Canary deployment pattern in Docker - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the Docker command to run a container with a specific image tag for canary deployment.

Docker

docker run -d --name canary_app [1] myapp:canary

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

A-p 8080:80

B--rm

C-it

D--network host

Attempts:

3 left

💡 Hint

Common Mistakes

Using --rm removes the container after it stops, which is not suitable for a running canary.

Using -it is for interactive mode, not needed here.

Using --network host bypasses port mapping, which is less flexible.

The -p 8080:80 option maps port 8080 on the host to port 80 in the container, allowing access to the canary deployment.

2fill in blank

medium

Complete the Docker Compose service definition to deploy a canary version of the app with limited replicas.

Docker

services:
  app_canary:
    image: myapp:canary
    deploy:
      replicas: [1]

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

A10

B0

C2

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Setting replicas to 0 means no containers run.

Setting replicas to 10 or 5 is too large for a canary.

Setting replicas to 2 allows a small portion of traffic to be served by the canary version, which is typical for canary deployments.

3fill in blank

hard

Fix the error in the Docker command to update the canary container with a new image version.

Docker

docker container [1] canary_app myapp:canary_v2

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

Aupdate

Bexec

Crun

Drestart

Attempts:

3 left

💡 Hint

Common Mistakes

docker container update does not update the image used by the container.

docker container run creates a new container, not update existing.

docker container exec runs a command inside a running container.

The docker container restart command restarts the container, which is needed after updating the image locally to apply changes.

4fill in blank

hard

Fill both blanks to create a Docker Compose snippet that routes 10% of traffic to the canary service using labels.

Docker

services:
  app_canary:
    image: myapp:canary
    deploy:
      replicas: 2
      labels:
        - "traefik.weight=[1]"
  app_stable:
    image: myapp:stable
    deploy:
      replicas: 8
      labels:
        - "traefik.weight=[2]"

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

A1

B9

C10

D90

Attempts:

3 left

💡 Hint

Common Mistakes

Using weights that do not add up proportionally to 100.

Assigning higher weight to canary than stable.

Setting traefik.weight=1 for canary and traefik.weight=90 for stable routes roughly 10% traffic to canary and 90% to stable.

5fill in blank

hard

Fill all three blanks to define a Docker Compose healthcheck that retries 3 times with 5 seconds interval for the canary service.

Docker

services:
  app_canary:
    image: myapp:canary
    healthcheck:
      test: ["CMD", "curl", "-f", "http://localhost/[1]"]
      interval: [2]s
      retries: [3]

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

Ahealth

B10

C3

D5

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong endpoint path in test command.

Setting interval or retries to zero or too high values.

The healthcheck tests the /health endpoint, retries 3 times, and waits 5 seconds between attempts to ensure the canary is healthy before routing traffic.

Practice

1.

What is the main goal of a canary deployment in Docker?

easy

A. To update a small number of containers first to reduce risk

B. To update all containers at once for faster deployment

C. To delete old containers before deploying new ones

D. To run containers without any updates

Solution

1. Step 1: Understand canary deployment purpose

   Canary deployment updates only a few containers initially to test changes safely.

2. Step 2: Compare options

   Only To update a small number of containers first to reduce risk describes updating a small number of containers to reduce risk, which matches the canary deployment goal.

3. Final Answer:

   To update a small number of containers first to reduce risk -> Option A

4. Quick Check:

   Canary deployment = update few containers first [OK]

Hint: Canary means small test update first, not all at once [OK]

Common Mistakes:

• Thinking canary updates all containers simultaneously
• Confusing canary with blue-green deployment
• Assuming canary deletes old containers immediately

2.

Which Docker command option controls how many containers update at the same time during a canary deployment?

docker service update --help

easy

A. --replicas

B. --update-delay

C. --update-parallelism

D. --rollback

Solution

1. Step 1: Identify update control options

   Docker's --update-parallelism controls how many containers update simultaneously.

2. Step 2: Differentiate from other options

   --update-delay controls wait time between updates, --replicas sets container count, and --rollback reverts updates.

3. Final Answer:

   --update-parallelism -> Option C

4. Quick Check:

   Parallelism = containers updated at once [OK]

Hint: Parallelism means how many update together [OK]

Common Mistakes:

• Confusing delay with parallelism
• Using replicas to control update speed
• Thinking rollback controls update count

3.

Given the command:

docker service update --image myapp:v2 --update-parallelism 2 --update-delay 10s myservice

What happens during this update?

medium

A. Two containers update to v2, then wait 10 seconds before next two

B. Update fails because of wrong syntax

C. One container updates every 10 seconds until all are updated

D. All containers update to v2 immediately

Solution

1. Step 1: Analyze update-parallelism

   It sets 2 containers to update at the same time.

2. Step 2: Analyze update-delay

   It waits 10 seconds between each batch of updates.

3. Final Answer:

   Two containers update to v2, then wait 10 seconds before next two -> Option A

4. Quick Check:

   Parallelism=2 + Delay=10s means batch update with wait [OK]

Hint: Parallelism sets batch size; delay sets wait time [OK]

Common Mistakes:

• Assuming all containers update instantly
• Confusing delay as total update time
• Thinking syntax is incorrect

4.

What is wrong with this command for canary deployment?

docker service update --image myapp:v2 --update-parallelism 0 --update-delay 5s myservice

medium

A. Delay cannot be less than 10 seconds

B. Service name must come before options

C. Image version syntax is incorrect

D. Parallelism cannot be zero; it must be at least 1

Solution

1. Step 1: Check update-parallelism value

   Parallelism controls how many containers update at once and must be at least 1.

2. Step 2: Validate other options

   Delay of 5s is valid; image syntax and option order are correct.

3. Final Answer:

   Parallelism cannot be zero; it must be at least 1 -> Option D

4. Quick Check:

   Parallelism=0 invalid, must be ≥1 [OK]

Hint: Parallelism must be ≥1, zero disables updates [OK]

Common Mistakes:

• Setting parallelism to zero to pause updates
• Thinking delay must be ≥10s
• Misordering command options

5.

You want to deploy a new version of your app with canary deployment using Docker Swarm. You have 10 replicas. You want to update 3 containers at a time, wait 15 seconds between batches. Which command correctly implements this?

hard

A. docker service update --image myapp:v2 --update-parallelism 3 --update-delay 15s --rollback-condition on-failure myservice

B. docker service update --image myapp:v2 --update-parallelism 3 --update-delay 15s myservice

C. docker service update --image myapp:v2 --update-parallelism 3 --update-delay 15s --rollback-on-failure myservice

D. docker service update --image myapp:v2 --update-parallelism 3 --update-delay 15s --rollback myservice

Solution

1. Step 1: Identify correct canary options

   --update-parallelism 3 and --update-delay 15s correctly set batch size and delay; no other flags needed.

2. Step 2: Verify update options

   These match exactly in docker service update --image myapp:v2 --update-parallelism 3 --update-delay 15s myservice.

3. Step 3: Check options in each command

   --rollback-condition and --rollback-on-failure are invalid; --rollback forces rollback instead of update.

4. Final Answer:

   docker service update --image myapp:v2 --update-parallelism 3 --update-delay 15s myservice -> Option B

5. Quick Check:

   Parallelism + delay with valid flags only [OK]

Hint: Parallelism sets batch size; delay sets wait; avoid invalid flags [OK]

Common Mistakes:

• Adding invalid rollback flags
• Missing parallelism or delay options
• Assuming rollback must be specified