Automating python deployment environments setup with ansible

Prerequsites

to follow along with this post you would need the folowing installed on your machine

• ansible
• python3 (on your local machine and remote server).

In this post i will show you how you can automate creating python deployment environment's using Ansible.

But setting this up manually isn't a problem ?

say you have a web application that uses the flask framework, deploying this to an individual server manually wouldn't be a problem, scale this up to more than three applications with only slight variations in dependencies and things start to get pretty repetitive.This is where ansible comes in.

What's this ansible thing anyway ?

Ansible is an open source automation tool that can be used for configuration management, application deployment and infrastructure provisioning,to mention a few.

Ok lets do it then!

Start by creating the following folder structure.

Directory_Name
├── ansible.cfg
├── inventory
├── requirements.txt
└── playbook.yml

Lets start with ansible.cfg this is where we would set configuration values that we want ansible to use when it runs.

ansible.cfg

[defaults]
inventory = ./inventory

The above simply tells ansible to use the inventory file in the current directory.

Whats an inventory file?

ansible uses this to determine what what machine you would like to run your playbooks against.

inventory

[deployment server]
127.0.0.1

within the square brackets i specified the the name i would use to refer to a group of servers here i have just one but in practice 127.0.0.1 would be the ip address of the machines you want to run the playbooks.If you need to create a new group simply add another pair of square brackets and add the ip address of the targets machines below like above.If you would like to run this against your machine replace 127.0.0.1 with 127.0.0.1 ansible_connection=local,which is what i did.

Playbooks

playbooks in ansible simply refer to where you define the tasks you want to execute on the remote machine, playbooks are written in Yaml which is a markup language.

playbook.yml

---
- hosts: all
  gather_facts: true
  tasks:
    - name: install dependencies from requirements.txt
      pip:
        requirements: requirements.txt
        chdir: .
        executable: pip3


    - name: additional dependency
        pip:
          name: gunicorn
          executable: pip3

we use hosts to indicate what group we want to run the playbook against here i used all to run against all the ip addresses i have in my inventory, to run against a single group replace all with the name you placed within square brackets in the inventory ,ansible uses gather_facts to collect information about the target.

tasks is where we define what we actually want to do each task has a name which is used to make playbooks more readable and is also used in the output to indicate what task ansible is currently executing.pip3 is the ansible module we are using , when installing from a requirements.txt is i used chdir to tell ansible what path on my local machine the requirements.txt is located , in the second instance i pass the name of package i wish to install. you might want to install dependencies from a requirements.txt if you have specific version of your dependencies check out the ansible pip docs for more info.Now use ansible-playbook playbook.yml. Your output should look something like this

ok: [127.0.0.1]

TASK [install dependencies requirements.txt] ***********************************
changed: [127.0.0.1]

TASK [additional dependency] ***************************************************
ok: [127.0.0.1]

PLAY RECAP *********************************************************************
127.0.0.1                  : ok=3    changed=1    unreachable=0    failed=0    skipped=0    rescued=0    ignored=0   

PLAY RECAP is a summary of the tasks that where executed, ok tells you the number of tasks that ran successfully , changed shows you how many tasks changed the state of the target machine in this case 1 because i have some of the dependencies installed. The rest are pretty self explanatory so i would not dive into them.

If you would like to take a look at the source files for this post you can find them in this repository

If you're wondering where to go from here check out this post, that goes into more detail with Ansible tips and tricks

In a future post i would show you how to deploy a simple web app using ansible, if you have any questions feel free to reach me on twitter or create an issue in the repo.