Rolling updates in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

💻 Command Output

intermediate

Output of a rolling update command in Docker Swarm

What is the output of the following command when updating a service with rolling update strategy in Docker Swarm?

Docker

docker service update --image nginx:1.19 my_web_service

A

my_web_service
rolling update started
3/3 tasks updated

B Error: service not found

C

my_web_service
service updated successfully

D

my_web_service
overall progress: 1 out of 3 tasks
1/3 updated, 0 tasks running

💡 Hint

Think about how Docker Swarm reports progress during rolling updates.

The docker service update command shows the progress of the rolling update, including how many tasks have been updated and how many are running.

🧠 Conceptual

intermediate

Understanding rolling update behavior in Docker Swarm

Which statement correctly describes the rolling update behavior in Docker Swarm?

A Docker Swarm updates all service tasks simultaneously, causing downtime.

B Docker Swarm updates tasks one by one, ensuring some tasks remain running during update.

C Docker Swarm stops all tasks before starting new ones to avoid conflicts.

D Docker Swarm requires manual restart of each task during update.

💡 Hint

Think about how rolling updates minimize downtime.

Rolling updates in Docker Swarm update tasks one at a time or in batches, keeping the service available during the update.

❓ Configuration

advanced

Configuring rolling update parameters in Docker service

Which Docker service update command correctly sets the rolling update to update 2 tasks at a time with a 10-second delay between updates?

A docker service update --update-parallelism 2 --update-delay 10s my_service

B docker service update --parallelism 2 --delay 10 my_service

C docker service update --update-parallel 2 --update-delay 10 my_service

D docker service update --update-parallelism=2 --update-delay=10 my_service

💡 Hint

Check the exact option names and units for delay.

The correct flags are --update-parallelism and --update-delay with the delay specified in seconds with 's'.

❓ Troubleshoot

advanced

Troubleshooting a failed rolling update in Docker Swarm

After running a rolling update, some tasks fail to start and the service is stuck updating. What is the most likely cause?

A The service has no published ports.

B The update delay is set too high.

C The new image tag does not exist or is invalid.

D The Docker daemon is running an outdated version.

💡 Hint

Think about what would prevent new tasks from starting.

If the new image tag is invalid or missing, tasks cannot start with the updated image, causing the update to fail.

🔀 Workflow

expert

Order the steps for performing a safe rolling update in Docker Swarm

Arrange the following steps in the correct order to perform a safe rolling update of a Docker Swarm service.

A 1,2,3,4

B 2,1,3,4

C 1,3,2,4

D 3,1,2,4

💡 Hint

Think about preparation, execution, monitoring, and finalizing steps.

First, ensure the new image is ready. Then update the service. Monitor the update and finally rollback if needed or confirm success.