SignalR Backplane with Redis
Keeping real-time updates in sync across a horizontally scaled application, so a message reaches the people it is meant for no matter which instance they landed on.
The problem
The app runs behind a load balancer across multiple server instances, and a SignalR connection is sticky to whichever instance the client first reached. Without a shared backplane an instance only broadcasts to its own local connections, so real-time updates silently failed to reach some users depending on routing - and most visibly during deploys and autoscaling events, when connections move.
What was built
Wired up the SignalR Redis backplane so every instance publishes and subscribes through a shared Redis channel instead of broadcasting only to the connections it happens to hold.
What I'd do differently
I would have built observability into backplane message volume from the start rather than adding it after the fact.