[ClusterLabs Developers] [crmsh] configuration management modules api crmsh#90

[Enno Gröper]

Hi,
I'm currently deploying some clusters using Ansible configuration 
management tool.
Unfortunately I didn't find anything "nice" to configure a pacemaker 
cluster using Ansible.
There are some hacks involving, to my knowledge, a reload of the whole 
cib on every change, but this would mean to restart all resources, even 
if I'm changing only a small part of the pacemaker config (if I 
understand that correctly).
And there exists a rudimentary python module ansible-pacemaker [1] (and 
some improvements to it spread in forks), which works fine for simple 
cases, but doesn't support some basic features (like usual location rules).
It uses crm commands to query the cluster and make changes to individual 
resources and uses its own parsers to read the config and to compare new 
and old directives / detect changes (see below).

In my opinion such a module (doesn't matter whether it's for Ansible, 
Chef, puppet or whatever) needs to achieve the following:
* detect if a defined setting/resource is already there and configured 
identically (no change necessary)
* on changes: change cluster config with minimal impact to 
other/unrelated resources

To achieve the first goal I thought about simply using the parser of 
crmsh instead of writing separate ones. The questions then is how to 
detect changes. It seems like crmsh.xmlutil.xml_equals would be a good 
fit, since the crmsh parser returns xml.

The open question is how to make the changes.
We could simply run "crm configure" or "crm configure delete", but that 
way we have unwanted side effects.

In my example I have two ips in a resource group and a location rule for 
that group, that prefers a specific node.
Due to a bug in ansible-pacemaker both ips get changed everytime (don't 
know why yet). Because changes are made in a delete & insert cycle this 
results in the resource group getting removed everytime, till the group 
resource itself gets updated (reinserted) through ansible-pacemaker.
Because of that the location constraint gets removed (by crm) and 
reinserted (by the ansible-module) on every run of the ansible playbook.


Do you have an idea how to improve that? Is there some api configuration 
management modules could use?
I thought about using CibFactory and _replace_cib or _patch_cib directly 
or looking at how "crm configure edit" applies the changes done in the 
editor.
How to apply the changes with minimal impact?

[1] https://github.com/yosshy/ansible-pacemaker


Best regards,
Enno

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