The http healthcheck will allow a path but not a port, which is problematic for existing Dropwizard-based services which by default to have the healthcheck endpoint on a separate admin port. There are also instances of proxies where a tcp check is being done to check the health of the proxy but the traffic is going over different ports.

Envoy would need a healthcheck_port in the static configuration and the SDS API to support being a drop-in replacement for HAProxy under these conditions.

http://www.dropwizard.io/1.0.6/docs/manual/core.html#health-checks