Conditional control structure in Jinja2 templates

Ansible uses Jinja2 as a template engine. Hence, it would be useful for us to understand Jinja2 control structures in addition to the ones supported by Ansible tasks. Jinja2's syntax encloses the control structures inside the {% %} blocks. For conditional control, Jinja2 uses the familiar if statements, which have the following syntax:

{% if condition %}
    do_some_thing
{% elif condition2 %}
    do_another_thing
{% else %}
    do_something_else
{% endif %}

Updating the MySQL template

The template that we created earlier to generate the my.cnf file assumes that all the variables referred in it are defined somewhere. There is a chance that this is not always the case, which could result in errors while running Ansible. Could we selectively include configuration parameters in the my.cnf file? The answer is yes. We could check whether a variable is defined and only then, we will add it to the file, as follows:

#filename: roles/mysql/template...