Connecting to Postgres in docker-compose

Yes, you can reference containers by their service names, no numeric extension should be added, the name should be exactly as it is defined in docker-compose.yml.

port option is for just exposing the container port to your host, the option port: "5432" will expose port 5432 from the container on your host on 5432.

I would recommend checking that your host 5432 port is free, otherwise map to a different port:

ports:
      - "5432:5433"

Also ensure that you are not connecting to some already exsting volumes with some strange Postgres configurations, a clean postgres/postgis container will always serve on port 5432 by default.

The last and the first thing I should have mentioned is to check that the database container has started as expected, it can happen that it will not start if it’s missing some mandatory configuration options (like username), you should have logs that it started accepting clients on port 5432.

That’s the thing: the port seems to be ignored. Each time I bring up the stack, postgres is binding to a new port. There is not a conflict that I can see, i.e.

lsof -i -P | grep -i "listen"

shows nothing bound to port 5432.

When I re-run docker-compose up, the images come up including the postgres image, but it binds to a seemingly random port, e.g. 59716.

The hostname does not seem to apply… I can connect to postgres using my db client using localhost as the hostname (and whatever random port it binds to). Using db or db-1 gets an error, e.g. getaddrinfo ENOTFOUND db. Maybe that hostname is only available to the containers themselves and not to the host OS?

I’m thinking next steps for me is to try ditching docker-compose and try spinning up the needed services as simple docker conainters (without docker-compose). But I am stymied.

You sure your setting your ports correctly? BTW the setting should be ports not port in your compose file (as implied by your first post). Also make sure you’ve got the external and internal ports configured if you want to access it via localhost. For example:

    ports:
      - "5432:5432"

If you’re still having issues, then let’s see that compose file.

I’m literally just trying to kick the official tires: broadway_bike_sharing_rabbitmq_example/docker-compose.yml at main · elixir-broadway/broadway_bike_sharing_rabbitmq_example · GitHub

You are only specifying the container port (i.e. the port that the container is listening on). When that is done then the host port (the port that your machine will be listening on to be able to connect you to the DB) will be chosen randomly.

As @arcanemachine points out, you need to specify both ports if you want full control. Example:

    ports:
      - "6000:5432"

This will make PostgreSQL accessible from your dev machine on port 6000, while the DB container will listen on 5432. Docker will make a tunnel so when you connect to localhost:6000 you will be actually connecting to db:5432. Which means that you can do this from your dev machine / host:

psql -U postgres -h localhost -p 6000 postgres --command 'SELECT version();'

…and it should work. If you have a password set then just prepend PGPASSWORD=123 in front of the above command.

Source: Define services in Docker Compose | Docker Docs

Thanks. This is coming back to me. It makes sense. Seems like we might need a PR for updating that example repo? Maybe it only works if you start the app from inside the docker container

I’ve just ran the docker-compose and everything works as expected from the standpoint of database. It’s a very strange setup, but it works as expected without any issues.

What OS are you using? I’ve ran the example on ubuntu.

The only thing to keep in mind is that ecto migrations are not ran automatically, so you have to execute this command before starting the compose:

docker-compose run app mix setup

I just tried re-cloning this repo and I’m still seeing the same problems… docker-compose up brings up 2/3 of the containers – there are a bunch of db connection errors:

[error] Postgrex.Protocol (#PID<0.294.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (db:5432): connection refused - :econnrefused

docker-compose run app mix setup also generates errors. What exactly are you running?

I’m on Mac OS 14.6.1

Just installed docker desktop on my mac and everything works. There is most probably an issue with your installation.

I’ve ran the following commands (note the usage of docker compose, the old command docker-compose is deprecated from long ago):

# Just because I am too lazy to setup the rabbitmq queue manually, 
# you should get errors that tables don't exist from app, 
# close after it runs for a few seconds
docker compose up 

docker compose run app mix setup
docker compose up

I’ve used such docker-compose setups a lot of times in production and there is nothing wrong with it, most probably you have some installation issues on your machine.

Can you try connecting to the host IP+port with psql, just to make sure that you actually can reach the DB? You can also run docker ps just to make sure as well.