This issue tracks providing runtime configuration via a pub-sub xDS API called TDS. The idea is that any runtime feature should also be configurable via xDS (and bootstrap statically).

I think a good approach to this might be to define the runtime canonically in protobuf. It would still retain its existing tree hierarchy and types, but the implementation would derive these from the protobuf definition. That way we can easily return a runtime update over TDS or place it in bootstrap.

Another alternative would be to make the TDS/boostrap interface just a key/value map, where runtime settings can be updated via application of the new settings. This would lose some of structural typing advantages of the canonical proto solution, but would be very easy to make work today.