server affinity for dependency services

we have one server farm which has multiple servers. On each server, we have 2 services running. Each service on a different secondary IP address. End user always reaches the first service then second. We have set up 2 vIP for these 2 services on F5 LTM. from f5 point of view, we have 2 vIP and 2 pools.

We want to keep server affinity, which means:

if user reach server 1 for service 1 and we want the user to use the same server for service 2 if server 1 is up.

Anybody can help? Any idea is highly appreciated.