Redis is a great choice for Sitecore’s shared session database. Sitecore has a good article which describes how to set this up, and links to this article to explain all options. I was running into issues when setting this up with my Azure Redis Cache which is using an access key. The “accessKey” attribute in the provider node was populated with the access key form the Azure portal. Initially i was seeing something like this in the log:

INFO  redisname.redis.cache.windows.net:6380,abortConnect=False
INFO
INFO  Connecting redisname.redis.cache.windows.net:6380/Interactive...
...
INFO  redisname.redis.cache.windows.net:6380 faulted: UnableToResolvePhysicalConnection on PING

Then the log would be full of errors like below:

ERROR GetItemFromSessionStore => StackExchange.Redis.RedisConnectionException: No connection is available to service this operation: EVAL
   at StackExchange.Redis.ConnectionMultiplexer.ExecuteSyncImpl[T](Message message, ResultProcessor`1 processor, ServerEndPoint server)
   at StackExchange.Redis.RedisBase.ExecuteSync[T](Message message, ResultProcessor`1 processor, ServerEndPoint server)
   at StackExchange.Redis.RedisDatabase.ScriptEvaluate(String script, RedisKey[] keys, RedisValue[] values, CommandFlags flags)
   at Sitecore.SessionProvider.Redis.StackExchangeClientConnection.c__DisplayClass12_0.b__0()
   at Sitecore.SessionProvider.Redis.StackExchangeClientConnection.RetryForScriptNotFound(Func`1 redisOperation)
   at Sitecore.SessionProvider.Redis.StackExchangeClientConnection.RetryLogic(Func`1 redisOperation)
   at Sitecore.SessionProvider.Redis.StackExchangeClientConnection.Eval(String script, String[] keyArgs, Object[] valueArgs)
   at Sitecore.SessionProvider.Redis.RedisConnectionWrapper.TryTakeWriteLockAndGetData(String sessionId, DateTime lockTime, Object& lockId, ISessionStateItemCollection& data, Int32& sessionTimeout)
   at Sitecore.SessionProvider.Redis.RedisSessionStateProvider.GetItemFromSessionStore(Boolean isWriteLockRequired, HttpContext context, String id, Boolean& locked, TimeSpan& lockAge, Object& lockId, SessionStateActions& actions)

The only way I was able to get this to work was by not putting the access key in the provider but instead specifying it in the connection string (in ConnectionStrings.config):

<add name="sharedSession" connectionString="redisname.redis.cache.windows.net:6380,password=rediskey,ssl=True,abortConnect=False" />

Sitecore is now able to connect to Redis and all errors are gone from the log. Below lines from log file show the successful connect:

INFO  redisname.redis.cache.windows.net:6380,password=rediskey,ssl=True,abortConnect=False
INFO  Connecting redisname.redis.cache.windows.net:6380/Interactive...
....
INFO  Connect complete: redisname.redis.cache.windows.net:6380