Test Driven Development of Dockerfile

This is sample project for Test Driven Development (TDD) of Dockerfile by RSpec. This means developing dockerfile by below cycle,

• Write Rspec test
• Build Docker image and run test -> RED
• Edit Dockerfile
• Build Docker image and run test -> GREEN
• Write Rs...

When developing Dockerfile, docker image, we should test pakage installation and dockerfile specific command like CMD or EXPOSE. To do this I use belows,

• To test package installation, serverspec
• To test docker specific command, docker-api which is Docker Remote API wrapper.

Environment

• OSX
• Docker on Vagrant VM

Usage

$ ./build_and_test.sh

This script executes belows,

1. Build image, docker -H :5422 build -t tcnksm/sample /vagrant/.
2. Run container, docker -H :5422 run -p 7654:22 -d serverspec /usr/sbin/sshd -D
3. Run rspec test, bundle exec rspec
4. Delete container, docker stop and docker rm

Vagrant

In advance, run Vagrant VM

$ vagrant up

Assgin private network IP to Vagrant VM. And out ssh configuration,

$ vagrant ssh-config --host docker-vm >> ~/.ssh/config

serverspec

Settings (ssh, sudoer)

To use serverspec, we need to prepare docker image which is prepared ssh and sudo user, see Dockerfile. In Dockerfile, to login the docker container by ssh without password, use public key on your localhost, prepare id_rsa.pub in project directory.

serverspec

To install,

$ gem install serverspec

Initialize,

$ bundle serverspec-init
Select OS type:

  1) UN*X
  2) Windows

Select number: 1

Select a backend type:

  1) SSH
  2) Exec (local)

Select number: 1

Vagrant instance y/n: n
Input target host name: 192.168.50.4

In Vagrantfile, private network IP "192.168.50.4" is assined to Vagrant VM. You should use it for target host name.

Edit ~/.ssh/config, using vagrant private network IP.

Host 192.168.50.4
  HostName 192.168.50.4
  User taichi
  Port 7654
  UserKnownHostsFile /dev/null
  StrictHostKeyChecking no
  PasswordAuthentication no
  IdentityFile /Users/taichi/.ssh/id_rsa
  IdentitiesOnly yes
  LogLevel FATAL

Set environmental variable for sudo,

export SUDO_PASSWORD="pass"

or

export ASK_SUDO_PASSWORD=1

Writing Rspec test

See sample spec/192.168.50.4/dockerfile_git_spec.rb. For more details, see documents

Docker Remote API

Settings

By default, docker deamon listen on unix:///var/run/docker.sock. (see here), To use it from external host, you should bind specific IP and port. To do this edit /etc/init/docker.conf. See docker.conf

Docker Remote API

Install,

$ gem install docker-api

Add below to spec_helper.rb

require "docker"
Docker.url = "http://192.168.50.4:5422"

IP is private IP assined Vagrant VM, port is bind port of docker deamon set by docker.conf

Writing Rspec test

See sample spec/192.168.50.4/dockerfile_spec.rb. For more details, see this blog post.

Reference

• serverspec - home
• Experimenting with test driven development for docker