Creating and using gRPC HealthCheck encoded wireformat with curl

2022-06-06

this is just a small cli tool that will help you construct a gRPC HealthCheck Request in its uncompressed wireformat

This utility will basically let you create a binary format of a grpc request which you can use with curl.

If you send the binary to a destination gRPC server that accepts healthchecks for a given service name. You can take the response back and check to see if the service is running or not.

Ofcourse almost 99% of the time you’d “just use” the gRPC healthcheck stub but there are occasions where the caller may not have all that setup (eg a loadbalancer’s healthcheck system that supports just HTTP and not gRPDC)

Anyway, this is something that i just wrote up this morning based on some work here

gRPC Request

To use

# download the proto
wget https://raw.githubusercontent.com/grpc/grpc/master/src/proto/grpc/health/v1/health.proto

# compile the proto
protoc  --descriptor_set_out=health.pb health.proto

# run the client and specify the serviceName you want to healtcheck
$ go run grpc_hc_wireformat.go --serviceName echo.EchoServer
Loading package v1
  Registering MessageType: HealthCheckRequest
  Registering MessageType: HealthCheckResponse
HealthCheckRequest: service:"echo.EchoServer"
Encoded HealthCheckRequest using protoreflect 0a0f6563686f2e4563686f536572766572
wire encoded HealthCheckRequest: 00000000110a0f6563686f2e4563686f536572766572

The output is the wireencoded format of a specific healthcheck

You can then use that wire formatted message in curl and dump the output.

In the following, i’m using a cloud run grpc server i host that hosts that specific service and healthchecks.

$ echo -n '00000000110a0f6563686f2e4563686f536572766572' | xxd -r -p - frame.bin
$ curl -s  --raw -X POST  \
   --http2-prior-knowledge \
   -H "Content-Type: application/grpc" \
   -H "TE: trailers"  \
   --data-binary @frame.bin \
   https://grpc-server-6w42z6vi3q-uc.a.run.app:443/grpc.health.v1.Health/Check  -o resp.bin

You can take the response and decode it:

$ xxd -p resp.bin 
 00000000020801

$ echo -n "0801" | xxd -r -p | protoc --decode grpc.health.v1.HealthCheckResponse  health.proto  
status: SERVING

The specific cloud run service will randomly (10% of times) return an UNHEALTHY response so you can use that to test as well

Thats it.

Also see:

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