Event-Driven Ansible

Let’s have a look at a minimal example which demonstrates how Event-Driven Ansible works. We imagine a situation in which we have a webserver running and want to monitor it. We can do that with the following rulebook:

# check_url_rulebook.yml
---
- name: Check webserver
 hosts: all
 sources:
 - ansible.eda.url_check:
 urls:
 - https://
 delay: 10
 rules:
 - name: Restart Nginx
 condition: event.url_check.status == "down"
 action:
 run_playbook:
 name: atix.eda.restart_nginx

This rulebook uses the url_check plugin to query the webpage at https://< webserver_fqdn > . every 10 seconds. There is only one rule. When the URL check returns a status of down, an Ansible playbook is automatically started. In this case, the Playbook started is installed under a private collection, atix.eda, and simply tries to restart the nginx service:

# restart_nginx.yml
---
- hosts: all
  gather_facts: false
  tasks:
    - name: Restart Nginx
      ansible.builtin.service:
        name: nginx
        state: restarted
      become: true

We can start monitoring the webserver with this command:

ansible-rulebook --rulebook check_url_rulebook.yml -i inventory.yml --verbose

Note that we must also pass an inventory file, inventory.yml, containing the hosts to be addresssed by the atix.eda.restart_nginx playbook. In this case, the inventory contains only one host, the webserver.

The above command runs in the foreground and listens for events.

When it hasn’t received an event yet, the output looks like this:

2023-11-29 13:53:07,183 - ansible_rulebook.rule_set_runner - INFO - Waiting for actions on events from Check url
2023-11-29 13:53:07 183 [drools-async-evaluator-thread] INFO org.drools.ansible.rulebook.integration.api.io.RuleExecutorChannel - Async channel connected
2023-11-29 13:53:07,184 - ansible_rulebook.rule_set_runner - INFO - Waiting for events, ruleset: Check url

Now, if we stop the webserver by hand, we will see first that the event is registered:

2023-11-29 13:54:37 407 [main] INFO org.drools.ansible.rulebook.integration.api.rulesengine.RegisterOnlyAgendaFilter - Activation of effective rule "Restart Nginx" with facts: {m={url_check={url=https://, status=down, error_msg=Cannot connect to host ssl:default [Connect call failed ('', 443)]}, meta={source={name=ansible.eda.url_check, type=ansible.eda.url_check}, received_at=2023-11-29T13:54:37.366718Z, uuid=709d45b8-803a-48e2-ad17-99d993c6e957}}}
2023-11-29 13:54:37,419 - ansible_rulebook.rule_generator - INFO - calling Restart Nginx

and then that the corresponding playbook is started:

2023-11-29 13:54:37,423 - ansible_rulebook.action.run_playbook - INFO - ruleset: Check url, rule: Restart Nginx
2023-11-29 13:54:38,425 - ansible_rulebook.action.run_playbook - INFO - Calling Ansible runner

PLAY [all] *********************************************************************

TASK [Restart Nginx] ***********************************************************
changed: []

PLAY RECAP *********************************************************************
         : ok=1    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   
2023-11-29 13:54:44,628 - ansible_rulebook.action.runner - INFO - Ansible runner Queue task cancelled