How to check a hosts group membership in Ansible

Written by - 0 comments

Published on - Listed in Ansible Linux


While playing around with group_vars, I noticed that a specific host never applied these group_vars.

Multiple PHP settings were defined in a group_vars:

ck@ansible:~$ cat /pub/ansible/inventory/group_vars/php_small.yaml
php:
  fpm:
    pool:
      pm.max_children: 25
      pm.start_servers: 2
      php_admin_value[apc.shm_size]: 128M
      php_admin_value[opcache.memory_consumption]: 128
      php_admin_value[opcache.max_accelerated_files]: 32531

In the host inventory, the target host (webserver11) is listed under this group name "php_small":

ck@ansible:~$ cat /pub/ansible/inventory/containers
[...]
[php]
:children php_small

[php_small]
webserver11 ansible_ssh_host=10.10.55.1

So I would have assumed that these PHP settings for the group php_small are applied. But when I ran the playbook, the following error showed up:

TASK [PHP - Test host_vars] ******************************************************************************************
fatal: [webserver11]: FAILED! => {"msg": "Unable to look up a name or access an attribute in template string ({{ php.fpm.pool | dict2items }}).\nMake sure your variable name does not contain invalid characters like '-': dict2items requires a dictionary, got <class 'ansible.template.AnsibleUndefined'> instead."}

Meaning: The php.fpm.pool dictionary was not found.

Check group membership of a host with playbook

To verify, that the webserver11 host is REALLY a member of the php_small group, you can add the following debug message as an early task into a playbook:

ck@ansible:~$ cat /pub/ansible/playbooks/group_membership.yaml
---
- name: ANSIBLE - Check group membership - Infiniroot LLC  
  hosts: '{{ target }}'
  tasks:

  - debug:
      msg: "{{ group_names }}"
    ignore_errors: True

When this playbook is run, the group_names (which is an array and can show multiple groups) are shown:

TASK [debug] **************************************************************
ok: [webserver11] => {
    "msg": [
        "webservers"
    ]
}

The output clearly shows that this host (webserver11) is member of the group "webserver", but not of php_small. No wonder my PHP settings are not applied.

Syntax error in inventory is the cause

It turns out to be an error in my inventory file. The group parent/child relationships need to be defined with another syntax as I used above:

ck@ansible:~$ cat /pub/ansible/inventory/containers
[...]
[php:children]
php_small


[php_small]
webserver11 ansible_ssh_host=10.10.55.1

After fixing the inventory file, the group_membership playbook now shows the following groups:

ck@ansible:~$ ansible-playbook /pub/ansible/playbooks/group_membership.yaml --extra-vars="target=webserver11"
[...]
TASK [debug] **************************************************************
ok: [webserver11] => {
    "msg": [
        "webservers",
        "php",
        "php_small"
    ]
}

Mystery solved!

Alternative: Check group membership with ansible-inventory

As a reply to my Toot, Kevin Honka mentioned the possibility to use ansible-inventory. Indeed, the command can be used to do a group listing and nicely presents all the servers present in a group:

ck@ansible:~$ ansible-inventory --graph
[...]
  |--@php:
  |  |--@php_large:
  |  |  |--webserver10
  |  |--@php_small:
  |  |  |--webserver11
  |  |  |--webserver12

Thanks for the hint!


Add a comment

Show form to leave a comment

Comments (newest first)

No comments yet.

RSS feed

Blog Tags:

  AWS   Android   Ansible   Apache   Apple   Atlassian   BSD   Backup   Bash   Bluecoat   CMS   Chef   Cloud   Coding   Consul   Containers   CouchDB   DB   DNS   Database   Databases   Docker   ELK   Elasticsearch   Filebeat   FreeBSD   Galera   Git   GlusterFS   Grafana   Graphics   HAProxy   HTML   Hacks   Hardware   Icinga   Influx   Internet   Java   KVM   Kibana   Kodi   Kubernetes   LVM   LXC   Linux   Logstash   Mac   Macintosh   Mail   MariaDB   Minio   MongoDB   Monitoring   Multimedia   MySQL   NFS   Nagios   Network   Nginx   OSSEC   OTRS   Office   PGSQL   PHP   Perl   Personal   PostgreSQL   Postgres   PowerDNS   Proxmox   Proxy   Python   Rancher   Rant   Redis   Roundcube   SSL   Samba   Seafile   Security   Shell   SmartOS   Solaris   Surveillance   Systemd   TLS   Tomcat   Ubuntu   Unix   VMWare   VMware   Varnish   Virtualization   Windows   Wireless   Wordpress   Wyse   ZFS   Zoneminder