Rolling updates in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the command to update a service with a rolling update in Docker Swarm.

Docker

docker service update --[1] my_service

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

Apublish

Bupdate-parallelism

Creplicas

Drollback

Attempts:

3 left

💡 Hint

Common Mistakes

Using --rollback instead of --update-parallelism

Confusing --replicas with update control

The --update-parallelism flag controls how many tasks are updated simultaneously during a rolling update.

2fill in blank

medium

Complete the command to set the delay between updating each task during a rolling update.

Docker

docker service update --update-[1] 10s my_service

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

Adelay

Bfailure-action

Cparallelism

Dmonitor

Attempts:

3 left

💡 Hint

Common Mistakes

Using --update-parallelism instead of delay

Confusing delay with monitor

The --update-delay flag sets the wait time between updating each task in the rolling update.

3fill in blank

hard

Fix the error in the command to rollback a service to the previous version.

Docker

docker service [1] my_service

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

Ascale

Bupdate

Crestart

Drollback

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' instead of 'rollback'

Using 'restart' which only restarts containers

The rollback command reverts the service to the previous version in Docker Swarm.

4fill in blank

hard

Fill both blanks to create a command that updates a service with a max failure ratio.

Docker

docker service update --update-max-failure-[1] [2] my_service

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

Aratio

B0.2

C0.5

Dtimeout

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'timeout' instead of 'ratio' for failure control

Setting failure ratio above 1

The --update-max-failure-ratio flag sets the maximum allowed failure ratio during update. Here, 0.2 means 20% failures allowed before stopping.

5fill in blank

hard

Fill all three blanks to update a service with parallelism 2, delay 5s, and monitor 15s.

Docker

docker service update --update-parallelism [1] --update-delay [2] --update-[3] 15s my_service

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

A2

B5s

Cmonitor

Dtimeout

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing 'timeout' with 'monitor'

Using wrong time units for delay or monitor

This command sets the update parallelism to 2 tasks at once, waits 5 seconds between updates, and monitors for 15 seconds after each update.

Practice

1. What is the main purpose of a rolling update in Docker?

easy

A. To restart the Docker daemon automatically

B. To delete all containers and recreate them at once

C. To backup container data before updating

D. To update containers gradually without downtime

Solution

1. Step 1: Understand rolling update concept

   A rolling update means updating parts of a system bit by bit instead of all at once.

2. Step 2: Apply to Docker containers

   In Docker, rolling updates replace containers one by one to avoid downtime.

3. Final Answer:

   To update containers gradually without downtime -> Option D

4. Quick Check:

   Rolling update = gradual update without downtime [OK]

Hint: Rolling update means gradual replacement, not all at once [OK]

Common Mistakes:

• Thinking rolling update deletes all containers simultaneously
• Confusing rolling update with backup process
• Assuming rolling update restarts Docker daemon

2. Which Docker command option is used to perform a rolling update on a service?

easy

A. docker service update --rolling-update

B. docker service update --rollback

C. docker service update --update-parallelism

D. docker service update --force

Solution

1. Step 1: Identify rolling update options

   Docker uses --update-parallelism to control how many containers update at once.

2. Step 2: Match option to rolling update

   This option allows gradual updates, which is the essence of rolling updates.

3. Final Answer:

   docker service update --update-parallelism -> Option C

4. Quick Check:

   Rolling update option = --update-parallelism [OK]

Hint: Use --update-parallelism to control rolling update speed [OK]

Common Mistakes:

• Using --force which restarts all containers immediately
• Assuming --rollback triggers rolling update
• Inventing a non-existent --rolling-update flag

3. Given the command:

docker service update --image myapp:v2 --update-parallelism 2 myservice

What will happen during this update?

medium

A. All containers of myservice update at once to v2

B. Two containers update at a time to v2 until all are updated

C. Only two containers update and the rest stay on old version

D. The service rolls back to the previous version

Solution

1. Step 1: Understand --update-parallelism effect

   The option --update-parallelism 2 means update 2 containers at once.

2. Step 2: Apply to service update

   Docker updates 2 containers to image v2, then moves to next 2, until all are updated.

3. Final Answer:

   Two containers update at a time to v2 until all are updated -> Option B

4. Quick Check:

   --update-parallelism 2 means update 2 containers at once [OK]

Hint: Parallelism number controls how many containers update simultaneously [OK]

Common Mistakes:

• Thinking all containers update simultaneously
• Believing only two containers update permanently
• Confusing update with rollback

4. You run:

docker service update --image myapp:v3 --update-parallelism 3 --update-delay 10s myservice

But the update fails and leaves some containers on old version. What is a likely cause?

medium

A. The image myapp:v3 does not exist or is invalid

B. The update-delay is too short causing timeout

C. The update-parallelism value must be 1

D. Docker service update does not support update-delay

Solution

1. Step 1: Check update-delay and parallelism validity

   Both --update-delay and --update-parallelism are valid options and can be used together.

2. Step 2: Consider image availability

   If the new image myapp:v3 is missing or invalid, update fails and some containers remain old.

3. Final Answer:

   The image myapp:v3 does not exist or is invalid -> Option A

4. Quick Check:

   Update fails if new image is missing or bad [OK]

Hint: Check image existence if update leaves old containers [OK]

Common Mistakes:

• Assuming update-delay causes failure
• Thinking parallelism must be 1
• Believing update-delay is unsupported

5. You want to update a Docker service with 10 replicas using rolling updates. You want to update 3 containers at a time and wait 5 seconds between batches. Which command correctly achieves this?

hard

A. docker service update --image myapp:v2 --update-parallelism 3 --update-delay 5s myservice

B. docker service update --image myapp:v2 --update-parallelism 5 --update-delay 3s myservice

C. docker service update --image myapp:v2 --update-parallelism 10 --update-delay 0s myservice

D. docker service update --image myapp:v2 --update-delay 5s myservice

Solution

1. Step 1: Match update-parallelism to batch size

   To update 3 containers at a time, use --update-parallelism 3.

2. Step 2: Set delay between batches

   To wait 5 seconds between batches, use --update-delay 5s.

3. Step 3: Verify full command

   Combining these with the image and service name gives the correct command.

4. Final Answer:

   docker service update --image myapp:v2 --update-parallelism 3 --update-delay 5s myservice -> Option A

5. Quick Check:

   Parallelism 3 + delay 5s = correct rolling update command [OK]

Hint: Use --update-parallelism for batch size and --update-delay for wait time [OK]

Common Mistakes:

• Using wrong parallelism number
• Omitting update-parallelism option
• Setting delay but not parallelism