Why there is downtime while rolling update a deployment or even scaling down a replicaset
To deploy an application which will really update with zero downtime the application should meet some requirements. To mention few of them:
- application should handle graceful shutdown
- application should implement readiness and liveness probes correctly
For example if shutdown signal is recived, then it should not respond with 200 to new readiness probes, but it still respond with 200 for liveness untill all old requests are processed.