If you have a single node elasticsearch instance and indices with replicas enabled your cluster state will be yellow. If...

If one etcd node is no longer a member of the remaining etcd cluster or fails to connect you need...

redis.io

Hint You're not able to control which redis replica will chosen for the failover. Connect to your sentinel instance...

If you want to perform a failover on another haproxy backend server this is the way you should do it...