Thanks to Let's Encrypt program, we can now generate free SSL certificate.
I used the beta program with success, but now I tried on another server running through HAProxy. This is a trick to combine certificate, chain and private key in order to be loaded by HAProxy :)
cat cert.pem chain.pem privkey.pem > combined.pem
Following is the command I used to generate the certificates, can be improved to set email address and accept conditions.
./letsencrypt-auto certonly -a webroot --webroot-path /var/www/ -d domain.net -d www.domain.net