session management for high traffic ASP.NET website.

Question

We use SQL server for our application's session state. Since the SQL server is a single point of failure, when it has problems it can affect all our customers. To mitigate this issue, we plan to create a SQL 2012 High availability instance and move .Net session management to its own servers. The SQL 2012 High availability instance can fail over automatically or manually when there are problems with a node. We are planning to use viprion to shard session state data across these lightweight AspState instances. Instead of using viprion to shard .Net session data at the webserver level, is there an alternate application level sharding approach that we can consider? This should be a common enough problem for high traffic ASP.Net sites that use .Net session management.