Why production patterns matter in Docker - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the base image in a Dockerfile.

Docker

FROM [1]

Drag options to blanks, or click blank then click option'

Aubuntu:latest

BRUN apt-get update

CCOPY . /app

DCMD python app.py

Attempts:

3 left

💡 Hint

Common Mistakes

Using commands like RUN or COPY instead of a base image.

The FROM instruction sets the base image for the Docker container. Here, ubuntu:latest is a valid base image.

2fill in blank

medium

Complete the code to expose port 80 in the Dockerfile.

Docker

EXPOSE [1]

Drag options to blanks, or click blank then click option'

A443

B80

C22

D8080

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing ports like 22 (SSH) or 443 (HTTPS) when HTTP port 80 is needed.

The EXPOSE instruction tells Docker which port the container listens on. Port 80 is the standard HTTP port.

3fill in blank

hard

Fix the error in the Dockerfile command to run the app.

Docker

CMD ["python", "[1]"]

Drag options to blanks, or click blank then click option'

Aapp.py

Brun.py

Cstart.sh

Dinstall.sh

Attempts:

3 left

💡 Hint

Common Mistakes

Using setup or install scripts instead of the main app script.

The CMD runs the main application. Here, app.py is the correct script to start.

4fill in blank

hard

Fill both blanks to create a volume mount and set environment variable in docker run command.

Docker

docker run -v [1] -e [2]=production myapp

Drag options to blanks, or click blank then click option'

A/host/data:/data

BDEBUG

CENV

D/data:/host/data

Attempts:

3 left

💡 Hint

Common Mistakes

Reversing host and container paths in volume mount.

Using wrong environment variable names.

The -v option mounts the host directory /host/data to container's /data. The -e sets environment variable ENV to 'production'.

5fill in blank

hard

Fill all three blanks to write a Dockerfile snippet that copies files, installs dependencies, and runs the app.

Docker

COPY [1] /app
RUN pip install [2]
CMD ["python", "[3]"]

Drag options to blanks, or click blank then click option'

A.

B-r requirements.txt

Capp.py

Dsrc

Attempts:

3 left

💡 Hint

Common Mistakes

Copying wrong folder path.

Forgetting the '-r' flag in pip install.

Running wrong script name.

COPY . /app copies current folder to /app in container. RUN pip install -r requirements.txt installs dependencies. CMD ["python", "app.py"] runs the app.

Practice

1. Why is it important to use production patterns like health checks and restart policies in Docker containers?

easy

A. They prevent the container from using any network resources.

B. They make the container images larger and slower to start.

C. They help keep the app running smoothly and recover from failures automatically.

D. They disable logging to improve performance.

Solution

1. Step 1: Understand the purpose of production patterns

   Production patterns like health checks and restart policies are designed to keep apps running reliably by detecting problems and restarting containers if needed.

2. Step 2: Analyze the effects of these patterns

   These patterns do not slow down containers or disable networking/logging; instead, they improve stability and uptime.

3. Final Answer:

   They help keep the app running smoothly and recover from failures automatically. -> Option C

4. Quick Check:

   Production patterns = Reliable app running [OK]

Hint: Production patterns improve reliability and auto-recovery [OK]

Common Mistakes:

• Thinking production patterns slow down containers
• Believing they disable networking or logging
• Ignoring the role of health checks

2. Which of the following Docker Compose service definitions correctly adds a restart policy for production use?

easy

A. restart: on-failure 5

B. restart: never

C. restart: sometimes

D. restart: always

Solution

1. Step 1: Review Docker restart policies

   Valid restart policies include 'no', 'always', 'on-failure', and 'unless-stopped'. 'always' restarts the container whenever it stops.

2. Step 2: Identify correct syntax

   'restart: always' is valid and commonly used in production. 'restart: never' is invalid, 'sometimes' is not a valid policy, and 'on-failure 5' is incorrect syntax (should be 'on-failure:5' for max retries).

