Bandit websocket server connection terminated reason={:error, :closed}

I was able to capture some additional information using Bandit / Thousand island telemetry.

It turns out the error that is causing those disconnections is:

[:thousand_island, :connection, :send_error]

with

measurements=%{error: :closed, ...}

If this is deployed somewhere, it might be your infrastructure provider not allowing long-lived connections.

Yes, that definitely makes sense!

Additionally, in my testing I noticed that some WebSocket clients don’t actually send a close frame or status code when they disconnect, they just close the underlying TCP connection. That was a bit surprising and explains why the server sees it as an abrupt disconnect rather than a regular shutdown, which in turn makes it harder to differentiate network interruptions from regular application-level connection terminations.