Alert setup for container health in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding container health checks

Which of the following best describes the purpose of a HEALTHCHECK instruction in a Dockerfile?

A It specifies the network ports that the container exposes.

B It sets the container's resource limits like CPU and memory usage.

C It defines a command that Docker runs to test if the container is working properly.

D It installs monitoring software inside the container.

💡 Hint

Think about how Docker knows if a container is healthy or not.

The HEALTHCHECK instruction tells Docker how to test the container's health by running a command inside it periodically.

💻 Command Output

intermediate

Interpreting Docker container health status

What is the output of the following command if the container named webapp is healthy?

docker inspect --format='{{.State.Health.Status}}' webapp

A healthy

B unhealthy

C starting

D exited

💡 Hint

The command shows the health status of the container.

The command prints the health status of the container. If the container is healthy, it outputs healthy.

🔀 Workflow

advanced

Setting up alerting for unhealthy containers

You want to receive an alert when a Docker container becomes unhealthy. Which workflow below correctly describes the steps to achieve this using Docker events and a simple script?

A Run <code>docker events</code> to listen for container health status changes, filter for 'unhealthy' events, then trigger an alert script.

B Use <code>docker ps</code> to list containers and manually check health status every hour.

C Configure the container to send email alerts directly from inside the container when unhealthy.

D Restart the container automatically without monitoring health status.

💡 Hint

Think about how to get real-time notifications from Docker.

Docker events can be used to listen for health status changes. Filtering for 'unhealthy' events allows triggering alerts automatically.

❓ Troubleshoot

advanced

Diagnosing why a container health check fails

A container's health check keeps failing even though the service inside is running fine. Which of the following is the most likely cause?

A The container has no network access.

B The container image is missing.

C Docker daemon is not running.

D The health check command is incorrect or does not return the expected exit code.

💡 Hint

Consider what the health check command does and how Docker interprets its result.

If the health check command is wrong or returns a non-zero exit code, Docker marks the container as unhealthy even if the service is running.

✅ Best Practice

expert

Choosing the best health check command for a web server container

Which health check command is the best choice to monitor a web server running inside a Docker container?

A ping -c 1 localhost

B curl -f http://localhost:80/ || exit 1

C ps aux | grep nginx

D echo 'healthy'

💡 Hint

Think about a command that verifies the web server is responding correctly.

Using curl -f checks if the web server responds with a successful HTTP status. Other options do not verify the web service properly.