dockalot 0.5.0

Build Docker images for the real world using ansible playbooks

Building Docker images for the real world.

dockalot is a tool to help building Docker images using Ansible playbooks as the provisioning language. It addresses several shortcomings with the default Docker toolkit to make building non-trivial images much more practical.

Using a Dockerfile is fine if you are repackaging an open source or other publicly available package. But if you aren’t, you might have one or more of these problems:

• Building your image requires credentials to a private source code or package repository

• Building your image requires a custom package installation procedure more complicated than apt-get install

Because of the way docker build works by building your image in layers on top of layers, you may find that your super-secret private repository credentials gets trapped in one of those layers. Go ahead, export an image using docker save and poke around the layers of an image you’ve already built. Is that your access token in there? Well, it’s everyone’s access token now…

Temporary files part of any non-trivial package installation also get trapped in those middle layers causing your final Docker image to be much larger than they need to be. Workarounds for this problem include &&-itis; joining dozens of shell commands together with && in an attempt to keep them all on the same layer. When you do this you lose the ability to add comments in-line and your Dockerfile becomes a mess.

It doesn’t have to be this way.

dockalot solves these problems by executing all of the provisioning in one Docker layer. There are no hidden layers for credentials or temporary files to hide in. You can focus on just installing software into your Docker image and let the tools handle the rest.

Example Use

Requirements:

• Docker >= 1.12

Try it out with one of the examples that comes with the source code:

dockalot examples/mysql/mysql-5.7.yml

Configuration File

The configuration file for dockalot is a single YAML file containing 2 sections separated by ---. The first section contains the configuration for the Docker image to build. The second section is a full-blown Ansible playbook that you can make as simple or as complex as you need.

A simple configuration file:

---
docker:
  base_image: "python:2.7-slim"
  entrypoint: [ "/entrypoint.py" ]
---
- name: Provision the container
  hosts: all
  tasks:
    - name: Install the thing
      copy:
        dest: /entrypoint.py
        content: |
          #!/usr/bin/env python
          print("I'm a Python script")
          print("Wheeeeee!!!!")
        mode: 0755

Also check out the examples directory for more examples!