Zero-downtime deployment for a Spring Boot application is commonly achieved with a blue-green deployment strategy, which keeps two identical production environments and switches traffic between them.
Key Points: • The "blue" environment serves live traffic while the new version is deployed to the idle "green" environment. • The green environment is smoke-tested with health checks before any real traffic is routed to it. • Traffic is switched from blue to green at the load balancer or router level, with essentially no gap in availability. • If something goes wrong post-switch, traffic is routed straight back to blue, giving a fast, low-risk rollback. • Rolling deployments (replacing instances gradually behind a load balancer) and canary releases are related alternatives that achieve a similar zero-downtime goal.
Example: An e-commerce checkout flow stays fully available during a release because the new version is deployed and verified on the green environment first, and the switch-over happens instantly at the router, with blue kept warm as an immediate rollback target.
Interview Tip: A concise interview answer is:
"I'd use blue-green deployment: deploy the new version to an idle environment, run health checks and smoke tests against it, then switch traffic over at the load balancer once it's verified. Keeping the old environment live but idle gives an instant rollback path if anything goes wrong."