Repair a Broken Nginx Container

Scenario

A teammate handed you a container that “runs but doesn’t work.” `docker ps` shows it Up, but the browser returns nothing. Find out why and get the site serving.

Learning objectives

Confirm the container is running
Identify why the site is unreachable
Correct the port mapping and/or content mount
Verify the site responds with HTTP 200

Before you start

Required software: Docker Engine 24+ or Docker Desktop

Prerequisites: Run Your First Container (or equivalent)

Download the lab archive and unzip it.
From the lab folder, start the broken environment: docker compose up -d (or run the provided start.sh).
Try to load the site at the URL the README says — it will fail; that is expected.

Instructions

1. Observe

List the container and check its ports:

docker ps
docker inspect broken-web --format '{{json .NetworkSettings.Ports}}'

2. Look inside

Check what nginx is actually serving:

docker exec broken-web ls -la /usr/share/nginx/html
docker logs broken-web

3. Fix it

There are up to three planted problems: a wrong host:container port, a content mount pointing at the wrong path, and/or a missing index file. Correct the compose file and re-apply with docker compose up -d.

4. Validate

Run the validation script and confirm HTTP 200:

bash validation/validate.sh

Hints

💡 It’s Up but nothing loads

A container can be healthy and still unreachable if the published port maps to a port nothing is listening on. Compare the -p mapping to the port nginx listens on (80).

💡 nginx serves a 403 or default page

The document root mount may point at an empty or wrong directory. Check the bind mount target against nginx’s root (/usr/share/nginx/html).

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

The full solution + troubleshooting explanation is available to signed-in learners. Try to solve it first — that’s where the learning is.

Reset the lab

docker compose down then docker compose up -d restores the broken starting state from the untouched compose file (keep a copy of the original).

Interview questions

A container is “Up” but the app is unreachable — what are the first three things you check?
How do you find which host port maps to a container’s port?
How would you confirm what files a container is actually serving?

Finished this lab?