Day 6: Loops, “file” module, “template” module¶

Yesterday, when we converted the greeter role to a reusable django role, we determined that the installing of python3-pillow is specific to greeter and does not belong in a general, reusable django role. There are two solutions to that.

Executing extra tasks¶

The first solution is very simple. Modify your playbook, site.yml, and make it like this:

---
- name: Install greeter server
  hosts: example.com
  tasks:
    - name: Install extra apt packages for greeter
      apt:
        name:
          - python3-pillow
  roles:
    - role: django
      django_project: greeter
      django_project_repository: https://github.com/djangodeployment/greeter.git
      django_user: greeter
      django_project_python: python3
      django_project_site_packages: yes

You should also remove the Pillow installation from roles/django/tasks/main.yml, if it’s still there.

Loops¶

This is the alternative solution, but we are not going to implement it right now:

I’m just showing it to you so that you get an idea of how we accomplish loops in Ansible. On the one hand this is better because the installation of the package goes inside the role definition, which is logically the correct thing to do. The problem of this solution is that it is less general. It solves only the problem of installing extra packages, but maybe some Django project could need something else besides package installation. You can choose any solution you like, or a combination. For the moment we will go with the previous solution.

The file module¶

Before continuing with the file module, let me show the directories we are using in this course while deploying Django:

It probably looks a bit strange to you. Most people aren’t doing this; instead they are putting all files under a single directory which is something like /home/django or /srv/django perhaps. I prefer to follow the Filesystem Hierarchy Standard. It’s very good for educational purposes and I also use it because it’s very clean, it’s convenient for backup and automation and it can scale.

Now it’s time for another assignment. Create three tasks that will create the data, log, and configuration directories. The tasks must do the equivalent of these commands:

mkdir /var/opt/$DJANGO_PROJECT
chown $DJANGO_USER /var/opt/$DJANGO_PROJECT
mkdir /var/log/$DJANGO_PROJECT
chown $DJANGO_USER /var/log/$DJANGO_PROJECT
mkdir /etc/opt/$DJANGO_PROJECT
chgrp $DJANGO_GROUP /etc/opt/$DJANGO_PROJECT
chmod 750 /etc/opt/$DJANGO_PROJECT

Hint:

Use the Ansible file module

You should spend 5–10 minutes on that. Scroll down to see the answer.

⇓

Here is the answer:

- name: Create data directory /var/opt/{{ django_project }}
  file:
     path: /var/opt/{{ django_project }}
     state: directory
     owner: "{{ django_user }}"

- name: Create log directory /var/log/{{ django_project }}
  file:
     path: /var/log/{{ django_project }}
     state: directory
     owner: "{{ django_user }}"

- name: Create config directory /etc/opt/{{ django_project }}
  file:
     path: /etc/opt/{{ django_project }}
     state: directory
     group: "{{ django_user }}"
     mode: 0750

One thing you must be careful about is that the 750 must be preceeded by a zero. The reason is that the YAML parser interprets this as a number and in YAML the number is octal if it begins with zero.

You may have noticed here that I’m using a variable that makes the task name unique. If you install two Django projects on the same machine you would use the same role twice, so if you didn’t use a variable you would have two tasks with the same name. This will usually not be a problem in tasks, but it is a problem with handlers. If a task decides to trigger a handler, and there are two handlers with the same name, Ansible will not know which handler is meant. So all handlers must have a variable in their name if the role might be assigned more than once on a given machine. I often do this in tasks as well, out of habit.

The template module¶

Here is another assignment for you. We are going to create settings.py.

Step 1¶

Copy this and put it in file roles/django/templates/settings.py.j2:

from {{ django_project }}.settings import *

DEBUG = False
ALLOWED_HOSTS = ['{{ django_domain }}']
SECRET_KEY = '{{ django_secret_key }}'
DATABASES = {
    'default': {
        'ENGINE': 'django.db.backends.sqlite3',
        'NAME': '/var/opt/{{ django_project }}/{{ django_project }}.db',
    }
}
STATIC_ROOT = '/var/cache/{{ django_project }}/static/'
STATIC_URL = '/static/'
MEDIA_ROOT = '/var/opt/{{ django_project }}/media/'
MEDIA_URL = '/media/'

Step 2¶

Write another task (in roles/django/tasks/main.yml) that will create /etc/opt/greeter/settings.py, using the Ansible templates module.

Step 3¶

Expand the compile handler to also compile the configuration directory, and have the new task notify it.

Step 4¶

Add the django_domain and django_secret_key parameters to the playbook.

Step 5¶

I trust you can do this assignment on your own and I will not give you the result. Tomorrow we will create two more handlers.