In general you do it by doing a failover behind some variation of a reverse proxy.
If you can start new instances quickly and clients can handle short delays you can do it by just stopping the old deployment and starting the new one, booting off of the snapshotted state from the prior deployment.
If you need “instant” you do it by implementing some form of catchup and then fail over.
It is a lot easier to do this if you have a dedicated component that ”does” the failover, rather than having the old and new deployments try to solve it bilaterally. Could just be a script ran by a human, or something like a k8s operator if you do this a lot
If you can start new instances quickly and clients can handle short delays you can do it by just stopping the old deployment and starting the new one, booting off of the snapshotted state from the prior deployment.
If you need “instant” you do it by implementing some form of catchup and then fail over.
It is a lot easier to do this if you have a dedicated component that ”does” the failover, rather than having the old and new deployments try to solve it bilaterally. Could just be a script ran by a human, or something like a k8s operator if you do this a lot