To reduce confusion and overhead, the following custom spring-messaging headers added in Sleuth 1.0 are no longer sent, and a log warning is issued once if they are by outside code.
* spanId
* spanSampled
* spanParentSpanId
* spanTraceId
* spanFlags
Sending the above headers actually increases the headers by up to 10 because they are duplicated in the "native" part of messages. This overhead is extreme especially if messages never leave the process.
The solution is to only send [b3 single format](https://github.com/openzipkin/b3-propagation#single-header), which has been in sleuth since 2.0 and is compatible with JMS. The B3 single format is always parsed and takes precedence, even if multiple headers are sent, so this is a safe change.
Note: Unlike RPC, messaging spans never join with their parent. Better performance is achieved by not propagating the producer's parentId downstream.
Note: Deprecated spring-messaging headers such "spanTraceId" as are still read in Sleuth 3.x. However, they will not be at some point in the future. Please pay attention to the log messages and update your code if you are accidentally using them.
* 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();
}
```
with the current setup we're using the MDC's default interpolation as a default for spring var resolution (which makes no sense)
with this change we're removing the dashes
fixes gh-1396
