Setting up Elixir with Dockerized PostgreSQL

mbski

Hello,

I am coming back to Elixir world after one year and I wanted to learn also new stuff so I decided to use Docker to my development.

I pulled pgadmin4 and postgresql, set it up according to documentation/articles. It looks like it works fine. I can log in into pgadmin4 through docker, I can open server with credentials given for postgresql container.

Elixir works fine if I want to play with localhost - I have also desktop version of PGAdmin4 and if I use credentials and localhost I can easily create ecto database.

Problem starts when I want to use locally developed Elixir/Phoenix app with PostgreSQL which is in container. I couldn’t find anything that could have helped me resolved this.

Container name: postgres_db,
Username: postgres,
Password: admin123,
Image: postgres

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

Rest left unchanged from initially created files.

PS F:\weather> mix ecto.create
Compiling 28 files (.ex)
Generated weather app

08:05:39.563 [error] Postgrex.Protocol (pid<0.416.0>) failed to connect: ** (DBConnection.ConnectionError) tcp connect (postgres_db:5432): non-existing domain - :nxdomain
** (Mix) The database for Weather.Repo couldn’t be created: connection not available and request was dropped from queue after 2000ms. This means requests are coming in and your connection pool cannot serve them fast enough. You can address this by:

Ensuring your database is available and that you can connect to it

Tracking down slow queries and making sure they are running fast enough

Increasing the pool_size (although this increases resource consumption)

Allowing requests to wait longer by increasing :queue_target and :queue_interval

See DBConnection.start_link/2 for more information

Thats what i got when i try to create database.

I also tried to use IP address that I put while creating server in postgres, but it still times out.

My another try was also using docker-compose.yml

version: '3.8'

services:
  postgres_db:
    image: postgres
    volumes:
      - /var/lib/postgresql/data
    container_name: weather
    environment:
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
      POSTGRES_DB: weather_dev
    ports:
      - 5432:5432

Accordingly I updated dev.exs to fit those variables and stopped container created meanually (to omit port conflicts). Effect remains the same. Its not possible to connect Elixir with dockerized Postgres and I cant create database for my app.

Thanks for any help

10 comments

/phoenix #docker #postgres

1 2959 10

2025-06-24 01:09:15 UTC

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Tyson

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).

Post #7

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adamu

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:

Post #10

D4no0

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.

Post #3