Canary deployment pattern in Docker - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the main purpose of a canary deployment?

Choose the best description of the canary deployment pattern in software delivery.

A Run two versions of software simultaneously for load balancing

B Deploy all changes to production at once to minimize downtime

C Gradually roll out a new version to a small subset of users before full deployment

D Automatically rollback all changes after deployment without testing

💡 Hint

Think about how to reduce risk when releasing new software.

Canary deployment means releasing a new version to a small group first to catch issues early before full rollout.

💻 Command Output

intermediate

What is the output of this Docker command during canary deployment?

Given the command below, what will it show?

docker service ls --filter name=myapp_canary

A Lists all running services including the canary version named 'myapp_canary'

B Shows an error because the filter syntax is incorrect

C Lists only services not related to 'myapp_canary'

D Shows no output because no services exist

💡 Hint

Check how Docker filters services by name.

The command filters and lists services with names matching 'myapp_canary', showing the canary deployment service.

❓ Configuration

advanced

Which Docker Compose snippet correctly defines a canary deployment with 10% traffic?

Choose the correct Docker Compose service configuration to deploy a canary version receiving 10% of traffic using Docker Swarm.

Docker

version: '3.8'
services:
  web:
    image: myapp:stable
    deploy:
      replicas: 9
  web_canary:
    image: myapp:canary
    deploy:
      replicas: 1

A The snippet above correctly sets 9 stable and 1 canary replica for 10% traffic

B The canary service must have replicas: 0.1 to get 10% traffic

C The snippet should use 'mode: global' for canary to get 10% traffic

D Traffic split is controlled by 'update_config' not replicas count

💡 Hint

Think about how replica counts relate to traffic distribution in Docker Swarm.

Setting 9 replicas for stable and 1 for canary means 10% of total replicas run canary, approximating 10% traffic.

❓ Troubleshoot

advanced

Why does the canary deployment not receive any traffic despite correct replica settings?

You deployed a canary service with 1 replica alongside 9 stable replicas. However, no user traffic reaches the canary. What is the most likely cause?

A The stable service has zero replicas running

B The canary service image is missing from the registry

C Docker Swarm does not support multiple replicas

D The load balancer is not configured to route traffic to the canary service

💡 Hint

Consider how traffic routing works in a multi-service deployment.

If the load balancer routes only to stable replicas, canary replicas get no traffic despite being up.

🔀 Workflow

expert

Order the steps for a safe canary deployment using Docker and monitoring tools

Arrange these steps in the correct order to perform a canary deployment safely.

A 2,1,3,4

B 1,3,2,4

C 1,2,3,4

D 3,1,2,4

💡 Hint

Think about deploying first, then routing traffic, monitoring, and finally full rollout.

First deploy canary replicas, then route traffic to them, monitor results, and if all is good, roll out fully.