Docker events monitoring - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Understanding Docker events output

What is the output of the command docker events --filter 'event=start' --since 1m --until 0m if a container named webapp started exactly 30 seconds ago?

Docker

docker events --filter 'event=start' --since 1m --until 0m

A No output because the container started before 1 minute ago

B 2024-06-01T12:00:30.000000000Z container start webapp (container_id)

C 2024-06-01T12:00:30.000000000Z container stop webapp (container_id)

D Error: invalid filter syntax

💡 Hint

The command filters events for container start within the last minute.

The command shows events filtered by 'start' event type between 1 minute ago and now. Since the container started 30 seconds ago, its start event appears.

🧠 Conceptual

intermediate

Purpose of Docker events monitoring

Which of the following best describes the main purpose of using docker events in a DevOps workflow?

A To build Docker images from a Dockerfile

B To remove unused Docker volumes and networks

C To list all running containers with their resource usage

D To monitor real-time changes and lifecycle events of Docker objects like containers and images

💡 Hint

Think about what events represent in Docker.

Docker events provide a live stream of changes such as container start, stop, create, and destroy, which helps track Docker object states.

❓ Troubleshoot

advanced

Troubleshooting missing Docker events

You run docker events --filter 'container=webapp' but see no events even though the container is actively restarting. What is the most likely reason?

A The container name filter is case-sensitive and the actual container name is 'WebApp'

B Docker daemon is not running, so no events are generated

C The <code>docker events</code> command only shows image events, not container events

D The container is restarting too fast and events are missed by the command

💡 Hint

Check the exact container name spelling and case.

Docker filters are case-sensitive. If the container name filter does not exactly match, no events appear.

🔀 Workflow

advanced

Automating alert on container stop event

Which command pipeline correctly monitors Docker events and sends an alert message when any container stops?

A docker events --filter 'event=stop' | while read line; do echo "Alert: Container stopped - $line"; done

B docker ps --filter 'status=stopped' | echo "Alert: Container stopped"

C docker logs --follow | grep 'stopped' | echo "Alert: Container stopped"

D docker events --filter 'event=stop' --quiet

💡 Hint

Think about streaming events and reacting to each line.

Option A streams stop events and processes each line to print an alert message. Others either do not stream events or do not produce alerts.

✅ Best Practice

expert

Efficient Docker events monitoring in production

What is the best practice to efficiently monitor Docker events in a production environment without losing events during high load?

A Poll 'docker ps' every second to detect container state changes instead of using events

B Run 'docker events' with no filters and parse output manually in a shell script

C Use a dedicated logging driver like 'json-file' or 'syslog' combined with a centralized log collector instead of relying solely on 'docker events' CLI

D Restart the Docker daemon frequently to clear event buffers and avoid overload

💡 Hint

Consider reliability and scalability of event monitoring.

Using logging drivers with centralized log collection ensures no events are lost and supports high load better than CLI streaming alone.