Server-side: handle reconnection to different server

[chris-ray]

If after a delay, or a lost network connection the websocket disconnects. It seems it will never reconnect.

[SteveSandersonMS]

Yes, this is correct. In fact there are a wide range of cases where recovery behavior is needed (e.g., server goes down and user needs to be transferred to a different server within the load balancing group).

We've been considering these scenarios in detail. However I don't think we have a tracking issue for them yet, so I'm going to change the issue title for this one and use it as the tracking issue.

[SteveSandersonMS]

Note that the expected solution for this is going to involve the app developer making their per-user state serializable so that it's transferrable between servers and doesn't have to be kept live in the server's memory forever. When a user disconnects, we don't know if that's because they are finished, or if it's because there was a network issue and they will attempt to reconnect and resume shortly. So the server doesn't know to keep their state in memory, and even if it does, that wouldn't guarantee the user reconnects to the same server.

In summary, a robust solution will involve the app developer doing some work and accounting for it in their app architecture. We intend to provide patterns to make this straightforward and robust, but it will still require the app developer to be aware of them and fit in with those patterns.

[wanton7]

Our company would use server side Blazor for some of our internal tools if there was even simple reconnect support. That would only supports single server and keeping state in memory with timeout.

[TheFanatr]

Assuming that something similar to what is detailed below has already been drafted by the Blazor team internally, this is being submitted here just it in case it helps gets any extra thoughts moving about how the structure of a session control system could work.

Essentially, I am proposing that a new API be created called Session, containing static methods for terminating, resetting, transferring, temporarily (based on a predicate and an auxiliary timeout value) extending the timeout for, or restarting a session. It should also contain a property for the current session, as well as a configuration struct for settings regarding the session's timeout and disconnection settings, providing a settable default instance as well. Session should also have instance events for disconnection, timeout, and reconnection, as well as a settable state object that could be used for identification and data serialization upon disconnection or whenever.

It could also be structured similarly to IJSInterop, with ISession and an implementation called ServerSideBlazorSession or something.

Hope I could provide something useful.