Dashboard

We demonstrate how apps can connect to databases using the following config.

docker compose up app
# navigate to localhost:8050

Defining a local SQL database

This service references the following local_db service

  local_db:
    image: postgres
    restart: always
    volumes:
      - pgdata:/var/lib/postgresql/data/
    environment:
      POSTGRES_USER: ${DB_USER_LOCAL}
      POSTGRES_PASSWORD: ${DB_PASS_LOCAL}
      POSTGRES_DB: ${DB_NAME_LOCAL}
      TZ: ${TZ}
      POSTGRES_HOST_AUTH_METHOD: trust
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "${DB_HOST_LOCAL}"]
      interval: 5s
      timeout: 1s
      retries: 10
    healthcheck:
      test:
        [
          "CMD-SHELL",
          "pg_isready -U ${DB_USER_LOCAL} -d ${DB_NAME_LOCAL} -h ${DB_HOST_LOCAL} -p ${DB_PORT_LOCAL}",
        ]
      interval: 10s
      timeout: 5s
      retries: 5
    hostname: ${DB_HOST_LOCAL}

volumes:
  pgdata:

The local_db instance uses the named volume pgdata. This way, changes to the database will persist whenever we restart the container.

Note

Container data gets wiped every time you bring down a service!

Connecting to the database

Docker compose's DNS allows the host name for the local database to automatically match the service name. This is super convenient because we don't need to keep track of ip addresses explicitly.

  app:
    image: my-flask-app:latest
    build:
      context: app
      dockerfile: app.Dockerfile
    depends_on:
      - local_db
    environment:
      - DB_HOST=local_db
      - DB_PORT=${DB_PORT_LOCAL}
      - DB_USER=${DB_USER_LOCAL}
      - DB_PASS=${DB_PASS_LOCAL}
      - DB_NAME=${DB_NAME_LOCAL}
    volumes:
      - ./app:/usr/src/app
    depends_on:
      - local_db
    ports:
      - "8050:8050"

Here is how the app uses the environment variables to connect to the database

from sqlalchemy import create_engine
# Create an engine for connecting to the PostgreSQL database
engine = create_engine(
    f'postgresql://{DB_USER}:{DB_PASS}@{DB_HOST}:{DB_PORT}/{DB_NAME}',
    pool_size=10,  # Adjust pool_size and max_overflow to your needs
    max_overflow=20
)

When you run the app, you'll see output in the terminal

connecting to db at: postgresql://postgres_user:****@local_db:5432/postgres

We can embed the dashboard as an iframe. Because we are accessing the app from the host, we need to use localhost:

<iframe src="http://localhost:8050" width="1400" height="1200"></iframe>