Docker: Is the server running on host "localhost" (::1) and accepting TCP/IP connections on port 5432?

The issue is that you are trying to connect to localhost inside the container for DB. The port mapping that you do 5432:5432 for postgres map 5432 to localhost of your host machine.

Now your web container code is running inside the container. And there is nothing on its localhost:5432.

So you need to change your connection details in the config to connect to postgres:5432 and this is because you named the postgres DB service as postgres

Change that and it should work.

By default the postgres image is already exposing to 5432 so you can just remove that part in your yml.

Then if you would like to check if web service can connect to your postgres service you can run this docker-compose exec web curl postgres:5432 then it should return:

curl: (52) Empty reply from server

If it cannot connect it will return:

curl: (6) Could not resolve host: postgres or curl: (7) Failed to connect to postgres port 5432: Connection refused

UPDATE:

I know the problem now. It's because you are trying to connect on the localhost you should connect to the postgres service.