Achieving high availability for Client Access servers is a two-step process. First, you need to deploy multiple CASs, and second, you need to use a load balancing solution that best meets your organization's needs and requirements. This will significantly decrease, or even fully prevent, downtime and avoid single point of failures for this role.

With all the architectural changes made to Exchange 2013, Layer 4 load balancing is now a viable solution, and one that is more than adequate for most organizations. However, for some specific scenarios, Layer 7 might still be required due to its capabilities such as to analyze traffic as it passes through the load balancer.

Finally, it is crucial that certificates and Exchange services such as Autodiscover are correctly configured to take full advantage of the load balancer capabilities and Exchange availability features.

In the next chapter, we will explore high availability for the Mailbox server role, including all the changes and improvements...