Ansible Post Tasks Execution Condition

ansible

I'd like to know, in which condition an Ansible post_task will be executed? If the pre-tasks or roles had any failure, would the post-tasks be executed?

For example, I'd like to clean up the server if and only if it is stopped. In the following script, will the server_dir be removed if server is not stopped correctly?

---

- hosts: webservers

  pre_tasks:
    - shell: echo 'stopping server...'

  roles:
    - { role: stop_server }

  post_tasks:
    - file: path="{{ server_dir }}" state=absent

Best Answer

Tasks under post_tasks will not be executed when the previous tasks failed (meaning that the return code of the task isn't 0). That is the default behavior of Ansible and part of the design of Ansible:

Ansible is actually designed to be a “fail-fast” and ordered system [...]

Ansible test_strategies

fail-fast means Ansible will stop the execution of the whole play as soon as one task fails (as long as you don't set ignore_errors: True parameter for the task.)

The documentation on post_tasks is incomplete but if you write yourself a small test playbook and role you will see that Ansible behaves as expected.

Which makes sense because you might want to use pre_tasks and post_tasks to remove and add a node from and to a cluster and you don't want your node to be added to a cluster when the role didn't executed without errors.

Related Solutions

Callbacks or hooks, and reusable series of tasks, in Ansible roles

I'm not familiar with PostgreSQL so I'm unsure of the contents of the various configuration files you mentioned, but if you need to allow multiple roles to contribute to a single configuration file, I've accomplished this in one of two ways depending on what the configuration file supports:

Use a configuration file with lots of include statements to include additional configuration files located in sub-directories. This works well with something like Apache for rewrite rules, application-specific configuration directives, and virtual hosts.
Assemble the configuration file from multiple partial configuration files stored in a directory using the assemble module. I've used this method to construct a master.cf file for Postfix as I had a postfix role and another role that needed to add to the Postfix master.cf file. So I modified the postfix role to create a /etc/postfix/master.d directory and a handler that assembles the files in that directory into a master.cf file. Unfortunately, as you pointed out, since I can't call the handler in the postfix role from another role, I had to duplicate that handler in my additional role. It's slightly less than idea but it works and it's idempotent.

Ansible – Appending to Lists or Adding Keys to Dictionaries

You can merge two lists in a variable with +. Say you have a group_vars file with this content:

---
# group_vars/all
pgsql_extensions:
  - ext1
  - ext2
  - ext3

And it's used in a template pgsql.conf.j2 like:

# {{ ansible_managed }}
pgsql_extensions={% for item in pgsql_extensions %}{{ item }}, {% endfor %}

You can then append extensions to the testing database servers like this:

---
# group_vars/testing_db
append_exts:
  - ext4
  - ext5
pgsql_extensions: "{{ pgsql_extensions + append_exts }}"

When the role is run in any of the testing servers, the aditional extensions will be added.

I'm not sure this works for dictionaries as well, and also be careful with spaces and leaving a dangling comma at the end of the line.

Best Answer

Related Solutions

Callbacks or hooks, and reusable series of tasks, in Ansible roles

Ansible – Appending to Lists or Adding Keys to Dictionaries

Related Topic