What Is Blue/Green Deployment in Kubernetes?
Blue/green deployment in Kubernetes is a release strategy where two environments (blue = current, green = new) run in parallel, and traffic is switched instantly via a Service or Ingress to enable zero-downtime deployments. [#definition]
When to Use
- Deploying high-traffic apps without downtime
- Fast rollback if new code breaks
- Upgrading infrastructure or config safely
- Testing production-like workloads before release
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.
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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
TAGS
System Design Interview
System Design Fundamentals
CONTRIBUTOR
Arslan Ahmad
ex-FAANG engineering manager and author or Grokking series.
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