What mechanisms are available for sharing session state in ASP.NET applications?

So we're scaling out our application to have two Web servers, and will most likely need four or five in the next year or so if all goes well.

I'm aware of sharing session state between servers with SQL Server and the ASP.NET state server. However, I'm a little concerned 开发者_运维技巧about the single-point-of-failure with the ASP.NET state server, and as we don't use SQL Server for anything else I'd rather avoid that provider, too.

What are my alternatives? What custom state servers are out there that are light-weight, can support fail-over between multiple machines, and don't require the licensing overhead of SQL Server?

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Take a look at either:

Memcached: http://memcachedproviders.codeplex.com/

or,

AppFabric: http://msdn.microsoft.com/en-us/library/ee790859.aspx

Both are free.

There's also scale out state server, but you have to pay for it: http://www.scaleoutsoftware.com/products/scaleout-sessionserver/