Use caution when installing and SSL certificate for OWA or OMA on a clustered Exchange server. When you configure Microsoft Outlook Web Access to use a Secure Sockets Layer (SSL) connection to a Microsoft Exchange Server 2003 computer, you may notice a dramatic increase in CPU usage by the Lsass.exe process and by the Resrcmon.exe process. The only way to get the process back in check is to reboot the server. This problem occurs on an Exchange 2003 computer that is running in a Microsoft Windows Server 2003-based cluster. [more]
Additionally, an Error event that is similar to the following is logged in the Application log:
Event Type: Error
Event Source: MSExchangeCluster
Event Category: Services
Event ID: 1014
Date: Date
Time: Time
User: N/A
Computer: Computer Name
Description: Exchange HTTP Virtual Server Instance - (GENESIS): IsAlive checking for this resource failed due to timeout
The solution is to install Exchange 2003 SP2 or you can call MS for the hotfix. I actually like the SSL termination on the ISA server approach a little better. If the SSL tunnel is terminated on the ISA server, you can reinitiate another SSL tunnel with another internal certificate OR you can redirect the traffic to port 80 on the inside interface. Terminating the SSL connection on the ISA server offloads processing from the Exchange server, which is usually a good idea.