How to extend a Dockerfile? - docker

Question

I have a Dockerfile that is similar to all of my builds. It only differs in the EXPOSE <Port>.
Question: how could I create some kind of a template-dockerfile that I could simply reuse across all of my projects?
I must put the template dockerfile in another (gitlab) repository, some kind of "docker-commons".
For example (the exact details of the dockerfile are not important for my question);
Dockerfile:
# syntax=docker/dockerfile:1
FROM maven:3.8.4-eclipse-temurin-11 as build
COPY pom.xml .
COPY src src
RUN mvn package
RUN java -Djarmode=layertools -jar target/*.jar extract
FROM debian:buster-slim
COPY --from=build /extract/dependencies/ ./
COPY --from=build /extract/spring-boot-loader/ ./
COPY --from=build /extract/snapshot-dependencies/ ./
COPY --from=build /extract/application/ ./
EXPOSE 8090
ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]
From a programmers point of view, I want to create a "static base template" that I can pass the "port" parameter. Something like:
Dockerfile:
extends base_dockerfile
EXPOSE 8090
ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]
Finally, I would then want to use that Dockerfile in different docker-compose.yml.

Answer 1

If the only params that change is the port you want to expose, you can override it whe you run the container. You don't need to expose a port in the Dockerfile, just bind it when you run the container.
https://docs.docker.com/engine/reference/builder/#expose
Using -p flag
docker run -p 80:80/tcp -p 80:80/udp ...
Or using ports in docker-compose (https://docs.docker.com/compose/networking/#configure-the-default-network)
version: "3.9"
services:
web:
build: .
ports:
- "8000:8090"
db:
image: postgres
networks:
default:
# Use a custom driver
driver: custom-driver-1
Edit:
if you already have an image on a registry you can simply reference it
version: "3.9"
services:
web:
image:gitlab.simultech.it:4567/<project_path>
ports:
- "8000:8090"
db:
image: postgres
networks:
default:
# Use a custom driver
driver: custom-driver-1
docker run -p 80:80/tcp -p 80:80/udp gitlab.simultech.it:4567/<project_path>