There might be a throughput degradation in the more recent versions of stunnel. I have recently been testing the 5.32 version of stunnel and have noticed that the tps drop quite significantly when moving from 5.06 to 5.32. Im willing to admit it could be something to do with my config or testing. But if anyone could offer some suggestions it would be much appreciated. The config is setup as follows - Stunnel VIP -> Haproxy. (I have configured haproxy to return a simple page). I am using a self signed 1024 bit certificate and the cipher I am using is ECDHE-RSA-AES256-GCM-SHA384 (I also tested with aNull:eNULL:MD5:LOW:HIGH and noticed a similar drop in performance) My Stunnel config is - setuid = stunnel pid = /var/run/stunnel/stunnel.pid debug = local1.0 socket = a:IP_FREEBIND=yes socket = l:TCP_NODELAY=1 socket = r:TCP_NODELAY=1 [VIP_Name-1] cert = /root/server1024.pem ciphers = ECDHE-RSA-AES256-GCM-SHA384 accept = 192.168.80.131:443 connect = 127.0.0.1:80 connect = 127.0.0.2:80 delay = no options = CIPHER_SERVER_PREFERENCE options = DONT_INSERT_EMPTY_FRAGMENTS renegotiation = no TIMEOUTclose = 0 My HAProxy config is - global daemon stats socket /var/run/haproxy.stat mode 600 level admin pidfile /var/run/haproxy.pid maxconn 100000 tune.maxrewrite 1024 nbproc 3 defaults #mode http #balance roundrobin timeout connect 4000 timeout client 42000 timeout server 43000 peers loadbalancer_replication peer lbmaster localhost:7778 peer lbslave localhost:7778 listen VIP_Name bind 127.0.0.1:80 transparent #bind 192.168.80.121:80 transparent monitor-uri / mode http errorfile 200 /etc/haproxy/200.http listen VIP_Name_2 monitor-uri / mode http bind 127.0.0.2:80 transparent errorfile 200 /etc/haproxy/200.http All the versions of stunnel mentioned here have been built against Openssl1.0.1s I am using siege to generate the load and issuing the following command - siege https://192.168.80.131 -t1M -c 15 -b The test is stop stunnel service, replace stunnel binary with different version, restart service, run test. The results im seeing are as follows (All results are quoted in transactions per second as reported by siege). v5.06 - 2233 v5.07 - 2229 v5.25 - 2171 v5.30 - 2092 v5.32 - 302 In my results you can see roughly a 200 tps drop from version 5.06 to v5.30 then when we get to v5.32 it drops further. To reiterate the only thing I am changing in my configuration is the stunnel binary. Everything else is remaining the same. Does anyone have any ideas what could be happening? Thankyou Mark