Hello! We are setting up some different implementations of mail cluster and have some question related to HAProxy. Our cluster has 3 backend nodes with normal mail services. Currently there is a private floating IP between HAProxy on 2 frontend nodes. The traffic from applications (which are on backend servers) is handled by HAProxys (on frontend nodes) through floating IP and distributed back to backend servers. This is just for applications and works very well. Public traffic is handled by public floating IP.
Now I have a question. Would it be better to put HAProxy on every backend node and change the backend service ports to different value than default. Then bind HAProxy to default service ports and proxy traffic to changed backend port. By default traffic would go to localhost, but fail-over to other 2 backend nodes.
We have this implementation for Percona cluster, 3 nodes with MySQL and HAProxy installed. MySQL default port set to 3307 and HAProxy bind to 3306. Then by default redirect to local mysql service, and backup to other 2. This is working very well for some years now.
We would do this for all mail services, moving default backend port +1 and giving default port to HAProxy.
Is far as I see, there is less roundtrip for the traffic, because we go localhost by default. If there are more app servers than private floating IP is more optimized, than putting HAProxy on every app server. But are there any other concerns with running HAProxy on backend nodes and handle traffic between nodes in case of localhost failure? Would this implementation be better then the floating private IP?
Pros and cons in your opinion would be really appreciated.
Thank you very much,