Support of DNS Load Balancer
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Concept:

I worked with a customer last year to help them deploy OCS 2007 R2. Due to business criticality of OCS setup, they wanted to go for enterprise edition with two Front End servers. But they couldn't and they settled with two SEs.
This was not the only time when a customer wanted to go for enterprise edition of OCS and they couldn’t in absence of DNS load balancing support.
I received so many queries regarding DNS load balancing support during my stint as a support engineer in Microsoft.
Every time my answer was "no, we don't support DNS load balancing with OCS".
But now Microsoft has very good news for those customers. As per Microsoft, DNS load balancing is pretty much supported for Microsoft Lync deployment.
Note: Previous versions are still not supported for DNS load balancing.
It's a great relief for the companies as they don’t need to buy HLB solution for many Lync services.
The goal behind DNS load balancing solution is to reduce dependency on HLB.
DNS Load Balancing solution is supported for following activities...

Also, Draining of applications (CAA, RGS, and Mediation Server etc.) requires DNS LB.
After discussing all good things about DNS LB, let's see what it can't do.
DNS LB can't get rid of HLB completely. HLB is still required for client to server HTTP and HTTPs connectivity. It includes address book download, meeting content download etc.

Design:

DNS A record resolves to multiple FE IPs.
If connect to an IP fails, tries to connect next one.

By

Ram K Ojha (1^st Oct 2010)