CI/CD · Ship safely, repeatedly
How does blue-green deployment work?
Short answer
Blue-green runs two identical environments. You deploy to the idle one, verify it, then switch traffic from the old version to the new one. The old environment stays available for a fast rollback.
The switch is usually at a load balancer, DNS or service selector. Because the old environment is still running, rollback is a traffic switch back rather than a rebuild or redeploy.
- Provision or maintain two environments with the same configuration shape
- Deploy and test the new version on the idle side
- Switch traffic atomically and watch error rates and latency
- Keep the previous version warm until the verification window passes
- Tear down or reuse the old side after the rollback window
apiVersion: v1
kind: Service
metadata:
name: checkout
spec:
selector:
app: checkout
version: green
ports:
- port: 80
targetPort: 8080Follow-ups you should expect
Interviewers use these to check whether the first answer was understanding or memorisation.
- 1What does the traffic switch usually look like?
- 2How do you handle database changes in blue-green?
- 3What is the cost trade-off?
- 4How long do you keep the old environment running?
Say it in the interview
Blue-green runs two identical environments and deploys the new version to the idle one. After verification I switch traffic over and keep the old environment running as the rollback target. The main advantages are a fast switch and a clean rollback. The constraints are duplicate capacity and database compatibility, since both versions may run briefly during the cutover.
Use this as a model, not a script. Saying it in your own words is what makes it survive follow-up pressure.
Related questions
Reading is step one
Now say it out loud.
Understanding an answer and delivering it under pressure are different skills. Rehearse this topic in a live CI/CD mock interview and get scored feedback on depth, clarity and confidence.