The ICM Web Option system is comprised of two paths--a routing path and a CTI path. This section describes only the routing path. When Trailhead routes requests to the ICM Central Controller using a routing configuration that includes the Cisco LocalDirector, the goal of the configuration is to eliminate a single point of failure, namely Trailhead.
If any of the following events occur, the system cannot route Web session requests.:
The Trailhead server goes down
The Trailhead/Media Blender connection fails.
The Routing Media Blender fails.
The connection between the Media Blender and the Web PG fails.
With the proposed solution using redundant LocalDirectors, Web session requests coming from the Web site, are routed to the redundant routing path, which is shown in the following figure:
Trailhead failover is accomplished using the Cisco LocalDirector. The LocalDirector offers a high-availability, Internet scalability solution that provides load balancing and a failover mechanism to eliminate points of failure for a server farm.
You can use a Cisco LocalDirector and the LocalDirector User Interface (LUI) software to load balance and probe two Trailhead servers. Load balancing, performed by the LocalDirector, is the distribution of traffic between the two servers. Probing, performed by the LUI, is the checking of the servers at specified intervals to be sure that the Web link is active. If the LUI probe detects that a Web link is inactive for one Trailhead server, it will direct the LD to designate that server as "out of service" (OOS) and direct traffic to the other Trailhead server.
Any ongoing sessions on the Trailhead server might be lost, but new session requests will be routed. The components or links that have gone down can be restored by hot swapping.
Note that this configuration does not eliminate or overcome all modes of failure. Some of the limitations of the system include:
Failover detection is limited to detecting if the Trailhead server is reachable over the network.
If a Cisco Collaboration Server or a Cisco Media Blender in the CTI path of the system (not shown above) goes down, the system might still direct requests to that server. Such requests will, however, not be served.