global
maxconn 2048
ssl-default-bind-options ssl-min-ver TLSv1.2
ssl-default-bind-ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AE>
tune.ssl.default-dh-param 2048
user haproxy
group haproxy
daemon
log /dev/log    local0
log /dev/log    local1 notice
chroot /var/lib/haproxy
ssl-server-verify none


defaults
log     global
mode http
option  httplog
option  dontlognull
option forwardfor
maxconn 2000
timeout connect 5000
timeout client 50000
timeout server 50000
errorfile 400 /etc/haproxy/errors/400.http
errorfile 403 /etc/haproxy/errors/403.http
errorfile 408 /etc/haproxy/errors/408.http
errorfile 500 /etc/haproxy/errors/500.http
errorfile 502 /etc/haproxy/errors/502.http
errorfile 503 /etc/haproxy/errors/503.http
errorfile 504 /etc/haproxy/errors/504.http


frontend http_fe
bind *:80
bind *:443 ssl crt /etc/letsencrypt/live/monsite/monsite.fr.pem
http-request redirect scheme https unless { ssl_fc }
http-response set-header Content-Security-Policy upgrade-insecure-requests
acl acl_a hdr(host) a.monsite.fr
acl acl_b hdr(host) b.monsite.fr
use_backend backend_a if acl_a
use_backend backend_b if acl_b


backend backend_a
cookie cookie_monsite.fr insert nocache
server a.monsite.fr 10.10.10.1:80 check cookie stcookie01 


backend backend_b
cookie cookie_monsite.fr insert nocache
server b.monsite.fr 10.10.10.2:80 check cookie stcookie02 

When you make a certificate request via certbot, you can declare multiple subdomains for the same certificate.

Once your certificate is generated, you will need to merge the certificate and the key.

cd /etc/letsencrypt/live/monsite/
cat fullchain.pem privkey.pem > monsite.fr.pem