Hello,

I have been using Stunnel 3.5.44 (latest for Ubuntu 18) to connect to my remote 
load balancer which serves traffic to several backend nodes. 

After recent O/S update, I have noticed one weird issue. I am seeing frequent 
TIMEOUTconnect and TIMEOUTclosed exceeded errors when stunnel service tries to 
connect to backend nodes via load balancer in round robin mode.

If I replace load balancer or multiple backends (to rule out DNS issue) entries:

connect = remote-load-balancer:8080
Or
connect = remote-backend-node1:8080
connect = remote-backend-node2:8080

With single backend entry like this:

connect = remote-backend-node1:8080
Or,
connect = remote-backend-node2:8080

Then those errors go away.

I have tested on multiple servers with different backends and timeout 
configuration and all are showing same issues so the problem seems like not 
related to specific server of backend.

Any idea what could cause this issue?

Thanks in advance,
Ferdous 

Reference:
https://launchpad.net/ubuntu/bionic/+package/stunnel4

Stunnel sample config:

pid = /var/run/stunnel4/stunnel.pid
output = /var/log/stunnel4/stunnel.log

socket = l:SO_KEEPALIVE=1
socket = r:SO_KEEPALIVE=1
socket = r:TCP_KEEPIDLE=120
socket = r:TCP_KEEPINTVL=30
socket = r:TCP_KEEPCNT=6
socket = l:TCP_KEEPIDLE=120
socket = l:TCP_KEEPINTVL=30
socket = l:TCP_KEEPCNT=6

[remote]
client = yes
accept = 127.0.0.1:6500
connect = remote-load-balancer:8080
cert =  /opt/service/etc/cert.d/remote.crt
key = /opt/service/etc/key.d/remote.key
sslVersion = TLSv1.2
debug = info
verifyChain = no
verifyPeer = no
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