Why does DistributedCache SessionHandler throw connection issues? - asp.net-core

Question

I have a .net core app running in VM's in azure where I use Redis as an implementation for DistributedCache. This way we have user sessions stored in Redis and can be shared in the web farm. We only use Redis for storing sessions. We are using Azure Cache for Redis with a normal instance. Both the VM and Redis are in the same region.
Add in startup:
services.AddStackExchangeRedisCache(options => {
options.Configuration = configuration["RedisCache:ConnectionString"];
});
In the web app we are having intermittent problems with redis closing connections. All calls to Redis are managed by calling session Async-methods like below.
public static async Task<T> Get<T>(this ISession session, string key) {
if (!session.IsAvailable)
await session.LoadAsync();
var value = session.GetString(key);
return value == null ? default(T) : JsonConvert.DeserializeObject<T>(value);
}
The errors we are seeing are:
StackExchange.Redis.RedisConnectionException: No connection is available to service this operation: EVAL; An existing connection was forcibly closed by the remote host.; IOCP: (Busy=0,Free=1000,Min=2,Max=1000), WORKER: (Busy=3,Free=32764,Min=512,Max=32767), Local-CPU: n/a
---> StackExchange.Redis.RedisConnectionException: SocketFailure on myredis.redis.cache.windows.net:6380/Interactive, Idle/Faulted, last: EVAL, origin: ReadFromPipe, outstanding: 1, last-read: 34s ago, last-write: 0s ago, keep-alive: 60s, state: ConnectedEstablished, mgr: 9 of 10 available, in: 0, last-heartbeat: 0s ago, last-mbeat: 0s ago, global: 0s ago, v: 2.0.593.37019
---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host..
And
StackExchange.Redis.RedisConnectionException: SocketFailure on myredis.redis.cache.windows.net:6380/Interactive, Idle/Faulted, last: EXPIRE, origin: ReadFromPipe, outstanding: 1, last-read: 0s ago, last-write: 0s ago, keep-alive: 60s, state: ConnectedEstablished, mgr: 9 of 10 available, in: 0, last-heartbeat: 0s ago, last-mbeat: 0s ago, global: 0s ago, v: 2.0.593.37019
---> System.IO.IOException: Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host..
We are not experiencing traffic spikes during the timeouts and the Redis instance is not under any heavy load.
I have no idea how to troubleshoot this further. Any idea?

Answer 1

The connection might be closed by Redis server because of idling for too long.
In your Azure Cache control you can find the config for Redis server, see if you can find timeout setting.
If you can issue commands through command line, you can also issue this command
CONFIG get timeout
If it's zero, it means no timeout.
Then the issue is with your redis client. I'm not familiar with .Net, whatever client you're using to connect to Redis server, check the timeout option or Google search (Name of the client)+ timeout and see if you can find any useful information.