We have two identical SiteScope server, they are installed in the same directory and the server properties are also same. We have applied failover license on the failover sis. Both the Sitescopes have been upgraded from 11.20 to 11.23 using patch SIS_00274.
When we try to do the failover, we get an error for handshake. We tried both, port 8080 and 8888. Both give error.
What you'll see if it's listening on HTTPS is for the screen to essentially go blank. If it just hangs for a bit and comes back with an unable to connect message, your primary Sitescope is not listening on HTTPS.
In order to resolve, either untick the "Secure connection" option in your high availability settings, or enable HTTPS on your primary Sitescope. Could be that you had it on HTTPS pre-upgrade, but that it's now listening on HTTP only. Either that, or there's a problem with your SSL certificates between your primary and failover Sitescopes.
Again, I do not have much experience with SSL and Sitescope, but pretty sure there must be a section on SSL and failover in one or more of the Sitescope documents (I'll try to see if we can narrow down anything documentation wise).
EDIT: Forgot to add, in our case the port is definitely 8080 and not 8888.
EDIT #2: Looks like you'll need to go over the "Configuring SiteScope to Use SSL" section in the Sitescope deployment guide. From the looks of things, you'll need to do this on BOTH your primary and failover Sitescopes in order to use SSL on both.
It also looks like some of these SSL settings do get lost when upgrading Sitescope (at least from 11.21 to 11.22, likely the same case when upgrading from 11.20 to 11.23).