Hi Michal,

Thank you for the answer.

I found a solution for this using local port forwarding. What I do now is that I monitor my individual tunnels to check if they are alive. When one is dead I just have to change the port forward to the next stunnel entry.

I use netcat to check the connection availability as follow:

nc -z -x 127.0.0.1:$STUNNEL_PORT1 -X connect $DISTANT_SERVER $PORT

Under OS X, since 10.10 port forwarding is managed with the pfctl utility (on other linux distro we can use iptables):

echo "rdr pass inet proto tcp from 127.0.0.1 to 127.0.0.1 port $FAILOVER_PORT -> 127.0.0.1 port $STUNNEL_PORT1" | pfctl -ef - >/dev/null 2>&1

In case $STUNNEL_PORT1 is down or doesn't provide Internet access, I just switch to $STUNNEL_PORT2 and push the port forwarding rule with that port entry.

I wrote a daemon that monitors all my stunnel ports and check if they have Internet access, my PAC RETURN rules remain the same (they use my $FAILOVER_PORT), I just shifted stunnel ports to another location and use port forwarding to reach the stunnel entries that are alive.

It's working great so far.

Cheers,

Thireus ([email protected]), 
IT Security Engineer Consultant.
http://blog.thireus.com

Le 15 nov. 2015 à 19:58, Michal Trojnara <[email protected]> a écrit :

Signé partie PGP
On 15.11.2015 11:58, Thireus wrote:
> 1. I would like to know if there is a way to use failover with two
> servers with two different set of TLS cert/key.

No.  Both client and server certificates are currently set way before
stunnel connects the target.

I guess what you really need is client certificate selection based on
the list of acceptable issuers sent by the stunnel server, because
each of your stunnel servers expects client certificates issued by a
separate CA.  Am I right?

Client certificate autoselection currently works on Windows with the
CAPI engine.  I have also added a new TODO item to implement client
certificate autoselection for certificates/keys stored in PEM files:
https://www.stunnel.org/sdf_todo.html

Alternatively, you may reconfigure your stunnel servers to accept
client certificates issued by the same CA.

> 2. On the same topic, I would like to know if there is an option
> that could open the local port (accept) only when the connection
> (connect) is established?

No.

> The problem I'm facing is that I use a PAC profile with failover on
> several stunnel entries: "return PROXY 127.0.0.1:4441; PROXY
> 127.0.0.1:4442; PROXY 127.0.0.1:4443;".

Did you mean:
return "PROXY 127.0.0.1:4441; PROXY 127.0.0.1:4442; PROXY 127.0.0.1:4443
";
?

You are trying establish end-to-end failover across two (in fact
three, including connection between the stunnel server and the HTTP
proxy) separate TCP connections.  It is not possible without a
heartbeat service.

> 3. Is there another way to tweak stunnel behavior when a remote
> server is down?

You could write a heartbeat service to periodically initiate short
connections to the remote services, and then reconfigure stunnel
accordingly.  Still, this is a crude workaround and not the proper
solution.

Best regards,
Mike

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