Dynamic Backend Selection based on Client IP in Haproxy - load-balancing

Question

I would like to choose a backend based on custom hash function that hashes the client ip (I know this is not ideal but I am trying this approach out).
A pseudo config would look like,
frontend myserver
bind *:80
acl MyHash(clientIP) %2
use_backend backend0 if {MyHash(clientIP)%2 -m int 0}
default_backend backend1
backend backend0
balance leastconn
server server-1 <ip>:port check
server server-2 <ip>:port check
backend backend1
balance leastconn
server server-3 <ip>:port check
server server-4 <ip>:port check
The reason I am doing this instead of the following alternate, is that, I don't want connect a client to a server all the time, instead distribute the load among the servers that belong to same cluster.
server-[1-2] form a cluster and so do server-[3-4].
frontend myserver
bind *:80
default_backend mybackend
backend mybackend
balance source
hash-type consistent
server server-1 <ip>:port check
server server-2 <ip>:port check
server server-3 <ip>:port check
server server-4 <ip>:port check

Answer 1

Able to figure this out.
frontend myserver
bind *:80
acl select_backend_0 src,field(-1,.),mod(2) -m int 0
acl select_backend_1 src,field(-1,.),mod(2) -m int 1
# Use section can be further optimized, like using a map or something.
use_backend backend0 if select_backend_0
use_backend backend1 if select_backend_1
backend backend0
balance leastconn
server server-1 <ip>:port check
server server-2 <ip>:port check
backend backend1
balance leastconn
server server-3 <ip>:port check
server server-4 <ip>:port check