0

I struggle a bit with Docker and ports, but here's my situation. I have a Docker compose file which spins up a Postgres DB and adminer, the admin GUI. Here's my (truncated) config:

  # database
  db:
    image: postgres:14.2
    volumes:
      - .psqlrc:/root/.psqlrc:ro
      - dbdat:/var/lib/postgresql/data
      - ./log:/root/log:cached
      - ./latest.dump:/latest.dump
    environment:
      POSTGRES_DB: hlp-api-dev
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      DB_PORT: 5432
    ports:
      - 5432
    healthcheck:
      test: pg_isready -U postgres -h 127.0.0.1
      interval: 5s

  # database admin
  dbAdmin:
    image: adminer
    ports:
      - 8080
    depends_on:
      - db

That all works fine - but HTTP access to adminer is seemingly random port chosen by Docker e.g.

http://localhost:57014

...which I can find out only by clicking the brower button next to its container within Docker Desktop. How can I dictate this port, and why isn't it accessible at

http://localhost:8080

...which is the port listed?

If I try to specify another port, i.e.

ports:
  - 8080
  - 5000 # my choice

...then it doesn't spin up on any port at all. Even if I click the browser button within DD, I get "connection reset" in the browser.

Mitya
  • 33,629
  • 9
  • 60
  • 107

1 Answers1

1

Yes you can. If you specify two port numbers as xxxx:yyyy, the first one will be the host port and the second will be the internal container port that the app is listening on. Adminer listens on 8080 so that on is fixed. But you can freely choose the host port. So to access it on http://localhost:5000/, you'd do

  # database admin
  dbAdmin:
    image: adminer
    ports:
      - 5000:8080
    depends_on:
      - db

You can do the same on the Postgres container if you want.

Hans Kilian
  • 18,948
  • 1
  • 26
  • 35
  • Thank you, that works. So was I wrong in thinking that `- 8080` is equivalent to `- 8080:8080`? And if I'm right, how come it wasn't accessible on localhost:8080? – Mitya Apr 23 '22 at 16:20
  • 1
    When you use the `- 8080` syntax, Docker maps a random port on the host to port 8080 in the container. You almost always want to specify the host port yourself and use the `- 5000:8080` syntax. – Hans Kilian Apr 23 '22 at 16:36
  • Got it! I was (wrongly) assuminng that specifying a single value doubled it as though I'd put the same value twice, colon-separated. – Mitya Apr 23 '22 at 16:58