PostgreSQL in Docker

Running with Persistent Storage

Postgres keeps everything under one directory, so mounting that directory is non-negotiable:

docker run -d --name pg \
  -e POSTGRES_PASSWORD=devpass \
  -e POSTGRES_DB=app \
  -v pgdata:/var/lib/postgresql/data \
  -p 5432:5432 \
  postgres:16

The entrypoint initializes the cluster on first boot, creates the database, and starts the server on 5432. Pair it with a health check the orchestrator can consume:

docker exec pg pg_isready -U postgres

Without the named volume, docker rm destroys the cluster with the container — the classic way to lose a demo dataset.

Configuration for Containers

Container Postgres shares RAM with the app, so defaults sized for a dedicated host are wrong. Override at launch or via a mounted config:

docker run -d --memory 2g postgres:16 \
  -c shared_buffers=512MB \
  -c max_connections=100 \
  -c effective_cache_size=1536MB

Common starting points: shared_buffers near a quarter of container memory, effective_cache_size describing what the OS cache is expected to contribute, and max_connections sized below what the pooler and memory allow — connection storms are better absorbed by PgBouncer than by raising the limit. Persist settings with -c flags or an postgresql.conf mount, never by exec-ing ALTER SYSTEM that no one can review.

Backups and Pitfalls

Logical backups run inside the container:

docker exec pg pg_dump -U postgres -Fc app > app.dump
docker exec -i pg pg_restore -U postgres -d app_recovered < app.dump

-Fc (custom format) supports parallel restore and selective -t table recovery. Schedule it from the host, not from a container that dies with the cluster.

Pitfalls. Files in /docker-entrypoint-initdb.d run only when the data directory is empty — schema edits to them silently do nothing on a live volume. fsync=off speeds bulk loads but can corrupt after a hard stop: dev-only.

Interview: walk first-boot initialization, name the volume path you protect, and contrast pg_dump with physical base backups for point-in-time recovery.