Blue-green deployments in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Blue-Green Deployment Basics

What is the primary benefit of using a blue-green deployment strategy in Kubernetes?

A It provides automatic rollback on pod failure without manual intervention.

B It allows zero downtime by switching traffic between two identical environments.

C It automatically scales pods based on CPU usage.

D It reduces the number of pods running to save resources.

💡 Hint

Think about how traffic is managed during updates.

Blue-green deployment uses two identical environments (blue and green). Traffic switches from one to the other to avoid downtime during updates.

💻 Command Output

intermediate

Identifying Active Service in Blue-Green Deployment

You have two deployments named app-blue and app-green. The Kubernetes service app-service currently routes traffic to app-green. What is the output of this command?

kubectl get endpoints app-service -o jsonpath='{.subsets[*].addresses[*].targetRef.name}'

A app-green

B app-blue

C app-service

D No output (empty string)

💡 Hint

The service routes traffic to the currently active deployment pods.

The command shows pod names behind the service. Since app-service routes to app-green, the output is app-green.

❓ Configuration

advanced

Correcting Service Selector for Blue-Green Switch

You want to switch traffic from app-blue to app-green by updating the service selector. Which of the following kubectl patch commands correctly updates the service selector to point to app=green?

A kubectl patch service app-service -p '{"spec":{"ports":[{"app":"green"}]}}'

B kubectl patch service app-service -p '{"metadata":{"labels":{"app":"green"}}}'

C kubectl patch service app-service -p '{"spec":{"selector":{"app":"green"}}}'

D kubectl patch service app-service -p '{"spec":{"selector":{"app":"blue"}}}'

💡 Hint

Service selectors are under spec.selector.

To switch traffic, update the service's selector to app=green. Option C correctly patches spec.selector.

🔀 Workflow

advanced

Blue-Green Deployment Traffic Switch Steps

Arrange the steps in the correct order to perform a blue-green deployment traffic switch in Kubernetes.

A 1,3,2,4

B 1,2,3,4

C 3,1,2,4

D 2,1,3,4

💡 Hint

Think about deploying, verifying, switching traffic, then cleaning up.

First deploy new pods, verify they are healthy, then update the service selector to switch traffic, and finally remove old pods.

❓ Troubleshoot

expert

Troubleshooting Traffic Not Switching in Blue-Green Deployment

After updating the service selector to app=green, users still reach the old version app-blue. What is the most likely cause?

A The Kubernetes cluster needs to be restarted to apply changes.

B The service selector was updated but the DNS cache on clients still points to old pods.

C The service ports were changed and do not match pod ports.

D The <code>app-green</code> pods are not ready or failing readiness probes.

💡 Hint

Consider pod readiness and how Kubernetes routes traffic.

If pods are not ready, the service will not route traffic to them, so users still reach old pods.