D4: Dock to Develop Dynamic Dockerfile

abstract

D4 is the tool to develop generic Dockerfile. D4 will provide the easier method to build container image from Dockerfile and test the Dockerfile. By this method, you can realize TDD(Test Driven Development) of Dockerfile easily.

requirements

D4 requires the following software.

• docker
• container-structure-test
• python 3.4+
• python packages
  • docker
  • pyyaml

install

$ pip install d4

quick start

1. Create project httpd

   $ d4 init httpd
   $ cd httpd
   

2. Describe image name and registry server in common.yaml

   image_name: <your dockerhub username>/httpd:latest
   registry_server: docker.io
   

3. Describe test code in tests/config.yaml

   schemaVersion: '2.0.0'
   commandTests:
   - name: "check httpd pkg"
     command: "rpm"
     args:
     - "-qa"
     expectedOutput:
     - "httpd-.*"
   metadataTest:
     exposedPorts:
     - "80"
     cmd:
     - "httpd"
     - "-DFOREGROUND"
   

4. Describe mock in Dockerfile

   FROM docker.io/centos:latest
   

5. Run develop subcommand and confirm test fails

   $ d4 develop
   

6. Describe implementation in Dockerfile

   FROM docker.io/centos:latest
   RUN yum install -y httpd
   EXPOSE 80
   CMD ["httpd", "-DFOREGROUND"]
   

7. Run develop subcommand and confirm test succeeds

   $ d4 develop
   

8. Release image to your repository of dockerhub

   $ d4 release -u <your dockerhub username> -p <your dockerhub password>
   

usage

project directory architecture

d4 project need to have the following directory architecture;

(project name)
|-- Dockerfile
|-- build.yaml
|-- common.yaml
`-- tests
    |-- config_1.yaml
    |-- ...
    `-- config_N.yaml

• Dockerfile
  The Dockerfile which belongs to the project. For this Dockerfile, container image will be built and test will be executed.

• build.yaml
  The yaml file which has arguments to be used by building image. All arguments of the Dockerfile should be described in this file. for example;

  args:
    ARG_1: "VALUE_1"
    ARG_2: "VALUE_2"
    ARG_3: "VALUE_3"
  

• common.yaml
  The yaml file which has parameters to be used by both building image and testing image. for example;

  image_name: bbrfkr0129/httpd:latest
  registry_server: docker.io
  

• tests/<yaml config file>
  The yaml files which has tests to be used by testing image. These tests in the yaml files need to be written as container-structure-test can be processed.

TDD method with D4

1. Create project with subcommand init. By this subcommand, basis directory architecture and sample files are created.

   $ d4 init tdd_project
   $ cd tdd_project
   $ tree . --charset=C
   .
   |-- Dockerfile
   |-- build.yaml
   |-- common.yaml
   `-- tests
       `-- config.yaml
   

2. Specify developed image name and registry server pushed developed image in common.yaml;

   $ cat <<EOF > common.yaml
   image_name: <your dockerhub username>/tdd_image:latest
   registry_server: docker.io
   EOF
   

3. Write mock in Dockerfile and build.yaml. Implementation is not done yet.

   $ cat <<EOF > Dockerfile
   FROM <base image name>:<tag>
   EOF
   $ cat <<EOF > build.yaml
   args:
   EOF
   

4. Write test code according to the syntax of container-structure-test in tests/config.yaml. In TDD, test code is written before writing Dockerfile.

5. Execute test with subcommand develop. By this subcommand, mock container image is built and tested. Then tests should be failed.

   $ d4 develop
   

6. Write implementation of Dockerfile and build.yaml. In build.yaml, The arguments in ARG statements of Dockerfileshould be written;

   args:
     ARG_1: "VALUE_1"
     ARG_2: "VALUE_2"
     ARG_3: "VALUE_3"
   

7. Execute build and test with subcommand develop. By this subcommand, implementation of Dockerfile is applied, and then generated container image is tested. All tests should be passed.

   $ d4 develop
   

8. Repeat procedures 4.-7.. until required container image is got.

9. Release got container image to registry server with subcommand release. By this subcommand, final build and test will be processed, then pushed to registry server specified in common.yaml.

   $ d4 release
   

10. Run container from pushed container image!

    $ docker run <your dockerhub username>/tdd_image:latest
    

valid subcommands

• d4 init
  Create and initialize project.

• d4 build
  Only build process runs.

• d4 test
  Only test process runs.

• d4 login
  Only login into registry server specified in common.yaml.

• d4 push
  Only push container image specified in common.yaml.

• d4 develop
  build and test processes run.

• d4 release
  build, test, login and push processes run.