What Is Blue/Green Deployment in Kubernetes?

Example

Run web-blue:v1 and web-green:v2. Update the Service selector from app=web-blue to app=web-green. If stable, retire blue.

Pro tip for learners:

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Why Is It Important

• Ensures zero downtime
• Decouples deployment from release
• Provides instant rollback for safer delivery

Interview Tips

• Define blue/green clearly
• Contrast with canary or rolling updates
• Mention Kubernetes objects (Deployment, Service, labels/selectors)
• Explain rollback steps and database handling

Trade-offs

• Pros: predictable cutover, rollback safety, live testing
• Cons: double infra cost, state sync complexity, added automation needs

Pitfalls

• Treating stateful apps as stateless
• Forgetting readiness/liveness checks
• Partial cutovers (Jobs/CronJobs still on blue)
• Confusing blue/green with canary