Lync Front End Server High-Availability

Providing high-availability to Lync Front End Servers is the core of a Lync high-availability design. Front End Servers run nearly every critical service in a Lync deployment, and without access to a Front End Server, users cannot even sign in. Lync Front End Servers can be configured in the topology as pools. These pools can contain up to 20 servers, allowing for increased scale and redundancy.

Lync Server 2013 allows for load balancing Front End Server pools using two methods, DNS load balancing and hardware load balancing.

DNS Load Balancing

DNS load balancing is the primary, and preferred, method for providing high-availability to Lync Front End Server pools. DNS load balancing leverages DNS round robin functionality to provide users the IP addresses of all Front End Servers in the Front End Server Pool. DNS Load Balancing in Lync Server 2013 is a combination of DNS round robin and application level load balancing intelligence that is built in to Lync Server 2013 that is used to dynamically manage registration and conferencing load on the Front End Servers. DNS load balancing provides the simplest method of providing high-availability to Front End pools. However, even when using DNS load balancing, a hardware load balancer (HLB) is still required for providing high-availability to Lync Web Services. Configuration of DNS load balancing is covered in Chapter 11, “Dependent Services and SQL.”

Hardware Load Balancing (HLB)

Hardware load balancing has been around for some time. However, these devices were originally used to distribute web traffic to web servers. As applications have evolved, HLBs have evolved to support more advanced traffic such as SIP traffic. HLBs are used to provide high-availability to Lync Front End Server pools by providing a virtual IP (VIP) for the Lync Web Services, and directing traffic to available Front End Servers in that pool. HLBs can also be used to distribute SIP traffic across Front End Server pools. However, these configurations are often complex, and if possible it is suggested to use DNS load balancing for SIP traffic.

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