DNS Load Balancing Requirements

If the limitations of DNS load balancing described earlier don’t pose any issues to an organization’s Lync Server deployment, the organization can proceed with that method instead of purchasing a hardware load balancer. There are actually some advantages to using DNS load balancing, mainly the simplicity involved in configuration that just involves using multiple A records for the same name in public DNS. Table 31.3 shows the DNS records required to achieve DNS load balancing.

Table 31.3. DNS Load-Balancing Entries

When using DNS load balancing, the Edge Server can use private IP addresses that are translated by NAT for all three roles, including the A/V Edge. This is a big advantage for organizations that might not have many public IP addresses available, or an existing perimeter network with publicly routable addresses.

DNS load balancing also requires three fewer IP addresses than a hardware load-balancing solution. Each Edge Server IP still needs to be mapped to a unique public IP address if it is being translated by NAT, but there is no concept of a VIP. Instead, each client has logic built-in to realize that there are multiple servers with separate IP addresses to which it could connect.

Another advantage of DNS load balancing is that the native server-draining feature in Lync Server is available. This enables administrators to prepare a server by maintenance through the Lync Server Control Panel the same way as the other roles.

In some organizations, the team responsible for Lync Server might not be the same team that manages the network and hardware load balancers, which can make it difficult to coordinate preparing a server for maintenance. Instead of the Lync Server administrators quickly draining a server’s connections, they might need to submit a request to have the network team drain the load balancer connections for a particular node and then check back later to determine whether the connections have cleared. Sometimes this separation of teams can be just as efficient as one person having complete control, but often it slows down the maintenance process.