[ClusterLabs] best practice for scripting

Tomas Jelinek tojeline at redhat.com
Tue Apr 13 08:21:33 EDT 2021


You can use 'pcs cluster cib' for pacemaker configuration and 'pcs 
cluster status xml' for pacemaker status. Both commands basically just 
pass xml obtained from pacemaker, though. As far as I know, corosync 
also provides parsable output, take a look at corosync-cmapctl. I'm not 
sure about other cluster components.

Be aware that 'pcs status xml' may change in a near future. The reason 
for that is that the xml produced by pacemaker is also changing as a 
part of an effort to provide standardized xml output from most of (or 
all) pacemaker tools.

As far as pcs text output changes: Yes, they are happening. Sometimes 
it's a result of a change in another cluster component (e.g. 'pcs 
status' prints text output from crm_mon). In other cases, it's due to 
adding features, fixing bugs, standardizing output format, etc. It's not 
always possible to avoid the changes.

As we are aware of the difficulties of using pcs in scripts, we indeed 
have a long term goal to provide machine readable output from pcs. Since 
pcs started with a focus on producing human readable output, it's a lot 
of work to do. Quite a big part of pcs code base cannot be easily 
switched to producing machine parsable output. We are slowly moving 
towards it (which in some cases may cause text output changes due to 
code reuse), but it is currently not seen as something to be finished in 
a year.


Dne 13. 04. 21 v 9:17 d tbsky napsal(a):
> Hi:
>      I have some scripts which use 'pcs' and 'crm_mon'. I prefer pcs
> since it is an all-in-one tool. but besides 'pcs cluster cib' it has
> no stable text output. reading document of pacemaker 2.1 I found it
> says:
> "In addition to crm_mon and stonith_admin, the crmadmin, crm_resource,
> crm_simulate, and crm_verify commands now support the --output-as and
> --output-to options, including XML output (which scripts and
> higher-level tools are strongly recommended to use instead of trying
> to parse the text output, which may change from release to release)."
> so if I need to parse the command output, I think I should study these
> commands instead of pcs in the future?  RedHat is doing great job to
> maintain the 'pcs' output consistency between minor versions (eg:
> 7.2-> 7.3). but with major version 7->8 many things changed. if there
> is a more stable method for scripting I would like to follow it.
> thanks a lot for help!
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