Novell LINUX ENTERPRISE 11 - HIGH AVAILABILITY, Manual, Page: 77 / 298

crm(live)configure# order rsc1 rsc2
crm(live)configure# colocation rsc2 rsc1
It is only possible to set a score of INFINITY or -INFINITY, defining resources
that must always or must never run on the same node. For example, to run the two re-
sources with the IDs
filesystem_resource
and
nfs_group
always on the same
host, use the following constraint:
crm(live)configure# colocation nfs_on_filesystem inf: nfs_group
filesystem_resource
For a master slave configuration, it is necessary to know if the current node is a master
in addition to running the resource locally. This can be checked with an additional
to_role
or
from_role
attribute.
5.5.3 Ordering Constraints
Sometimes it is necessary to provide an order in which services must start. For example,
you cannot mount a file system before the device is available to a system. Ordering
constraints can be used to start or stop a service right before or after a different resource
meets a special condition, such as being started, stopped, or promoted to master. Use
the following commands in the
crm
shell to configure an an ordering constraint:
crm(live)configure# order nfs_after_filesystem mandatory: group_nfs
filesystem_resource
5.5.4 Constraints for the Example
Configuration
The example used for this chapter would not work as expected without additional con-
straints. It is essential that all resources run on the same machine as the master of the
drbd resource. Another thing that is critical is that the drbd resource must be master
before any other resource starts. Trying to mount the drbd device when drbd is not
master simply fails. The constraints that must be fulfilled look like the following:
• The file system must always be on the same node as the master of the drbd resource.
crm(live)configure# colocation filesystem_on_master inf: \
filesystem_resource drbd_resource:Master
Configuring Cluster Resources From Command Line 67