F5 to RabbitMQ

XFF is HTTP only as always. 

if you need something like this for rabbitMQ, you must route the traffic through f5 even without SNAT. 

easiest would be to put the server network for the app traffic directly to the f5. so the bigip is the gateway for the server in this traffic. 

But yeah you need to adjust your network for this. 

There are always a few apps that require non-snat solution.

the only other "solution" I'm aware of is something like this: RFC 6967 - Analysis of Potential Solutions for Revealing a Host Identifier (HOST_ID) in Shared Address Deployments (ietf.org)

NGINX is able to do so and a few days ago there was a iRule postet for this topic: Proxy Protocol v2 Initiator | DevCentral (f5.com)

Unfortunately, I never worked with such solution, it is always "easier" to add a vlan / ip network between server and f5 bigip to do inline :)