In previous versions of Exchange, Information Store managed the
databases and client access protocols such as Internet Message
Access Protocol version 4 (IMAP4), Post Office Protocol version 3
(POP3), Network News Transfer Protocol (NNTP), and MAPI. In
Exchange 2000, the Internet access protocols have been removed from
Information Store and are managed by IIS instead. Deploying a
front-end/back-end architecture makes it possible to manage the
Internet access protocols on a server that is separate from the one
on which Information Store and the databases run. Essentially, a
bank of protocol servers (front-end servers) handle incoming client
connections while Information Store servers (back-end servers) are
dedicated to running the databases.
Benefits of Front-End/Back-End Architecture
The main benefits of a front-end/back-end architecture are a
unified namespace and reduced overhead for Secure Sockets Layer
Unified Namespace. A unified namespace makes
administering multiple HTTP servers easier; for example, if you
have three computers running an HTTP virtual server (HTTPServer1,
HTTPServer2, HTTPServer3), normally you divide the user load by
configuring certain users to connect to HTTPServer1, others to
HTTPServer2, and the rest to HTTPServer3. If all HTTP servers are
part of a front-end/back-end architecture, user can access all HTTP
servers in your configuration with a single name. You can configure
clients to connect using the name HTTPServer, and you can use
software or hardware load balancing to randomly distribute the load
among the three HTTP servers. Also, if you want to move users'
mailboxes from one server to another, clients do not have to
reconfigure the name of the server they log on to. As your user
population grows, you can add another computer to the front-end
architecture without reconfiguring the clients.
Reduced overhead for SSL. When connections are made
using SSL, information is encrypted and decrypted, which is
processor intensive and can negatively affect performance. If your
HTTP virtual servers are deployed in a front-end/back-end
configuration, the front-end server can process the encryption with
the client. When the front-end server and back-end server
communicate, they do so without the overhead of SSL encryption.
This reduces the load on the back-end server.