Flyway connection failing, connecting using psql command line works fine - docker

Question

I have a docker service for postgres that is running fine:
postgres:
restart: always
image: postgres:13.0-alpine
ports:
- "5432:5432"
environment:
- DEBUG=false
- POSTGRES_DB=yola
- POSTGRES_PASSWORD=password123
I can connect fine using terminal like this:
export PGPASSWORD=password123; psql -h localhost -p 5432 -d yola -U postgres
Now when I try and run flyway I get a connection problem.
I tried doing both 0.0.0.0 and localhost and the docker image name yola_postgres_1.
I still get this error running the following command:
docker run --rm -v /path/to/folder/migrations:/flyway/sql flyway/flyway -url=jdbc:postgresql://localhost:5432/yola -user=postgres -password=password123 info
ERROR: Unable to obtain connection from database
(jdbc:postgresql://localhost:5432/yola) for user 'postgres':
Connection to localhost:5432 refused. Check that the hostname and port
are correct and that the postmaster is accepting TCP/IP connections.
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- SQL State : 08001 Error Code : 0 Message : Connection to
localhost:5432 refused. Check that the hostname and port are correct
and that the postmaster is accepting TCP/IP connections.
Caused by: org.postgresql.util.PSQLException: Connection to
localhost:5432 refused. Check that the hostname and port are correct
and that the postmaster is accepting TCP/IP connections. Caused by:
java.net.ConnectException: Connection refused (Connection refused)

Answer 1

The Problem
You have PostgreSQL running in one container and Flyway in another, and localhost is per container, so Flyway isn't communicating with PostgreSQL
A Solution
You already map 5432 in PostgreSQL to 5432 on the host, so you can add --network=host to the docker run command for the Flyway container which makes localhost match that of the host
This will make your current set up work, and you could then look into container networking if you want your containers to communicate with each other directly, not through the host