Introduction
Eliminating single points of failure for DirectAccess deployments is crucial to ensuring the highest levels of availability and for providing the best experience for remote users. In support of this, DirectAccess servers can be configured in load-balanced clusters to provide redundancy for maximum uptime, and for scalability when additional capacity is required.
Load Balancing DirectAccess
DirectAccess supports two options for load balancing – integrated Network Load Balancing (NLB) and external load balancers. NLB is often chosen because it is simple and easy to configure, but it brings along with it some serious drawbacks. For example, NLB is broadcast-based, with cluster heartbeat message being sent to all hosts on the subnet every second. This generates a tremendous amount of noise on the wire, reducing performance for all hosts on the subnet. Further, NLB is limited with negative scalability. That is, as more nodes are added to the cluster, broadcast traffic increases exponentially and performance gains are reduced. The maximum number of NLB nodes supported in a single DirectAccess cluster is eight, but practically speaking the useful upper limit is actually four.
Why External Load Balancer?
Using an external load balancer is preferred over NLB. An external load balancer operates at the network layer (layer 3) and does not suffer from negative scalability. Clusters with as many as 32 nodes are supported, for which the capacity of each node is fully available to support client requests. External load balancers also provide granular control of traffic distribution, enabling support for previously unsupported scenarios such as active/passive failover. An external load balancer can also reduce infrastructure requirements by serving as the Network Location Server (NLS).
DirectAccess and Kemp LoadMaster
Although the integration of an external load balancer offers clear and compelling benefits over NLB, many organizations are hesitant to implement one due to perceived high costs. The good news is that Kemp offers a completely FREE version of their popular LoadMaster load balancer. Now there’s no excuse NOT to use an external load balancer! Download and install the free Kemp LoadMaster load balancer today and begin experiencing the benefits today. Be sure to also download the Windows Server DirectAccess Integration Guide for Kemp LoadMaster here.