Complex host patterns

Archives Ansible Project
1

Hi All

When working with host patterns, is it possible to craft one that says “must be in group X and must be in either group Y, W and Z”?

e.g. host must be in group “webserver” but it must also be in either group dc1, dc2 or dc3.

I can see how to check that webserver is part of dc1 (webserver,&dc1) but not sure how to build it with multiple “OR” on the “AND” (something like “webserver,&(dc1,dc2,dc3)” is what I’m looking for but it doesn’t work)

Cheers
Gonz

2

There is an example in the doc (you posted the link).

webservers:dbservers:&staging
The above configuration means “all machines in the groups ‘webservers’ and ‘dbservers’ are to be managed if they are in the group ‘staging’ also, …

3

Not quite. How about “all machines in the groups webservers and dbservers are to be managed only if they are part of staging OR qa”?

4

Put the dc1, dc2 and dc3 group in a group called dc and then you can use

  webserver:&dc

5

You’re trying to do it backwards. Build the union of your other groups and do the intersection with webserver.

&webserver,dc1,dc2,dc3

6

Thanks, good suggestion. I suppose there’s no way to say “must be webserver OR dbserver AND in (dc1 OR dc2 OR dc3)”?

  • Gonz
7

I’d like to be able to do this on the fly so creating a custom group like that is not ideal.

  • Gonz
8

Not in a host pattern. no. If you can’t do it in the inventory, you can do it with a dynamic group:

`

  • hosts: localhost
    gather_facts: false
    tasks:

  • add_host:
    name: “{{ item }}”
    groups: target_hosts
    when: hostvars[item].group_names | intersect([‘dc1’, ‘dc2’, ‘dc3’])
    loop: “{{ groups.webserver | union(groups.dbserver) }}”

  • hosts: target_hosts
    tasks:

  • command: /bin/true

`

9

Thanks for that! Very useful.

  • Gonz