Setting up Elixir with Dockerized PostgreSQL

In short, in config/dev.exs change postgres_db hostname to localhost and try again - it should work:

diff --git a/config.exs b/config.exs
--- a/config.exs
+++ b/config.exs
@@ -3,3 +3,3 @@ config :weather, Weather.Repo,
   password: "postgres",
-  hostname: "postgres_db",
+  hostname: "localhost",
   port: 5432,

Actually it works for local instance of postgres but not for postgres container in docker.
I set password provided during setting up contaner, as a host (according to docs) i set up container name.

I get errors about non-existing domain.

With local Postgres everything works
With Postgres in docker I cant create database using mix ecto.create.

Is your elixir container part of that docker-compose too? If yes your configuration should work, otherwise you need to specify a custom network, as only containers from the same docker-compose are part of the same network automatically.

Actually I didnt put Elixir into container as I didn’t do anything in app. Just started and wanted to connect everything together and even meant to work with app development in container.

I meant to work directly from Windows with developing app but having it connected to containerized database. As it’s first time using docker and learning it I dont get whole concepts yet and how it should be resolved.

If your elixir application is not in container, then the only way is to expose the port and connect on localhost, just as it was mentioned previously by others.

I read a little about that but it still doesn’t work.
To create container and expose port I used command:

docker run --name postgres_db -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=postgres -p 5432:5432 -d postgres

Using those credentials and IPHost provided while inspecting container I could go into server in pgadmin4. Basically it works.

Now the part that doesn’t work with Elixir
dev.exs

config :weather, Weather.Repo,
  username: "postgres",
  password: "postgres",
  hostname: "postgres_db",
  port: 5432,
  database: "weather_dev",
  stacktrace: true,
  show_sensitive_data_on_connection_error: true,
  pool_size: 10

As you can see. Credentials are the same. Hostname is container name in this case:
Obviously i got:

14:13:27.670 [error] Postgrex.Protocol (pid<0.211.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (postgres_db:5432): non-existing domain - :nxdomain

I changed hostname to localhost:

FORMATTER ERROR: bad return value

14:14:18.846 [debug] ** (RuntimeError) bad return value from Logger formatter Logger.Formatter, got [[<<179, 101, 109, 32, 110, 105, 101, 32, 112, 111, 119, 105, 111, 100, 179, 97, 32, 115, 105, 234, 32, 100, 108, 97, 32, 117, 191, 121, 116, 107, 111, 119, 110, 105, 107, 97, 32, 34, 112, 111, 115, 116, 103, 114, 101, 115, 34>>, “\n”] | “\e[0m”] after “\e[31m\n14:14:18.843 [error] Postgrex.Protocol (pid<0.416.0>) failed to connect: ** (Postgrex.Error) KATASTROFALNY 28P01 (invalid_password) autoryzacja has”
(kernel 9.0.2) logger_h_common.erl:430: :logger_h_common.string_to_binary/1
(kernel 9.0.2) logger_h_common.erl:396: :logger_h_common.do_log_to_binary/2
(kernel 9.0.2) logger_h_common.erl:177: :logger_h_common.log/2
(kernel 9.0.2) logger_backend.erl:51: :logger_backend.call_handlers/3
(db_connection 2.6.0) lib/db_connection/connection.ex:110: DBConnection.Connection.handle_event/4
(stdlib 5.0.2) gen_statem.erl:1379: :gen_statem.loop_state_callback/11
(stdlib 5.0.2) proc_lib.erl:241: :proc_lib.init_p_do_apply/3

FORMATTER ERROR: bad return value

14:14:18.881 [debug] ** (RuntimeError) bad return value from Logger formatter Logger.Formatter, got [[<<179, 101, 109, 32, 110, 105, 101, 32, 112, 111, 119, 105, 111, 100, 179, 97, 32, 115, 105, 234, 32, 100, 108, 97, 32, 117, 191, 121, 116, 107, 111, 119, 110, 105, 107, 97, 32, 34, 112, 111, 115, 116, 103, 114, 101, 115, 34>>, “\n”] | “\e[0m”] after “\e[31m\n14:14:18.881 [error] Postgrex.Protocol (pid<0.424.0>) failed to connect: ** (Postgrex.Error) KATASTROFALNY 28P01 (invalid_password) autoryzacja has”
(kernel 9.0.2) logger_h_common.erl:430: :logger_h_common.string_to_binary/1
(kernel 9.0.2) logger_h_common.erl:396: :logger_h_common.do_log_to_binary/2
(kernel 9.0.2) logger_h_common.erl:177: :logger_h_common.log/2
(kernel 9.0.2) logger_backend.erl:51: :logger_backend.call_handlers/3
(db_connection 2.6.0) lib/db_connection/connection.ex:110: DBConnection.Connection.handle_event/4
(stdlib 5.0.2) gen_statem.erl:1379: :gen_statem.loop_state_callback/11
(stdlib 5.0.2) proc_lib.erl:241: :proc_lib.init_p_do_apply/3

** (Mix) The database for Weather.Repo couldn’t be created: killed

Error is different - result the same. No connection.
It looks like it tries to go into my local instance of postgres but there are invalid credentials for that.
I dont know how it’s supposed to be working with localhost if its signed to local machine and not docker even if i exposed port and it should be working.

I am out of ideas for a now.

Most common cause of mismatched credentials when trying to connect to PG in container is that you still have PG running on the host system and are actually connecting to that. Either shut down PG on the host and restart the container, or bind the container port to something other than 5432 (and then configure Ecto to use the new port).

And that post with addition of advices above are solutions. I had of course closed Postgres but in the background there were left some tasks. I had to kill them and then Elixir created db and schemas. Perfect.

Other port didnt work by the way, but probably because I hadn’t it opened.

Big thanks for fast reply for silly questions

Don’t know if you’ve fixed the problem, but in my case, i have the same problem using a postgres container with ruby, and i ran a container with this command:

docker run --network localhost --name postgres_db -e POSTGRES_USER=postgres -e POSTGRES_PASSWORD=postgres -p 5432:5432 -d postgres

just added --network localhost and used localhost on your config file and it should work

For local development I like to use this compose file as a template, which works well with an out of the box phoenix project.

services:
  postgres:
    image: postgres:17
    container_name: postgres
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
    volumes:
      - type: volume
        source: data
        target: /var/lib/postgresql/data
    ports:
      - name: postgres
        target: 5432
        published: 5432

volumes:
  data: