed" does not affect the monitor if any part of the cluster is managed.

There is two solutions to set the cluster to maintenance:

1. set the global attribute "is_managed" to false (via GUI or CLI):

this will set all resources to "is_managed" "false". Any resource can now be modified. But during this period of time the cluster will NOT check any resource.

2. set the resource attribute "is_managed" to "false" and set the monitor operation of this resource "on_fail" to "ignore".

After the maintenance all settings have to be reverted to make the cluster functioning again.

Disclaimer

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