using shared dockerfile for multiple dockerfiles

Question

What I have, are multi similar and simple dockerfiles

But what I want is to have a single base dockerfile and my dockerfiles pass their variables into it.

In my case the only difference between dockerfiles are simply their EXPOSE, so I think it's better to keep a base dockerfile and other dockerfiles only inject that variables into base dockerfile like a template engine

A sample dockerfile:

FROM golang:1.17 AS builder
WORKDIR /app
COPY . .
RUN go mod download
RUN go build -o /bin/app ./cmd/root.go

FROM alpine:latest
WORKDIR /bin/
COPY --from=builder /bin/app .
EXPOSE 8080
LABEL org.opencontainers.image.source="https://github.com/mohammadne/bookman-auth"
ENTRYPOINT ["/bin/app"]
CMD ["server", "--env=dev"]

Answer 1

IMPORT directive will never be implemented

A long time ago there was proposed IMPORT directive for Docker

Unfortunately, issues are closed while PR's are still open:

• docker - using shared dockerfile for multiple dockerfiles - Stack Overflow
• Proposal: Dockerfile add INCLUDE · Issue #735 · moby/moby
• implement an INCLUDE verb/instruction for docker build files · Issue #974 · moby/moby
• Add INCLUDE feature · Issue #40165 · moby/moby
• docker build: initial work on the include command by flavio · Pull Request #2108 · moby/moby
• Dockerfile templating to automate image creation
• Templating your Dockerfile like a boss! | by Ahmed ElGamil | Dockbit

Solution for your case

But for your case, all you need - is just a bit of sed

E.g.:

# Case1: inplace templating
EXPOSED_PORT=8081 sed -i "s/EXPOSE 8080/EXPOSE $EXPOSED_PORT/" Dockerfile

# Case2: generating Dockerfile from template
sed "s/EXPOSE 8080/EXPOSE $EXPOSED_PORT/" Dockerfile.template > Dockerfile

Explanation:

• EXPOSED_PORT=8081 declares local bash variable
• sed is a tool for text manipulation
• sed -i "s/EXPOSE 8080/EXPOSE $EXPOSED_PORT/" Dockerfile replaces EXPOSE 8080 to EXPOSE 8081
• sed "s/EXPOSE 8080/EXPOSE $EXPOSED_PORT/" Dockerfile.template > Dockerfile generates the new Dockerfile from Dockerfile.template