All of these products that constitute a single point of failure have an easy answer for robustness: buy two! Some provide facilities for IP takeover, where one takes the place of the other should it's peer fail. Nonetheless, it still means twice the expense.

Besides the Front End Gatekeepers, a few vendors, such as Resonate and BrightTiger, offer Distributed Software Agents that integrate with the OS directly on your hosts. This approach offers the advantage that if the primary host is down, a backup can take over that role and further backup's can be in the queue to take over as needed. When there isn't a single box to worry about, one may potentially be in for considerable cost savings providing redundancy.

Additionally, these packages can provide additional services such as content distribution and synchronization,server specific statistics and other capabilities that can only be achieved by running agents on the Web hosts themselves.

Of course, running agents on the server necessitates OS-specific compatibility. One must reckon with if and how well their OS is supported by the vendor.