Availability is the concern for any enterprise application. In Lync 2013 Microsoft took a step ahead and delivered better availability options. Lync 2013 is a next level enterprise communication and voice based solution which based on different Lync Server roles. In Lync 2013 Microsoft did a tremendous job to consolidate many Lync roles and reduced the number of Lync roles and their complexity. To know more about Lync roles click here
Lync Server Standard Edition and HA*
This is big question for all to know about HA option in Lync Server 2013 Standard Edition. Lync Server 2013 supports up to 5000 users and can be deployed in a single box but to achieve more availability (*not exactly High Availability) you can deploy Lync 2013 SE in paired pool. Paired pools means deploy two Lync SE Server and paired them in a pool. Failover In a paired pool is manual activity (can be automated by PowerShell scripting) and users will get limited functionality at the time of failover. HA can’t be achieved for Persistent Chat in Standard Edition.
Lync Server Enterprise Edition and HA
Lync Server Front End (Audio/Video, Archiving & Monitoring is collocated): High availability can be achieved by deploying Lync 2013 Enterprise Edition Server pool. In one Lync Server 2013 EE pool you can accommodate 80,000 users by deploying maximum of 12 servers. Lync 2013 Enterprise Edition is designed by using brick model which works on Windows Fabric to provide HA. In Lync 2013 EE need minimum three FE servers (MS recommendation) for one pool. For availability, Lync Server pool needs N/2, N/2+1 server in a pool to work.
Microsoft recommends if you have large conferences for more than 250 users, a separate A/V (FE) pool can be deployed.
Lync Server Back End: Lync Server uses SQL server for its backend databases. You need databases for Lync Server backend, archiving/monitoring and persistent chat which can be collocated in one SQL server or deployed on separate (MS recommended) SQL Server instances. Lync Server 2013 supports SQL mirror for its databases. It does not support SQL failover clustering (not recommended) or SQL always on feature. To configure automatic failover in SQL server mirror, you need SQL witness server which can be SQL Express edition or SQL Server instance.
Lync Mediation Server: In Lync 2013, Mediation server role can be collocated with FE server role or can be deployed separately as a pool.
Lync Persistent Chat: In Lync 2013, Persistent Chat is a new server role which replace Lync server 2010 Group Chat server component which was not part of the Lync 2010 server roles. You can deploy Lync Server Persistent Chat as a pool to achieve HA and can have maximum 8 servers in a pool (4 active and 4 passive) for 80,000 concurrent users and total 1, 50,000 users.
Lync Edge Server: Lync Edge server role can be deployed as a pool in a perimeter network to provide HA for external (outside your organization firewall) users.
Director: In Lync 2013, Director is an optional role and can be deployed in the same way as Lync Server 2010 Director pool.
Reverse proxy: Reverse Proxy is not part of any Lync Server role but required for external users. You can use Microsoft Reverse proxy solutions such TMG 2010 / UAG 2010 / IIS ARR or can have any third party solution.