Remote Procedure Call (RPC)

HealthCheckThread is replaced by StartHealthCheck function in socket.cpp, but some of the docs/comments are not modified correspondingly. There are 3 files that HealthCheckThread is involved in:

• test/brpc_socket_unittest.cpp(3 occurrences)
• docs/cn/load_balancing.md(1 occurrence)
• src/brpc/socket.h(1 occurrence)

All sentences with 'HealthCheckThread' should be rewritten to sync with the

The MinSendBackupAfterMs is now set to 1 ms. Unfortunately this causes backup requests to be send when there is low load. It would be useful if we could set the minimum a little bit higher for certain endpoints.

Currently, UnframedGrpcService returns an error message as plain text.
https://github.com/line/armeria/blob/54b70906bcd813f0b9b2c6715ad4086160ac49b2/grpc/src/main/java/com/linecorp/armeria/server/grpc/UnframedGrpcService.java#L255-L272
It would be nice to return a JSON object if the content type is JSON compatible.

{ 
   "code": "FAILED_PRECONDITION",
   "message": "Input validatio