Postgres in Docker port matching - postgresql

Question

I need to run several equals Postgres containers on different ports via docker-compose. My problem is that I do not understand how to connect from my terminal to container's psql.
First of all, I should say that my local Postgres is off, so 5432 is free. Also I have listen_addresses = '*' in my containers.
Here is list of my attempts (to make it easier, I've posted examples for one Postgres container):
Run without port specifying
docker-compose.yml:
version: "3"
services:
postgres:
build:
context: ../../
dockerfile: db-load-test/sharding-benchmark/Dockerfile
environment:
- POSTGRES_PASSWORD=postgres
check port:
$ docker-compose ps
Name Command State Ports
--------------------------------------------------------------------------------
sharding-benchmark_postgres_1 docker-entrypoint.sh postgres Up 5432/tcp
try to connect:
$ psql -p 5432 -U postgres
psql: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
$ psql -h localhost -p 5432 -U postgres
psql: could not connect to server: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?
$ psql -h 0.0.0.0 -p 5432 -U postgres
psql: could not connect to server: Connection refused
Is the server running on host "0.0.0.0" and accepting
TCP/IP connections on port 5432?
Specify port and expose it in .yaml (I've changed 5432 to 5433 to make it more expressive)
$ docker-compose ps
Name Command State Ports
----------------------------------------------------------------------------------------------------------------------------
sharding-benchmark_postgres_1 docker-entrypoint.sh postgres Up 5432/tcp, 0.0.0.0:49162->5433/tcp,:::49162->5433/tcp
Similar attempts to connect was unsuccessful. Also it's unclear to my why Postgres still listen 5432:
postgres_1 | 2021-08-02 12:49:01.394 UTC [1] LOG: listening on IPv4 address "0.0.0.0", port 5432
postgres_1 | 2021-08-02 12:49:01.394 UTC [1] LOG: listening on IPv6 address "::", port 5432
postgres_1 | 2021-08-02 12:49:01.397 UTC [1] LOG: listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
Use docker directly
docker run --rm -it -e POSTGRES_PASSWORD=postgres -p 5432:5432/tcp postgres:11
It works with psql -h localhost -p 5432 -U postgres, but if I use docker run with 5432:5433 it breaks, which is unclear to me.

Answer 1

In your docker-compose.yml file, you need to specify ports: for each of the database containers. In each of these the second number must be the normal port for the database (5432); the first number can be any number of your choosing that's not used by another container or host process.
version: '3'
services:
pg1:
image: postgres
# Use default PostgreSQL port 5432 on the host
ports: ['5432:5432']
pg2:
image: postgres
# First port must be different from pg1's above
# Second port must be exactly 5432
ports: ['5433:5432']
When you connect from the host, use a host name of localhost and the first published ports: number. (If you're using the older Docker Toolbox setup, use the docker-machine ip address of the Docker VM; if you're connecting from a different host, use the Docker host's DNS name or IP address.)
# connect to pg1
psql -h localhost -p 5432 -U postgres
# connect to pg2
psql -h localhost -p 5433 -U postgres
You do not need to expose: ports in the docker-compose.yml file; this doesn't really actually do anything. You shouldn't need to reconfigure the stock postgres image beyond its basic environment-variable settings. It doesn't make sense to connect to 0.0.0.0, a special address that means "everywhere" when you're setting up a network listener.
If you're connecting from a different container, none of this matters. Use the Compose service name of the other container (like pg2) and the standard port number (5432). ports: are completely ignored, and localhost means "this container". The two containers must be on the same Docker network; Compose will create a network named default and just using that without explicit networks: settings is fine.