docker expose, docker-compose expose

 

1. Dockerfile → EXPOSE

• Purely documentation/metadata.

• Doesn’t actually open or bind anything.

• Other containers on the same network can still reach your app via container_name:port even if you don’t EXPOSE it.

• Example: you can still curl http://web:8080 inside another container, even if the Dockerfile doesn’t have EXPOSE 8080.

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2. docker-compose.yml → expose:

• Same as Dockerfile’s EXPOSE, but defined in Compose instead.

• Makes the port visible to other containers in the same Compose network.

• Does not publish it to your host machine.

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3. docker-compose.yml → ports:

• This is the one that really matters if you want to access the container from outside Docker (e.g., browser, Postman, curl from host).

• Maps container port → host port.
  Example:

  ports:
    - "8080:80"   # host:container