C# - Amazon EC2 Multiple Servers Share Session State

I have a bunch of EC2 servers that are load balanced. Some of the servers are not sharing session, and users keep getting logged in and out. How can I make all the server share the one session, possibly even using a partitionresolver solution

public class PartitionResolver : System.Web.IPartitionResolver
{
private String[] partitions;
public void Initialize()
{
// create the partition connection string table
// web1, web2
partitions = new String[] { "192.168.1.1" };
}

public String ResolvePartition(Object key)
{
String oHost = System.Web.HttpContext.Current.Request.Url.Host.ToLower().Trim();
if (oHost.StartsWith("10.0.0") || oHost.Equals("localhost"))
return "tcpip=127.0.0.1:42424";
String sid = (String)key;
// hash the incoming session ID into
// one of the available partitions
Int32 partitionID = Math.Abs(sid.GetHashCode()) % partitions.Length;
return ("tcpip=" + partitions[partitionID] + ":42424");
}
}