orca/

ORCA Load Reporting

ORCA is a protocol for reporting load between servers and clients. This example shows how to implement this from both the client and server side. For more details, please see gRFC A51

Try it

go run server/main.go

go run client/main.go

Explanation

gRPC ORCA support provides two different ways to report load data to clients from servers: out-of-band and per-RPC. Out-of-band metrics are reported regularly at some interval on a stream, while per-RPC metrics are reported along with the trailers at the end of a call. Both of these mechanisms are optional and work independently.

The full ORCA API documentation is available here: https://pkg.go.dev/google.golang.org/grpc/orca

Out-of-band Metrics

The server registers an ORCA service that is used for out-of-band metrics. It does this by using orca.Register() and then setting metrics on the returned orca.Service using its methods.

The client receives out-of-band metrics via the LB policy. It receives callbacks to a listener by registering the listener on a SubConn via orca.RegisterOOBListener.

Per-RPC Metrics

The server is set up to report query cost metrics in its RPC handler. For per-RPC metrics to be reported, the gRPC server must be created with the orca.CallMetricsServerOption() option, and metrics are set by calling methods on the returned orca.CallMetricRecorder from orca.CallMetricRecorderFromContext().

The client performs one RPC per second. Per-RPC metrics are available for each call via the Done() callback returned from the LB policy's picker.