Why Canary deployments in Kubernetes? - Purpose & Use Cases

The Big Idea

What if you could update your app without risking a full crash for all users?

The Scenario

Imagine you just updated your app and want to see if users like it. You change the whole app for everyone at once. If something breaks, all users see errors and get frustrated.

The Problem

Changing everything at once is risky and scary. If the new version has bugs, you must fix it fast or lose users. Manually switching versions takes time and can cause mistakes, making downtime longer.

The Solution

Canary deployments let you send the new version to just a small group of users first. You watch how it works, catch problems early, and only then release it to everyone. This way, you reduce risk and keep users happy.

Before vs After

✗ Before

kubectl set image deployment/myapp myapp=myapp:v2

✓ After

kubectl apply -f canary-deployment.yaml
# Sends new version to 10% of users first

What It Enables

Canary deployments make releasing updates safer and smoother by testing changes on a small scale before full rollout.

Real Life Example

A streaming service uses canary deployments to update their video player. They send the new player to 5% of users first. If no issues appear, they gradually increase the rollout, avoiding crashes for everyone.

Key Takeaways

Manual full updates risk breaking the whole app at once.

Canary deployments test new versions on a small user group first.

This approach reduces errors and improves user experience during updates.

Practice

1. What is the main purpose of a canary deployment in Kubernetes?

easy

A. To release a new version to a small group of users first to reduce risk

B. To deploy all users to the new version immediately

C. To delete the old version before deploying the new one

D. To run multiple versions permanently without any rollout

Solution

1. Step 1: Understand canary deployment concept

   Canary deployments release new software versions to a small subset of users first to test stability and reduce risk.

2. Step 2: Compare options with this concept

   Only To release a new version to a small group of users first to reduce risk describes this gradual rollout to a small group to reduce risk.

3. Final Answer:

   To release a new version to a small group of users first to reduce risk -> Option A

4. Quick Check:

   Canary deployment = gradual rollout [OK]

Hint: Canary means small test group rollout first [OK]

Common Mistakes:

• Thinking canary deploys to all users at once
• Confusing canary with blue-green deployment
• Assuming canary deletes old versions immediately

2. Which Kubernetes resource is typically used to manage canary deployments?

easy

A. Deployment

B. ConfigMap

C. ServiceAccount

D. PersistentVolume

Solution

1. Step 1: Identify resource for managing app versions

   Deployments manage application versions and rollout strategies in Kubernetes.

2. Step 2: Match resource to canary deployment

   Canary deployments use multiple Deployments with different labels to control traffic.

3. Final Answer:

   Deployment -> Option A

4. Quick Check:

   Canary uses Deployment resource [OK]

Hint: Deployments control app versions and rollout [OK]

Common Mistakes:

• Choosing ConfigMap which stores config, not versions
• Selecting ServiceAccount which manages permissions
• Picking PersistentVolume which handles storage

3. Given this snippet of a Kubernetes Deployment YAML for canary rollout, what percentage of traffic will go to the canary pods?

apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-canary
  labels:
    version: canary
spec:
  replicas: 2
  selector:
    matchLabels:
      app: myapp
      version: canary
  template:
    metadata:
      labels:
        app: myapp
        version: canary
    spec:
      containers:
      - name: myapp
        image: myapp:v2

Assuming the stable deployment has 8 replicas with label version: stable and the Service routes traffic evenly by label.

medium

A. 20%

B. 25%

C. 80%

D. 50%

Solution

1. Step 1: Calculate total replicas

   Stable has 8 replicas, canary has 2 replicas, total = 8 + 2 = 10 replicas.

2. Step 2: Calculate canary traffic percentage

   Traffic is split evenly by label, so canary gets 50% traffic regardless of pod count.

3. Final Answer:

   50% -> Option D

4. Quick Check:

   Service splits traffic evenly by label = 50% canary [OK]

Hint: Check how Service splits traffic: by pods or labels [OK]

Common Mistakes:

• Assuming traffic splits by pod count instead of labels
• Ignoring label-based routing in Service
• Miscounting total replicas

4. You applied a canary Deployment but users report they see only the old version. What is the most likely cause?

medium

A. The image tag in the canary Deployment is incorrect

B. The Deployment replicas are set to zero

C. The Service selector does not include the canary label

D. The pod resource limits are too high

Solution

1. Step 1: Understand how Service routes traffic

   Service routes traffic to pods matching its selector labels.

2. Step 2: Identify why canary pods get no traffic

   If Service selector misses canary label, canary pods won't receive traffic, so users see only old version.

3. Final Answer:

   The Service selector does not include the canary label -> Option C

4. Quick Check:

   Service selector missing canary label = no canary traffic [OK]

Hint: Check Service selector matches canary pod labels [OK]

Common Mistakes:

• Assuming zero replicas without checking
• Blaming image tag without logs
• Ignoring Service selector labels

5. You want to roll out a canary deployment with 10% traffic to the new version and 90% to stable. You have 10 stable pods and 2 canary pods. How should you configure the Service to achieve this traffic split?

hard

A. Set Service selector to include both stable and canary labels and use weighted routing with 10% weight on canary

B. Create two Services, one for stable and one for canary, and use an Ingress with traffic splitting

C. Use a single Deployment with 12 replicas and update image tag gradually

D. Set Service selector to only stable label and manually scale canary pods to 1

Solution

1. Step 1: Understand traffic splitting in Kubernetes Service

   Standard Kubernetes Service does not support weighted traffic splitting by itself.

2. Step 2: Identify method to split traffic by percentage

   Using two Services and an Ingress or service mesh allows weighted traffic splitting (e.g., 10% to canary, 90% to stable).

3. Step 3: Evaluate options

   Create two Services, one for stable and one for canary, and use an Ingress with traffic splitting describes creating two Services and using Ingress for traffic splitting, which is the correct approach.

4. Final Answer:

   Create two Services, one for stable and one for canary, and use an Ingress with traffic splitting -> Option B

5. Quick Check:

   Weighted traffic split requires Ingress or service mesh [OK]

Hint: Use Ingress or service mesh for weighted traffic split [OK]

Common Mistakes:

• Expecting Service selector to do weighted routing
• Scaling pods to control traffic percentage
• Using single Deployment for canary traffic split