# Managing Primary/Secondary relationship in cluster **URL:** \ **Category:** Ansible Project\ **Created:** [November 4, 2014, 11:59am UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684 "2014-11-04T11:59:15Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Barry\_Morrison](https://avatars.discourse-cdn.com/v4/letter/b/3bc359/32.png) [@Barry\_Morrison](https://forum.ansible.com/u/Barry_Morrison)\ **Post date:** [November 4, 2014, 11:59am UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684/1 "2014-11-04T11:59:15Z")
I have a pair of servers (server1..domain, server2..domain) in two environments (staging and production). Server1 is primary, server2 is secondary. When I originally built the playbook, I had aliases in the inventory file [staging-cluster] primary server1.staging.domain secondary server2.staging.domain And I’d target the IP of the other host with {{ hostvars[‘primary’][‘ansible\_eth0’][‘ipv4’][‘address’] }} to get the of the “other” host. This worked fine, until I needed the playbook to target another set of hosts in production: [production-cluster] primary server1.prod.domain secondary server2.prod.domain The problem with the above, aliases are global and you can’t have more than one in an inventory. So…this breaks the above lookup {{ hostvars[‘secondary’][‘ansible\_eth0’][‘ipv4’][‘address’] }} As much as I disliked the idea, I then thought to leverage hostvars/serverX.environment.domain with a var like: primary: true partner: server2.environment.domain The above var would exist on server1 since it is the primary and it’s partner is server2 The problem with the above is, I can’t expand {{ partner }} in the above fact (may not have explained that properly, I can’t do this: {{ hostvars[‘{{ partner }}’][‘ansible\_eth0’][‘ipv4’][‘address’] }} or this {{ hostavars[{{partner}}][‘ansible\_eth0’][‘ipv4’][‘address’] }} Anyone have any ideas on how I can manage a primary/secondary role/membership in a cluster? Actually defining if the host is primary/secondary is the easy part…but defining it’s partner and getting facts from its partner, I’m not certain of. Thanks!! ---
**Author:** ![James\_Martin1](https://avatars.discourse-cdn.com/v4/letter/j/0ea827/32.png) [@James\_Martin1](https://forum.ansible.com/u/James_Martin1)\ **Post date:** [November 4, 2014, 2:08pm UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684/2 "2014-11-04T14:08:23Z")
If you wanted to get the ip address of the first node in the production-cluster, you could do something like this. Think of the group as a list and 0 being the first element in the list. `"{{ hostvars[groups['production-cluster'][0]]['ansible_eth0']['ipv4']['address'] }}"` as far as your second example goes, you have some syntax errors in defining your variable. You don’t need to encapsulate “partner” in curly brackets or quotes. The following should work: `{{ hostvars[partner]['ansible_eth0']['ipv4']['address'] }}` - James ---
**Author:** ![Barry\_Morrison](https://avatars.discourse-cdn.com/v4/letter/b/3bc359/32.png) [@Barry\_Morrison](https://forum.ansible.com/u/Barry_Morrison)\ **Post date:** [November 4, 2014, 10:06pm UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684/3 "2014-11-04T22:06:45Z")
{{ hostvars[partner][‘ansible\_eth0’][‘ipv4’][‘address’] }} \<\< doesn’t work “{‘msg’: “AnsibleUndefinedVariable: One or more undefined variables: ‘partner’ is undefined”, ‘failed’: True}” in inventory/host\_vars/server1.domain there is ‘partner: server2.domain’ ---
**Author:** ![James\_Martin1](https://avatars.discourse-cdn.com/v4/letter/j/0ea827/32.png) [@James\_Martin1](https://forum.ansible.com/u/James_Martin1)\ **Post date:** [November 4, 2014, 10:15pm UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684/4 "2014-11-04T22:15:51Z")
That indicates you haven’t defined “partner” properly. Make sure it’s listed in the right pace in your inventory host\_vars. ---
**Author:** ![James\_Martin1](https://avatars.discourse-cdn.com/v4/letter/j/0ea827/32.png) [@James\_Martin1](https://forum.ansible.com/u/James_Martin1)\ **Post date:** [November 4, 2014, 10:17pm UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684/5 "2014-11-04T22:17:34Z")
Ah, I didn’t see that last line. Do a: - debug: var=partner Just to make sure you have your variables loading properly. ---
**Author:** ![Barry\_Morrison](https://avatars.discourse-cdn.com/v4/letter/b/3bc359/32.png) [@Barry\_Morrison](https://forum.ansible.com/u/Barry_Morrison)\ **Post date:** [November 4, 2014, 10:29pm UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684/6 "2014-11-04T22:29:36Z")
I had the remnants of the aliases so host\_vars/server1 didn’t match ‘primary’ I’m not getting the var. Thanks! ---
**Author:** ![shirou](https://avatars.discourse-cdn.com/v4/letter/s/ea5d25/32.png) [@shirou](https://forum.ansible.com/u/shirou)\ **Post date:** [November 5, 2014, 1:34am UTC](https://forum.ansible.com/t/managing-primary-secondary-relationship-in-cluster/16684/7 "2014-11-05T01:34:32Z")
Another way is 'differenct'. (see [http://docs.ansible.com/playbooks\_variables.html#set-theory-filters](http://docs.ansible.com/playbooks_variables.html#set-theory-filters))     - debug: msg="{{ (groups['pair'] | difference(inventory\_hostname))[0] }}" The result is list, not a value. So it requires [0] to get actual hostname. It works if there are more hosts.