SignalR - Switch between different Redis backplanes
We don't use SignalR specifically, but we have something pretty similar in the way we use redis, especially when switching between nodes. Specifically, we use redis pub/sub to subscribe to a channel, and we broadcast to that channel when changing master.
Our configuration is a little different, because we use the delimited configuration version based around ConnectionUtils.Connect(...). This means we can specify multiple nodes, with ConnectionUtils handling the concerns of figuring out which is the current master. But in your case you could perhaps publish the new master information as part of the pub/sub. I should also note that much of the code to handle switching masters (with notification) is wrapped up behind ConnectionUtils.SwitchMaster. This includes a broadcast of the change, which you can subscribe to via ConnectionUtils.SubscribeToMasterSwitch. As a minor implementation detail, the channel it uses for this is "__Booksleeve_MasterChanged" - but that is opaque if you just use the public methods.