Forwarding request to all pool members

From your diagram want you need is to clone server side traffic.

I think you have 4 options:

1. Within an iRule you can use iRules clone to do this to a pool, pool member or in v13 you can also clone to a VLAN but no idea how this works. However, you can only clone to a single destination so if you have a pool of two servers you can see which one is selected during LB select event (or by persistence) then clone to the other server. But this will not scale.

2. iRule using SIDEBAND which are great but can be difficult to write and very difficult to get working (from what I have been told).

3. Look at an iRule with iRules-LX, this would be to write a simple iRule to pass the request and list of pool member IPs to a Node.js method which would send the POST request to each IP. Sounds like a lot of work but it will probably take less time than the SIDEBAND connection. Down side is you need to enable iRules-LX on your F5 devices and write iRule and js code to work together.

4. Look at an alternative solution, may be L3 multicast solution but not sure how you would go about doing multicast just on the server side.

Option 3 is my preferred solution but that is only because I already utilizing iRules-LX and you can make passive calls from an iRule to an iRules-LX method using ILX::notify (send data one-way to method, so is a passive call and very quick)

Finally, it might be worth asking your DEVs their solution to this if they didn't have the F5 in the way, that might trigger some alternative solution ideas.