Run task only if server belong to some group.

[Marcin Prączko]

Hi,

I have question whether is possible to run task only if server belong to specific group?

--- Quick scenario ---
Lets say that on Inventory I have:
[targets]
srv01
srv02

[webservers]
srv01

Now I would like to play 'common' roles with tasks following (pseudo code):
- name: Do something
  action: Ansible - action
  when: server is in webservers group.

I know that is possible run another play which runs only on webserves but not quite sure whether this suits to my issue:
--- Long scenario ---
I have to cofigure a lot servers belongs to specific groups (web servers / db servers) and munin plugins have some common plugins / and depends of group (www / db).
- When one is installing munin-node from RPM (RH based systems) a lot of munin-plugins are created:
- Now common role from ansible - removes not requried plugins - restarting munin-node
- Then some additional plugins should be configured for server belongs to group www/db

Do I would like to avoid situation that: Common plugin removes not required plugins from munin-node (including those for www - like apache), and then another play install this back.
I woud really achive somethign like that:
- name: Remove not required munin plugins
  action:
  when: Server not belong to group WWW

 ....
- name: Add plugins for WWW
  action:
  when: Server belong to group WWW


I look forward to hearing from you.
Best regards.

[benno joy]

Hi Marcin,

You could do 

when: 'webserver' in group_names

This would make the task run if the current host belongs to webserver group.

when: 'webserver' not in group_names

would run the task if the current host is not on the webserver group.

Hope this helps.

Regards,

Benno

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[Michael DeHaan]

"I know that is possible run another play which runs only on webserves but not quite sure whether this suits to my issue:"

Actually, it does.

hosts: maingroup:&othergroup

Means "all hosts in maingroup that are also in othergroup"  (maingroup:othergroup would be an "OR")

This is cleaner than the when statement and will produce better output, because it won't show 'skipped' for all the other tasks.

--

Michael DeHaan <mic...@ansibleworks.com>
CTO, AnsibleWorks, Inc.
http://www.ansibleworks.com/

[Marcin Prączko]

Hi,

Thank you for help.
Both answers are great:
1. Is really nice that ansible supports condition for task based on this whether server belong to group or not.
2. And I agree that is nicer to split tasks on seperate roles to avoid a lot of 'skipped' tasks.

One more time - thank you for help.

[Marcin Prączko]

Hi,

Are you sure that this is working - just tested on ansible 1.3 and I have error:

ERROR: Syntax Error while loading YAML script, /src/ansible/roles/mysql-munin/tasks/main.yml
Note: The error may actually appear before this position: line 34, column 27

    - mysql_seconds_behind_master
  when: 'dbslave' in group_names
                  ^

I created special role: mysql-munin
There are 3 tasks which should be run - 2 of them on DB master - 1 on DB slave.
But so far I am struggeling to run task only on server which belongs to specific group.

Tasks list:
  play #3 (Database | Configurtion for database servers):
    MySQL-munin | Create Munin configuration - Template    # Should run on DB servers
    MySQL-munin | Link Official munin plugins    # Should run on DB servers
    MySQL-munin | Link Custom munin plugins  # Should run ONLY on Slave DB server

Task: #3
- name: MySQL-munin | Link Custom munin plugins
  file: src=/opt/munin/lib/plugins/{{ item }}
        dest=/etc/munin/plugins/{{ item }}
        state=link
  with_items:
    - mysql_seconds_behind_master
  notify:
    - restart munin-node
  tags:
    - munin_conf_plugin_mysql
# Adding this line
  when: 'dbslave' in group_names
- breaks formating for yaml
- Displaying error which I've described above.

Best regards,
Marcin Praczko

[Michael DeHaan]

Yep, as this says, this is a YAML syntax error.

Since you started the line with a quote, YAML was expecting the whole line to be quoted.

This can be fixed by changing

  when: 'dbslave' in group_names

To:

  when: "'dbslave' in group_names"

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[Marcin Prączko]

Hi Michael,

This is working now as expected - thank you very much for help.

Marcin

[Dhruvin Shah]

Surprisingly simple and powerful.

It works like a charm. Thanks Michael and everyone.