Run task only if server belong to some group.

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1

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.

2

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

3

“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.

4

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.

5

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

6

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”

7

Hi Michael,

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

Marcin

8

Surprisingly simple and powerful.
It works like a charm. Thanks Michael and everyone.