This tool is provided to supersed Dockerfile, with easier to write command, less intermediate images and smart content detection.

Given a yaml template file, it create a script, and generate a docker file that will execute it.

The template is made of parts, each one generating a specific kind of action: installing packages, extracting tar, installing files, or custom script.

The template can contain variable that will be resolved at execution time.

A template must contains the following items:

• tag, map to --tag= in docker build command
• from, map to FROM in the Dockerfile
• maintainer, map to MAINTAINER in the Dockerfile
• environment, map to ENV in the Dockerfile, it must be an mapping
• command, map to CMD in the Dockerfile
• entrypoint, map to ENTRYPOINT in the Dockerfile
• execute, a sequence of step to execute.

Step types

A step is made of a mapping that define it.

The most common key is type that define the kind of action that this step is.

There is 3 possible way to define the content of a step:

• the key content, it will be used as is.
• the key source, it's the path to a file, it will be copied
• the key url, the content will be downloaded

Content can be given with multi line, in the yaml way:

content: |
    line 1
    line 2

Initial space will be ignored

packages

A set of package to install

script

A shell script to execute, it will be executed with bash

script

A command to execute.

file

A file to install

Additionnal keys can be given:

• file_name, the final file name, inside the image
• mode, a octal set of permission
• owner, the final owner of the file, in the format user:group ; it can be symbolic or numeral, but it will be resolved within the image.

Variables

The template can use variable, they are defined in the format ${{variable_name}}.

They are given as -v name value in the command line

It the template contains a variables section, it can define new variable. In this case, each element is a new variable and a python expression that will resolve it, using the already defined variables.

For example, if dockercreate is launched with -v key 1 and the template containes:

variables:
   v1: int(key) * 2
   v2: {'1': 'a'}[key]

it will add a variable v1 with value 2 and v2 with value 'a'. All variable are strings and so must be converted before use a int or other types