Envoy currently hard codes h/1.1 for http health checking: https://github.com/envoyproxy/envoy/blob/master/source/common/upstream/health_checker_impl.cc#L211.

Would be nice to be able to configure this, either explicitly in the hc config or by having it respect the http2_protocol_options on the cluster that's being health checked. Having it respect the cluster setting seems the most natural to me, though I'm not sure if we're concerned about changing behavior here.