This is a helper for RPC libraries such as gRPC and Dubbo. Specifically, this
includes samplers for clients and servers, configured with RpcTracing.
The RpcTracing class holds a reference to a tracing component and
sampling policy.
The default sampling policy is to use the default (trace ID) sampler for client and server requests.
For example, if there's a incoming request that has no trace IDs in its
headers, the sampler indicated by RpcTracing.Builder.serverSampler
decides whether or not to start a new trace. Once a trace is in progress, it is
used for any outgoing messages (client requests).
On the other hand, you may have outgoing requests didn't originate from a
server. For example, bootstrapping your application might call a discovery
service. In this case, the policy defined by RpcTracing.Builder.clientSampler
decides if a new trace will be started or not.
You can change the sampling policy by specifying it in the RpcTracing
component. The default implementation RpcRuleSampler allows you to
declare rules based on declare rules based on RPC properties and apply an
appropriate sampling rate.
Ex. Here's a sampler that traces 100 "Report" requests per second. This doesn't start new traces for requests to the scribe service. Other requests will use a global rate provided by the tracing component.
import static brave.rpc.RpcRequestMatchers.*;
rpcTracingBuilder.serverSampler(RpcRuleSampler.newBuilder()
.putRule(serviceEquals("scribe"), Sampler.NEVER_SAMPLE)
.putRule(methodEquals("Report"), RateLimitingSampler.create(100))
.build());Check for instrumentation written here and Zipkin's list before rolling your own Rpc instrumentation! Besides documentation here, you should look at the core library documentation as it covers topics including propagation. You may find our feature tests helpful, too.