(Self hosted Router) Federation Subscription that scales

[FuJuntao]

Lately our team was trying to deploy the self hosted Router for Federation Subscription.
I found that the doc didn't mention how to do it, more specifically, how to leverage callbacks to scale the Router.

According to my testing, only the Router instance that initiated the subscription can handle the callback.
Meaning a subscription request coming from a client, can only be processed by the same Route instance all along, even if it's using a shorted-lived multipart http request.

Then how do we scale the deployment? I assume if any router can handle any "callback" would make it much easier?

You offered the GraphOS platform, how do you scale?