Templating for Dockerfiles.
It is common for Dockerfiles to share a similar base with slight modifications. It happens when applying the same changes from different base images, or tuning images for production / development.
For those cases it might be useful to have a simple template which can be used to generate different "flavours" of the same Dockerfile.
Prebuilt binaries are available in the releases.
go get github.com/bamarni/dockplate
# ./Dockerfile.template
FROM debian:{{.Env.BASE_TAG}}
# Common steps
# ...
{{if eq .Env.ENVIRONMENT "prod"}}
# Production tweaks
# ...
{{else if eq .Env.ENVIRONMENT "dev"}}
# Development tweaks
# ...
{{end}}
RUN ...
CMD ...
The template parser is based on golang's text/template,
cf. https://golang.org/pkg/text/template/ for full reference.
You can then generate Dockerfiles like this :
BASE_TAG=jessie ENVIRONMENT=prod dockplate < Dockerfile.template > jessie-prod/Dockerfile