Resolve Docker Disk Exhaustion

Learning objectives

• Measure Docker disk usage
• Locate oversized container logs
• Identify unused images and stopped containers
• Reclaim space without touching live data
• Configure log rotation

Before you start

Required software: Docker Engine 24+ (Linux recommended)

Prerequisites: Docker Monitoring & Troubleshooting path

1. Download and unzip the lab.
2. Start it: docker compose up -d (a noisy service will generate large logs).

Instructions

Hints

💡 Where is the space going?

docker system df -v breaks usage down by images, containers, volumes, and build cache. Container logs live outside this — check /var/lib/docker/containers/*/*-json.log sizes.

💡 Prune without data loss

docker image prune (dangling) and docker container prune are safe; docker system prune --volumes is NOT — it can delete named volumes with real data. Be specific.

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 does `docker system df` show and how do you get per-object detail?
• Which prune commands are safe on a production host and which are dangerous?
• How do you cap a container’s log size?