Recover a Persistent Database

Learning objectives

• Identify the correct data volume
• Back up the database
• Recreate the service
• Restore the data
• Verify row counts match

Before you start

Required software: Docker Engine 24+

Prerequisites: Docker Storage path (or Fundamentals)

1. Download and unzip the lab.
2. Start it and seed data: docker compose up -d then run the provided seed.sh.

Instructions

Hints

💡 Which volume holds the data?

docker volume ls then docker inspect the postgres container to see its mount — match the volume name to the mount target /var/lib/postgresql/data.

💡 Back up logically, not just the volume

A consistent logical backup (pg_dump) is safer than copying files from a live volume. Run pg_dump via docker exec and capture the output on the host.

Validate your work

From the lab folder, run:

bash validation/validate.sh

The script reads only your local Docker state, never transmits data off your machine, and returns a status code:

• 0 — Lab successfully completed
• 1 — Validation failed
• 2 — Required dependency missing
• 3 — Lab environment not running
• 4 — Configuration error
• 5 — Validation timed out

Note: validation targets Linux first. On Docker Desktop (macOS/Windows) some host-level checks (e.g. disk usage) may report differently; each script documents its limitations.

Solution

Reset the lab

• docker compose down -v && docker compose up -d from the original lab files restores the starting (broken) state.

Interview questions

• What’s the difference between backing up a volume’s files vs `pg_dump`?
• How do you find which volume a container uses?
• How would you verify a restore succeeded?