Provisioning django application using ansible

As I recently have opportunity of having a workshop about ansible in my work and I decided to write a blog post on how to provision django application using this tool.

What is ansible and how's is different from puppet

Ansible is a tool that helps automate boring tasks. These tasks are connected with setting up Linux machines, installing proper software on them and moving code from repositories to machines. Ansible has a different way of accomplishing these tasks than puppet. It is using push system - in short ansible connects to your machine via ssh and push changes. No need for masters and agents etc. Puppet, on the other hand, is using pull system which allows every machine to pull changes from master. Ansible is using the same principles as puppet so you declare how should host look like after running ansible.

Provisioning django application using ansible

I will be provisioning geodjango-leaflet. I assume that you know basic concepts of ansible like play, playbook or role. This is how a structure of my ansible repo looks like:

.
├── ansible.cfg
├── inventory
│ └── vagrant
│ └── hosts.ini
├── playbooks
│ ├── roles -> ../roles/
│ └── vagrant.yaml
├── roles
│ ├── db
│ │ └── tasks
│ │ └── main.yml
│ ├── geodjango
│ │ ├── handlers
│ │ │ └── main.yml
│ │ ├── tasks
│ │ │ └── main.yml
│ │ └── templates
│ │ ├── nginx.conf.j2
│ │ └── supervisord.conf.j2
│ ├── redis
│ │ └── tasks
│ │ └── main.yml
│ └── roles -> roles
└── Vagrantfile

Let's start from the bottom - Vagrantfile. I will be using vagrant as a playground. Configuration file a.k.a vagrantfile looks as follows:

VAGRANTFILE_API_VERSION = "2"

Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
config.vm.box = "trusty64"
config.vm.box_url = "https://cloud-images.ubuntu.com/vagrant/trusty/current/trusty-server-cloudimg-amd64-vagrant-disk1.box"
config.ssh.insert_key = false

config.vm.hostname = "vagrant-ansible"
config.vm.network "private_network", ip: "192.168.33.10"

config.vm.provision "ansible" do |ansible|
ansible.playbook = "playbooks/vagrant.yaml"
ansible.inventory_path = "inventory/vagrant/hosts.ini"
ansible.sudo = true
ansible.verbose = "v"
ansible.limit = "all"
end

end

I setup basic private_network with ip of a vagrant box. In config.vm.provision I specified playbook which should be run in vagrant and inventory where the configuration of my hosts lay. This inventory presents itself below:

vagrant-ansible ansible_ssh_host=192.168.33.10 ansible_ssh_port=22

My ansible playbook don't have tasks inside it but I delegate it to roles:

---
- hosts: vagrant-ansible
become: yes

roles:
- db
- geodjango
- redis

Let's start with the first role: db. In folder with this role, I have tasks folder with main.yml:

---
- name: ensure apt cache is up to date
apt: update_cache=yes

- name: ensure packages are installed
apt:
name: ""
with_items:
- postgresql
- libpq-dev
- python-psycopg2
- postgresql-9.3-postgis-2.1
- python3-dev
- python-dev

- name: ensure database is created
become_user: postgres
postgresql_db:
name: geodjango

- name: ensure user has access to database
become_user: postgres
postgresql_user:
db: geodjango
name: geodjango
password: geodjango
priv: ALL

- name: enable postgis for database
become_user: postgres
postgresql_ext:
name: postgis
db: geodjango

In this task, I run apt-get update at the top then I install a couple of packages so I can setup Postgres. Right below that I create db, grant user access to that db and create PostGIS extension. As this role completes ansible will execute geodjango role:

---
- name: ensure packages are installed
apt:
name: ""
with_items:
- binutils
- libproj-dev
- gdal-bin
- git
- python-virtualenv
- build-essential
- postgresql-server-dev-all
- supervisor
- nginx

- name: ensure git repo is present
git:
repo: https://github.com/krzysztofzuraw/geodjango-leaflet.git
dest: /opt/geodjango

- name: create virtualenv
command: virtualenv /opt/venv -p python3.4 creates="/opt/venv"

- name: install requirements
pip:
requirements: /opt/geodjango/requirements.txt
executable: /opt/venv/bin/pip

- name: migrate django application
django_manage:
command: migrate
virtualenv: /opt/venv
app_path: /opt/geodjango

- name: load django initial data
django_manage:
command: load_inital_voivodeships
virtualenv: /opt/venv
app_path: /opt/geodjango

- name: collect static files
django_manage:
command: collectstatic
virtualenv: /opt/venv
app_path: /opt/geodjango

- name: ensure config dir for supervisor extists
file:
slug: /etc/supervisor/conf.d
state: directory

- name: ensure supervisor config is present
template:
src: templates/supervisord.conf.j2
dest: /etc/supervisor/conf.d/geodjango.conf
notify: reread supervisor

- name: remove default nginx configuration
file:
name: /etc/nginx/sites-enabled/default
state: absent

- name: ensure nginx config is present
template:
src: templates/nginx.conf.j2
dest: /etc/nginx/sites-enabled/geodjango.conf
notify: restart nginx

This code above is self-explanatory but I will write closely about task called create virtualenv. Normally you can write this and next one task in one like:

pip:
requirements: /opt/geodjango/requirements.txt
virtualenv: /opt/venv

And if this virtualenv is not present it will be created. But there is a bug in ansible that is causing these requirements to be installed in system wide python, not virtualenv one. Reference is here. I use fix provided by one of the guys in this issue discussion - I break this task into two separate: one for creating virtualenv and second one for installing requirements.

What is different in this task is that I'm also using templates for supervisor and Nginx. They have j2 ending as ansible is using jinja2 template system. During the ansible run, they will be copied to given dest. At the end of tasks with templates I have notify keyword which tells ansible to look for handlers folder with tasks for restarting services. In my case they look as follows:

---
- name: reread supervisor
supervisorctl:
name: geodjango_leaflet
state: present

- name: restart nginx
service:
name: nginx
state: restarted

The last role is redis. This code installs redis-server and starts it:

---
- name: ensure redis packages are installed
apt:
name: ""
with_items:
- redis-server

- name: ensure redis is started
become: true
service:
name: redis-server
state: started
enabled: yes

My thoughts and feelings about ansible

I have to say I'm really impressed on how simple is to write ansible tasks. With puppet, I have this problem that I need to look for modules in puppet forge or write my own. Here everything is included. You want to use django commands -use django_manage, need to reread supervisor config use present in supervisorctl task. Really simple and fun to work with. I can quickly get a job done and move to another stuff.

Yet, I don't know how ansible will behave when it comes to provisioning a large amount of machines. Here I have only one host and it's going smoothly, but for sure when I will have a need for provisioning my private machines I will choose ansible.

That's all for this week blog post! Feel free to comment - I really appreciate that.

Repo with this code is available on github.

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