Deployment

Rationale for some deployment choices.

Why Use Docker?

• Consistency - development matches the production environment
• Isolation - avoid polluting the host system with dependencies & avoid errors in the application due to changes in software installed on host system
• Reproducibility & Portability - anyone can create the exact same environment
• Quick Reset - can destroy and rebuild everything quickly

Downsides of using Docker:

• Some overhead, 2 - 5% performance penalty
• Extra complexity, such as exposing ports

Explanation of docker-compose lines

In the docker-compose.yml file, the lines:

    volumes:
      - db_data:/var/lib/postgresql/data
      - ./db/init.sql:/docker-entrypoint-initdb.d/init.sql

• - db_data:/var/lib/postgresql/data

db_data is a named volume managed by Docker, not a host path. /var/lib/postgresql/data is a directory inside the Postgres container where Postgres database files are stored.

Where is the database? On the host's file system, the volume is stored in Docer's internal storage, i.e. /var/lib/docker/volumes on Linux. Its not in the project directory.

Inspecting the Volume

On Linux use:

docker volume ls
docker volume inspect homelog_db_data

• - ./db/init.sql:/docker-entrypoint-initdb.d/init.sql

is a bind mount that instruct Docker to copy a file (db/init.sql) from the host filesystem into the PostgreSQL container.

/docker-entrypoint-initdb.d/init.sql is a special location. When you start a Postgres contain, if the data volume is empty the container will

1. create the specified database (homelog)
2. Look in /docker-entrypoint-initdb.d/ for any .sql, .sql.gz, or .sh files.
3. Execute all the files in alphabetical order.

Hence, the script runs only if the database volume is empty.
Useful for development, but for a production environment it is better to manage the schema and data using migrations, e.g. Alembic with SQLAlchemy.

Running A Container Locally

1. Start the "db" service:

   docker compose up -d db

   or start with dependencies:

   docker compose up -d db init-script

2. Verify it's running:

   docker ps

3. Interact with it:

   • pgsql command line
   • Database browser such as DBeaver

4. Stop it, using id prefix or container name.

   docker container ls
   docker stop [ a1b2c3d4 | homelog-db-1 ]

5. View log files (specify container name)

   docker logs homelog-db-1

6. docker-compose projects, stop & remove container:

   • Stop container and remove it: docker compose down
   • Also remove volumes: docker compose down --volumes

Supabase for Database

What version of Postgres is Supabase using?

On Supabase I used the SQL Editor to query the database version. Response was (15 Jun 2025):

PostgreSQL 17.4 on aarch64-unknown-linux-gnu, compiled by gcc (GCC) 13.2.0, 64-bit