HAProxy dynamic server addresses
Assuming you're happy with trusting the IP in the header of the second request, then yes, you can do it with use-server:
backend bk_foo [...] server srv_0a_00_01_05 10.0.1.5:80 weight 100 server srv_0a_00_02_05 10.0.2.5:80 weight 100 use-server %[req.hdr(x-backend-ip),lower,map_str(/etc/haproxy/hdr2srv.map,srv_any)] if { req.hdr(x-backend-ip),lower,map_str(/etc/haproxy/hdr2srv.map) -m found }Contents of /etc/haproxy/hdr2srv.map:
#ip srv_name# hex of IP used for names in this example10.0.1.5 srv_0a_00_01_0510.0.2.5 srv_0a_00_02_05If you need to down one of the servers, you should dynamically update the map to remove it, so that the requests with the header set get redirected again.
If you have multiple backends, you can do similar with use_backend.