Persistence and loadbalancing

Then, if you need persistence to the app tier, source IP persistence (doesn't matter whether SNAT enabled or not) on the inside VIP will also work (but is not going to necessarily give you even load across the app tier).

How is using SNAT on the outside F5 going to give you any sort of reasonable persistence on the inside F5 if all requests are coming from the same IP address? Without SNAT, the client's true source should be available to the inside F5 for real persistence, arguably not perfect though.

If source address is not a stable value, and you can't do something like universal persistence (something in the payload), then really the only viable approach is cookies. You must not, however, use the default BIGipServer cookie on the internal F5 as that contains the encoded value of selected pool and node on one F5, and would not necessarily work for the other. Create a cookie persistence profile on the internal F5 that does not use the default BIGipServer name. Use regular (default) cookie persistence on the external F5. You should see both cookies at the client after the first response, and you should see the internal cookie reach the internal F5 and persist accordingly.