Use static dictionary in asp.net web application

Question

I use SignalR in my asp.net web application. Session state doesn't exist in SignalR hub, so I decided to save username <-> connectionId pair in static dictionary.

public static class UsernameConnectionsMaps
{
    private static Dictionary<string, string> data = new Dictionary<string, string>();

    public static void Add(string username, string connectionId)
    {
       data[username] = connectionId;
    } 

    public static string Get(string username)
    {
       return data[username];
    }

    public static void Remove(string username)
    {
       return data.Remove(username);
    }  
}

On a particular controller request, I want to send data to the client with signalR. Knowing the username of current user, I can easily get connectionId for the client and send data.

I use Get method in my controller. I use Add and Remove methods in hub's OnConnected() and OnDisconnected() methods respectively.

I am interested in, if this solution will have any problem regarding thread safety (or other) in my web application? What will be better approach?

Answer 1

If you use a static dictionary you will lose the ability to scale out your API. Each instance will keep a different static Dictionary, so notifications will not always reach their destination, consider azure signalr or some kind of persistent storage like redis.

Answer 2

The best you can do and it is what is said in the Microsoft documentation, map users to groups, even if it will produce groups with single users or a groups with many users that are actually the same user. Even if you will use Redis backplane or Azure SignalR , you will have the groups in all context and can communicate with them, add, remove and etc...

A single user can have multiple connections to a SignalR app. For example, a user could be connected on their desktop as well as their phone. Each device has a separate SignalR connection, but they're all associated with the same user. If a message is sent to the user, all of the connections associated with that user receive the message.