08-systemd.rst

Day 8: service, systemd

Yesterday you were given the assignment of creating a collectstatic handler and a migrate handler. Here is the result to which you should have arrived:

- name: Collect static files for {{ django_project }}
  environment:
    PYTHONPATH: /etc/opt/{{ django_project }}
    DJANGO_SETTINGS_MODULE: settings
  command: >
    /opt/{{ django_project }}/venv/bin/python
    manage.py collectstatic --noinput
  args:
    chdir: /opt/{{ django_project }}

- name: Migrate {{ django_project }}
  environment:
    PYTHONPATH: /etc/opt/{{ django_project }}
    DJANGO_SETTINGS_MODULE: settings
  become: "{{ django_user }}"
  command: >
    /opt/{{ django_project }}/venv/bin/python
    manage.py migrate
  args:
    chdir: /opt/{{ django_project }}

The service module

Your next assignment is to configure nginx. For this you will create two tasks (nginx configuration file, nginx symbolic link) and one handler (reload nginx).

1. Create the nginx configuration file

Use the template Ansible module to create file /etc/nginx/sites-available/DOMAIN. The template file is this:

server {
   listen 80;
   listen [::]:80;
   server_name {{ django_domain }};
   root /var/www/{{ django_domain }};
   location / {
       proxy_pass http://localhost:{{ django_port }};
       proxy_set_header Host $http_host;
   }
   location /static/ {
       alias /var/cache/{{ django_project }}/static/;
   }
   location /media/ {
       alias /var/opt/{{ django_project }}/media/;
   }
}

Add the django_port parameter to the playbook.

2. Create the symbolic link

Use the file module to do the equivalent of these commands:

cd /etc/nginx/sites-enabled
ln -s ../sites-available/$DOMAIN

3. Reload nginx

Create a handler that uses the service module to perform the equivalent of this command:

service nginx reload

Make sure both tasks notify the handler.

Run the playbook and verify you did everything right.

The systemd module

Your final assignment is to install and configure Gunicorn. This will be three tasks and one handler.

1. Create a system service

Use the template module to create file /etc/systemd/system/DJANGO_PROJECT.service. These are the contents of the template:

[Unit]
Description={{ django_project }}

[Service]
User={{ django_user }}
Group={{ django_user }}
WorkingDirectory=/opt/{{ django_project }}
Environment="PYTHONPATH=/etc/opt/{{ django_project }}"
Environment="DJANGO_SETTINGS_MODULE=settings"
ExecStart=/opt/{{ django_project }}/venv/bin/gunicorn \
  --workers={{ gunicorn_workers }} \
  --bind=127.0.0.1:{{ django_port }} \
  --log-file=/var/log/{{ django_project }}/gunicorn.log \
  {{ django_project }}.wsgi:application

[Install]
WantedBy=multi-user.target

2. Install Gunicorn

Use the pip module to install Gunicorn in the virtualenv.

3. Enable and start the service

Use the systemd module to do the equivalent of these commands:

systemctl enable $DJANGO_PROJECT
service $DJANGO_PROJECT start

4. Restart the service

Create a handler that uses the service module to do the equivalent of this command:

service $DJANGO_PROJECT restart

Make sure the first two of the above tasks notify it, so that the service is restarted whenever gunicorn is upgraded or the service file changes. Also consider which other modifications should result in a restarting of the service, and make the related tasks also notify the handler.

When you finish, check if it's running. Visit the site on your browser and see if it works. If you are getting a server error, the most likely case is that you did not run collectstatic or migrate. Maybe you forgot to add the handlers to the notify option of the git install task or the settings.py task.

Congratulations! You finished deployment using Ansible. The only thing that needs to be fixed is that you might want to hide the secret key from people who have access to your Ansible repository. So tomorrow we will learn about the Ansible vault.