* Add optional SC LoadBalancer dependency. Create TraceFeignBlockingLoadBalancerClient.
* Instrument Spring Cloud LoadBalancer in TraceFeignObjectWrapper.
* Do not use class in field in order to avoid NoClassDefFound.
fixes#1528
This switches to pass around and use `TraceContext` instead of `Span` in
Reactor's context to take advantage of `maybeScope` which is far cheaper
than `withSpanInScope` when the span is already current. This also kills
some extra scope checks and any other accidental calls noticed.
The performance improvement here, I can't quantify as haven't done any
JMH on it.
* Updates to latest Sampling infrastructure
Brave recently switched to an interface model for higher level sampling
like HTTP. So, `HttpSampler` -> `SamplingFunction<HttpRequest>`. Don't
worry because `HttpSampler` was retrofitted as a `SamplingFunction`.
This change moves to the higher interface, avoiding deprecated methods
and such. More interestingly, this weaves in support for `RpcTracing`,
which *finally* introduces RPC sampling the same way. Specifically, this
adds `SamplingFunction<RpcRequest>` under the same conventions as HTTP.
Most immediately, this can be used here in gRPC and Dubbo, as
autoconfiguration exists. It also works with any autoconfiguration that
isn't here, such as Armeria.
Ex. Here's a sampler that traces 100 "GetUserToken" requests per second. This
doesn't start new traces for requests to the health check service. Other
requests will use a global rate provided by the tracing component.
```java
import static brave.rpc.RpcRequestMatchers.methodEquals;
import static brave.rpc.RpcRequestMatchers.serviceEquals;
import static brave.sampler.Matchers.and;
--snip--
@Bean(name = ServerSampler.NAME)
SamplerFunction<RpcRequest> myRpcSampler() {
Matcher<RpcRequest> userAuth = and(
serviceEquals("users.UserService"),
methodEquals("GetUserToken")
);
return RpcRuleSampler.newBuilder()
.putRule(serviceEquals("grpc.health.v1.Health"), Sampler.NEVER_SAMPLE)
.putRule(userAuth, RateLimitingSampler.create(100)).build();
}
```
without this change there was a propagation gap due to additional quotes in the headers
with this change we're wrapping the DefaultKafkaHeaderMapper to not add additional quotes
fixes gh-1430
