Rancher lb genrerate a rule ,in the haproxy.cfg how comes the number behind the server

when i set a rule in rancher LB , in the haproxy.cfg we can see it generate the rule:
acl 80_domain_host hdr(host) -i domain
acl 80_domian_host hdr(host) -i domain:80
acl 80_domian_path path_beg -i /test
use_backend 80_domian_test if 80_domian_host 80_domian_path
backend 80_domain_test
acl forwarded_proto hdr_cnt(X-Forwarded-Proto) eq 0
acl forwarded_port hdr_cnt(X-Forwarded-Port) eq 0
http-request add-header X-Forwarded-Port %[dst_port] if forwarded_port
http-request add-header X-Forwarded-Proto https if { ssl_fc } forwarded_proto
mode http
server 2f3cb1f7106f00dad73a2530a6c25bf0c1a7bbdb IP:80

what is the “2f3cb1f7106f00dad73a2530a6c25bf0c1a7bbdb” mean ,how it comes, is there some doc.thank you