docker-gen

docker-gen is a simple tool that generates Dockerfiles from a base template and provided values.

Build

To build, simply use the provided Makefile:

make build

This will put the binary in the bin directory.

Usage

Full usage information is available by running docker-gen --help.

docker-gen generates validated Dockerfiles from go templated Dockerfiles.

Usage:
  docker-gen [flags]
  docker-gen [command]

Available Commands:
  completion  Generate the autocompletion script for the specified shell
  help        Help about any command
  run         Renders Dockerfiles from templates with provided values
  version     Print the version of docker-gen

Flags:
  -h, --help   help for docker-gen

For the run command, the following options are available:

Usage:
  docker-gen run [flags]

Flags:
  -d, --data-file string      File containing data to use in template
  -f, --force                 Print rendered Dockerfiles even if they don't pass validation
  -h, --help                  help for run
  -o, --output-dir string     Directory to write rendered Dockerfiles to. Defaults to data directory if not piped to something else.
  -s, --stdout                Write rendered Dockerfiles to stdout
  -t, --template-dir string   Directory containing templates

Examples

To generate a simple Hello World Dockerfile from the base template using the provided values, run the following command:

bin/docker-gen run -d applications/hello/hello-values.yaml -t templates base

This will be default output the final Dockerfile next to the values, in this case applications/hello/Dockerfile. To output the Dockerfile to a different directory, use the -o flag.

stdin/stdout

You can also pipe the output to another command, for example to build the image:

bin/docker-gen run -d applications/hello/hello-values.yaml -t templates base | docker build -t hello -f - applications/hello

Here we get the Dockerfile from stdin (-f -). We set the context (the last input) to applications/hello since we use COPY commands in the Dockerfile, so we need the correct context.

We can also pipe in the values from stdin, pipe the output to stdout, and print the final Dockerfile to the my-dockerfiles/ output directory:

cat applications/hello/hello-values.yaml | bin/docker-gen run -t templates -o my-dockerfiles/ base | docker build -t hello -f - applications/hello

CI

To test the CI locally, install act and run the following command:

act -P ubuntu-latest=catthehacker/ubuntu:act-latest \
    -s GITHUB_TOKEN='my-github-token' \
    -s DOCKERHUB_TOKEN='my-secret-token'

The Dockerhub token is only required if you want to push the image to Dockerhub, you could simply comment out the Login to DockerHub step when testing locally. The Github token is required in the Docker Tags step as it uses the Github API to get the latest metadata it seems. Can't really get around it in a nice way.

TODO

• Add built-in Dockerfile validation.

• Add support for stdin/stdout.

• Convert to Github Action. If this was to be used by multiple projects, writing a Typescript Github Action would be the way to go.

• Make it a library + cmd CLI. Having it all in the cmd dir isn't very neat or flexible.

• Add more flexible options in the template renderer. Right now the values are hardcoded, so we'd need to make it more flexible.

• CI tidy up. A lot of hardcoded values.