Use host var in a task in when clause

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1

Hey All,

I’m trying to force a task to run based on a host variable I’ve set. The goal is to only have the task run (on a host) when the “elasticsearch_purge_old_indices_node” variable is set to “yes”.

Inventory file:

[elasticsearch]
elasticsearch1 elasticsearch_purge_old_indices_node=yes
elasticsearch2

elasticsearch3

Task:

  • name: add a nightly cronjob task to purge node
    lineinfile: dest=/etc/crontab line=“0 1 * * * * root /path/to/script.sh” state=present
    when: elasticsearch_purge_old_indices_node == “yes”

Error output:

TASK: [elasticsearch | cron job to purge old log indices] **************
fatal: [elasticsearch1] => One or more undefined variables: ‘dict object’ has no attribute ‘address’
fatal: [elasticsearch2] => error while evaluating conditional: elasticsearch_purge_old_indices_node == “yes”
fatal: [elasticsearch3] => error while evaluating conditional: elasticsearch_purge_old_indices_node == “yes”

How do I force a task to run based on a host variable I’ve set?

Thanks!

2

Hi Michael

Ansible considers “yes” strings as True booleans but for comparison you can use the bool filter. Perhaps try something like this:

- debug: msg="run this task"
  when: elasticsearch_purge_old_indices_node|bool
3

Thanks for your help Tom.

So, in this situation there is actually no difference between…

elasticsearch_purge_old_indices_node|bool
AND
elasticsearch_purge_old_indices_node == “yes”

The error: “One or more undefined variables: ‘dict object’ has no attribute ‘address’” is a misnomer. B/c I was using incorrectly using {{ ansible_eth1.address }} instead of {{ ansible_eth1.ipv4.address }} elsewhere in the same task.

To sum this up, so this post is more useful for others. If you are trying to mark a host (i.e give it a host variable) so that it’s the only one that runs a task, here is what you do…

Inventory file:

[elasticsearch]
elasticsearch1 elasticsearch_purge_old_indices_node=yes
elasticsearch2

elasticsearch3

Task:

  • name: add a nightly cronjob task to purge node
    lineinfile: dest=/etc/crontab line=“0 1 * * * * root /path/to/script.sh” state=present
    when: elasticsearch_purge_old_indices_node is defined

The line “when: elasticsearch_purge_old_indices_node is defined” does two things.

  1. ensures only the host with elasticsearch_purge_old_indices_node defined runs that task.
  2. ensures you don’t get an error like “error while evaluating conditional”, because you haven’t defined elasticsearch_purge_old_indices_node for your other hosts.

Good day gentlemen!

-Mike