Go with Postgres and Docker - 127.0.0.11:53: no such host

I use docker compose to run my application on a VPS server. It consists of a golang backend and PostgreSQL DB. While the backend connected to the DB completely fine on my PC, it fails to do so on the VPS. I've listed host.docker.internal in the .env file, I guess the problem be somewhere there.

Error:

2024/10/15 21:18:16 /app/config/database.go:39

[error] failed to initialize database, got error failed to connect to `user=_ database=_`: hostname resolving error: lookup host.docker.internal on 127.0.0.11:53: no such host

panic: failed to connect to `user=_ database=_`: hostname resolving error: lookup host.docker.internal on 127.0.0.11:53: no such host

goroutine 1 [running]:

politex/backend/config.Connect()

    /app/config/database.go:42 +0x378

main.main()

    /app/main.go:12 +0x25

docker-compose.yml:

services:
  backend:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    depends_on:
      - db
  db:
    restart: always
    image: postgres:16.4
    ports:
      - "5432:5432"
    environment:
      POSTGRES_USER: _
      POSTGRES_PASSWORD: _
      POSTGRES_DB: _
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata:

.env:

DB_HOST=host.docker.internal
DB_PASS=_
DB_PORT=5432
DB_USER=_
DB_NAME=_

database.go:

package config

import (
    ...
)

var Database *gorm.DB

func Connect() error {
    envErr := godotenv.Load()
    if envErr != nil {
        panic(envErr)
    }

    user := os.Getenv("DB_USER")
    host := os.Getenv("DB_HOST")
    pass := os.Getenv("DB_PASS")
    name := os.Getenv("DB_NAME")
    port := os.Getenv("DB_PORT")

    dsn := fmt.Sprintf("host=%v user=%v password=%v dbname=%v port=%v sslmode=disable TimeZone=Europe/Moscow", host, user, pass, name, port)

    var err error
    Database, err = gorm.Open(postgres.Open(dsn), &gorm.Config{})

    if err != nil {
        panic(err)
    }

    Database.AutoMigrate(&entities.Note{})

    return nil
}

Solution

Solved: I did assign the static IP to the db container and added it to .env file (and yeah, setting host to "db" didn't work for some reason)

docker-compose.yml:

services:
  backend:
    build:
      context: backend
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    networks:
      - static
    depends_on:
      - db
  db:
    restart: always
    image: postgres:16.4
    ports:
      - "5432:5432"
    environment:
      POSTGRES_USER: _
      POSTGRES_PASSWORD: _
      POSTGRES_DB: _
    networks:
        static:
          ipv4_address:
            172.20.128.2
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata:
networks:
  static:
    ipam:
      config:
        - subnet: "172.20.0.0/16"

.env:

DB_HOST=172.20.128.2
DB_PASS=_
DB_PORT=5432
DB_USER=_
DB_NAME=_