Testing Docker apps with Wercker

Wercker is a free and hosted continuous delivery platform with a lot of flexibility. Wercker offers everything you would expect from a modern CI service, and they recently announced full support for the Docker container runtime.

The Wercker platform has two modes (known as stacks) to run applications; Classic using custom made pre-built containers, and Ewok using the Docker container runtime. If you don’t know what Docker is, I suggest you read this article in order to get a basic understanding of Docker.

With the Ewok stack your application is run using Docker containers from Docker Hub - linked together just as you would have locally or in production. Yay for identical environments!!

Boxes

You application code is run in a primary container (known as a box). In Ewok the name this box is the name of a Docker image from Docker Hub + an optional image tag.

box: node:0.10

Services

Adhering to the Docker best practices you should only run a single process per container. If your application depends on another service (such as a database or a cache) you can link multiple containers together using services.

The services directive looks just like a box, but you can define as many of them as you like. They will automatically be linked together with your box before your application starts.

services:
    - mongo:2.6
    - redis:2.8

When Wercker starts, any service you have defined will be started and linked together with your box automatically. The IP-address of a given service will be available as a hostname corresponding to the name of the image. Any ports exposed by the container can be used as they are.

Wercker also has support for advanced service configurations, such as injecting custom environment variables and altering the startup command.

services:
    - id: mariadb
      env:
          MYSQL_ROOT_USERNAME: myusername
          MYSQL_ROOT_PASSWORD: mysecretpassword

Build Steps

Your containers are started and linked together, and it is time to run the build. This is done with one, or many, build steps. Wercker has an astonishingly amount of pre-defined build steps for every language in their step registry.

build:
    steps:
        - npm-install
        - npm-test

You can also submit your own build steps to the step registry, or script them in your build configuration using the script build step like this.

build:
    steps:
        - script:
            name: my custom script
            code: |
                # some command
                # more command

Putting it all togheter

And there you have it; box, services and build steps all go into one file in your project repository named wercker.yml. This is your Wercker build configuration file.

box: node:0.10

services:
    - mongo:2.6
    - redis:2.8

build:
    steps:
        - npm-install
        - npm-test

Getting Started

You can read more about the Wercker platform at devcenter.wercker.com, or check out their GitHub repo werkcer/docs where you can search through all of their documentation which is nicely formatted in Markdown.

Wercker also provides a lot of example projects to get you started. Check them out as well:

• Python Wercker Example
• Go Wercker Example
• Node.JS Wercker Example
• Ruby Wercker Example