Chris May

With Windows Servers, you can setup a cluster using built in Network Load Balancing.

The interesting thing about doing load balancing via software, is that once you get up around 4-5 servers, you stop gaining in performance when you add new machines, because of the added overhead associated with mainting N number of new relationships between the servers.

Also, if you use NLB and you set them up to not use any type of server affinity (i.e. a users request might hit any of the servers at any time) you will pay a serious penality if you are using SSL because each new request to a new server will require a new negoation of the SSL credentials.

We had a problem last night as we attempted to update our site certificate on our NLB website.

We have 2 machines in the cluster, and after updating the certificate on both of them, the site stopped responding over https.

We spent a LOT of time trying to figure out what was wrong with our new certificate, or the way we had set it up.

In the end, it turned out that that when we updated the certificate, it AUTOMATICALLY removed the NLB IP address from the IPs that are listening for port 443. 

So the result was that each server would respond over SSL on it's own, but when you tried to access the cluster by it's IP address over SSL, there would be no response.

It was really easy to fix, but a real pain to find.