Voici ma solution :
%{SYSLOGTIMESTAMP:timestamp} %{DATA:Aloha_name} %{DATA:SyslogFacility} %{DATA:Haproxy_process}: %{DATA:client_ip}:%{INT:client_port} \[%{HAPROXYDATE:accept_date}\] %{NOTSPACE:frontend_name} %{NOTSPACE:backend_name}/%{NOTSPACE:server_name} %{INT:Tq}/%{INT:Tw}/%{INT:Tc}/%{INT:Tr}/%{INT:Tt} %{INT:http_status_code} %{NOTSPACE:bytes_read} - - ---- %{INT:actconn}/%{INT:feconn}/%{INT:beconn}/%{INT:srvconn}/%{NOTSPACE:retries} %{INT:srv_queue}/%{INT:backend_queue} "%{WORD:Method} %{URIPATHPARAM:request} HTTP/%{NUMBER:http_version}"
https://cdn.haproxy.com/wp-content/uploads/2017/07/aloha_load_balancer_memo_log.pdf