The Front End server is the core server role, and runs many basic Lync Server functions. The Front End servers, along with the Back End Servers that provide the database, are the only server roles required to be in any Lync Server Enterprise Edition deployment.

Front End server includes the following functionality:

  • User authentication and registration
  • Presence information and contact card exchange
  • Address book services and distribution list expansion
  • IM functionality, including multiparty IM conferences
  • Web conferencing and application sharing (if deployed)
  • Application hosting services, for both applications included with Lync Server (for example, Conferencing Attendant and Response Group application) and third-party applications
  • Application services for application hosting and hosts applications (for example, Response Group application, and several others)

Additionally, one Front End pool in the deployment also runs the Central Management Server, which manages and deploys basic configuration data to all servers running Lync Server 2010. The Central Management Server also provides the Lync Server Management Shell and file transfer capabilities.

The Back End Servers are database servers running Microsoft SQL Server that provide the database services for the Front End pool. Back End Servers do not run any Lync Server software. If a SQL Server cluster is already deployed for other applications, this cluster can be used for Lync Server 2010, if performance allows.

Information stored in the Back End Server databases includes presence information, users' Contacts lists, conferencing data including persistent data about the state of all current conferences, and conference scheduling data.

Front End Server Scalability

A Front End pool, if deployed on physical hardware, should have one Front End server for every 10,000 users homed in the pool, plus an additional Front End server to provide good performance when one server is unavailable. The maximum number of users in one Front End pool is 80,000. If the number of users exceeds 80,000 users at a site, additional Front End pools can be deployed. To provide High Availability at least two Front End servers are required.

The additional Front End server ensures good performance in case one server is unavailable. When an active server is unavailable, its connections are transferred automatically to the other servers in the pool.