3. Final Answer:

   restart: always -> Option D

4. Quick Check:

   Valid restart policy = restart: always [OK]

Hint: Use 'restart: always' for reliable container restarts [OK]

Common Mistakes:

• Using invalid restart policies like 'sometimes'
• Incorrect syntax for max retry counts
• Confusing 'never' with 'no'

3. Given this Dockerfile snippet for a production app:

HEALTHCHECK --interval=30s --timeout=5s CMD curl -f http://localhost/health || exit 1
CMD ["./start-app.sh"]

What happens if the health check fails repeatedly?

medium

A. Docker marks the container as unhealthy but does not restart it automatically.

B. Docker automatically restarts the container immediately.

C. The container stops running and exits.

D. Docker ignores the health check failures.

Solution

1. Step 1: Understand Docker health checks

   Health checks monitor container health and mark status as healthy or unhealthy based on the command result.

2. Step 2: Analyze restart behavior

   Docker does not restart containers automatically on health check failure unless combined with a restart policy. Health check failure only changes status.

3. Final Answer:

   Docker marks the container as unhealthy but does not restart it automatically. -> Option A

4. Quick Check:

   Health check failure = unhealthy status only [OK]

Hint: Health checks mark status; restart needs policy [OK]

Common Mistakes:

• Assuming health check failure triggers restart automatically
• Thinking container stops on health check failure
• Ignoring the need for restart policies

4. You have a Docker Compose file with this service:

web:
  image: myapp:latest
  restart: on-failure
  healthcheck:
    test: curl -f http://localhost/health || exit 1
    interval: 1m
    retries: 3

The container keeps restarting even though the app is healthy. What is the likely cause?

medium

A. The restart policy triggers on container exit, not health check failure.

B. The health check command syntax is invalid and causes failure.

C. The interval is too long, so health checks are ignored.

D. Docker Compose does not support health checks.

Solution

1. Step 1: Understand restart policy behavior

   'restart: on-failure' restarts containers only if they exit with an error, not based on health check status.

2. Step 2: Analyze health check impact

   Health check failures mark container unhealthy but do not cause restarts. If container restarts, it likely exited unexpectedly.

3. Final Answer:

   The restart policy triggers on container exit, not health check failure. -> Option A

4. Quick Check:

   Restart on-failure = restart on exit only [OK]

Hint: Restart on-failure restarts only on exit, not health check [OK]

Common Mistakes:

• Confusing health check failure with container exit
• Assuming Docker Compose ignores health checks
• Misreading health check syntax

5. You want to deploy a multi-container Docker app in production with these goals:
- Automatically restart containers on failure
- Monitor container health and alert if unhealthy
- Ensure containers start in correct order

Which combination of Docker Compose features best achieves this?

hard

A. Use restart: no, no healthcheck, and depends_on without conditions

B. Use restart: always, healthcheck with retries, and depends_on with condition: service_healthy

C. Use restart: on-failure, healthcheck without retries, and no depends_on

D. Use restart: unless-stopped, healthcheck with interval 1h, and depends_on with condition: service_started

Solution

1. Step 1: Choose restart policy for automatic recovery

   'restart: always' ensures containers restart on any stop, improving reliability.

2. Step 2: Configure health checks with retries

   Health checks with retries detect unhealthy containers and allow alerting or action.

3. Step 3: Use depends_on with service_healthy condition

   This ensures containers start only after dependencies are healthy, maintaining correct order.

4. Final Answer:

   Use restart: always, healthcheck with retries, and depends_on with condition: service_healthy -> Option B

5. Quick Check:

   Restart + healthcheck + depends_on healthy = production pattern [OK]

Hint: Combine restart, healthcheck, and depends_on with health condition [OK]

Common Mistakes:

• Skipping health checks or retries
• Using depends_on without health condition
• Choosing restart policies that don't restart on all failures