I have an ASP.NET Owin Web Api which is load balanced, which means there are multiple instances of it which don´t know each other. The web api hosts a SignalR hub with an SQL Server Backplane (for synchronising between instances), so clients can exchange messages regardless of which instance of the web api they are connected to. Everything working so far.
Client session data is stored in the db. The web api needs this info for processing requests for the client. Because it would be too slow to read the session data from the db for every client request, the web api is reading it only once (on first request from the client session) and caching it in-memory. This also works across multiple instances of the web api as every instance is holding it´s own session data cache.
But now the clients should be allowed to change for example the language, which results in an updated language in the session data stored in the db. The web api instance which processes the "change-language"-request of course can react to the changed session data and clear the session from it´s cache, which will lead to a reread of the session data from the db on the next client request. But the other web api instances don´t know about the session data change, their caches now hold outdated session data.
The web api instance which processes the "change-language"-request would somehow need to notify the other instances to drop their cache for session xyz. Unfortunately the instances don´t know each other, but all instances host SignalR hubs which are synchronised through the SingalR SQL server backplane.
Unfortunately a SignalR hub cannot directly send and receive messages. A HubConnection (client) is needed to do that. So the idea is when every web api instance is connecting to it´s own SignalR hub, it would be able to send messages to itself, which are then spread out to the other instances via the SQL server backplane synchronisation. But a HubConnection can only be established with an URL (http://host:port/signalr) but the web api instance doesn´t know it´s own base url.
So finally my question is: Is there any way to establish a HubConnection to a hub running in the same process without providing an URL (I have access to the hub object)? If not, is there any way for a SignalR hub to spread out messages and listen to messages through the backplane without a client (hub-2-hub communication)? If not what else could I do to notify other instances of my load balanced web api and advice them to drop their session data cache?
Solved through distributed caching (IDistributedCache), as mentioned by Panagiotis Kanavos in the comments.