How to specify different port for a Docker postgres instance?

Question

I am trying to get a postgres container running on a different port (5433 instead of the default 5432) per several online threads like this one: https://github.com/docker-library/postgres/issues/196#issuecomment-310209118

(The reason for the port change is because an unrelated project that I leave running is already using port 5432 so I'd like to be able to run rspec simultaneously on multiple projects.)

In my test ENV I have DATABASE_URL=postgresql://postgres:@db.local:5433/test_agile_self

Everything worked when I was using port 5432 (in DATABASE_URL and docker-compose.yml)

After changing the port to 5433, when I run rspec I get:

PG::ConnectionBad:
  could not connect to server: Connection refused
    Is the server running on host "db.local" (172.22.0.2) and accepting
    TCP/IP connections on port 5433?
# ./spec/spec_helper.rb:62:in `block (2 levels) in <top (required)>'

The container does indeed seem to be running on port 5433 and IP address 172.22.0.2:

$ docker ps
CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES
a8f5dee227e8        postgres:10.5       "docker-entrypoint.s…"   27 minutes ago      Up 14 seconds       0.0.0.0:5433->5432/tcp   zarc_db.local_1

$ docker inspect a8f5dee227e8 | grep "IPAddress"
            "SecondaryIPAddresses": null,
            "IPAddress": "",
                    "IPAddress": "172.22.0.2",

My docker-compose.yml uses the ports: "5433:5432" as per the discussion linked above.

#docker-compose.yml
version: '3'
services:
  web:
    build: .
    ports:
      - "3010:3010"
    volumes:
      - .:/my_app
    links:
      - db.local
    depends_on:
      - db.local

  db.local:
    image: postgres:10.5
    ports:
      - "5433:5432"

If I change 5433 back to 5432 in those two spots (ENV and docker-compose.yml) it works again.

This is on a Mac running Mohave 10.14.3, and Docker 18.09.2

Answer 1

Inside the container, so in DATABASE_URL the port needs to stay the same 5432, i.e. it has to match the DB config inside the container. In the docker-compose you only map the existing port 5432 to the outside world as 5433 using the given

ports:
    - "5433:5432"

Answer 2

In your docker-compose you can add this: (Long-Syntax)

ports:  
  - target: 80
    published: 8080
    protocol: tcp
    mode: host

Where,

• target: the port inside the container
• published: the publicly exposed port
• protocol: the port protocol (tcp or udp)
• mode: host for publishing a host port on each node, or ingress for a swarm mode port to be load balanced.

Alternatively a one-liner: (Short-Syntax)

ports:
  - "4040:5432" # HOST:CONTAINER

Where,

• 4040 is port to be exposed on the HOST
• 5432 is port exposed on container

NOTE:

You may experience erroneous results when using a container port lower than 60, because YAML parses numbers in the format xx:yy as a base-60 value. For this reason, we recommend always explicitly specifying your port mappings as strings.