First version of a Go gRPC Prometheus Interceptor
client/client.go calls our gRPC server SayHello method with two different values for the method parameter Name
server/server.go exposes and endpoint for the prometheus metrics and a grpc method SayHello which receives a Name param. The GRPC method has a unary interceptor for exposing two metrics: handled req counter and handled req histogram. The metrics are populated with three labels req service, req method and the value of the req param Name. For getting the value of req.Name we use a method func CustomLable(v {}interface) string which basically uses type assertion for casting the interface and getting the right value for the label. For each req type that we want to decorate with the custom label we will have to add a case in the switch statement. Oterwhise, the metrics are populated with the "unknown" label.
prometheus.yaml: prometheus configuration
Open three terminals and run
prometheus --config.file=prometheus.yaml # prometheus bin should be in your path
go run server.go
go run client.go
Open your browser and go to localhost:9090.