Do we have to pass header values from WebClient in Zipkins - spring-cloud-sleuth

Question

I am using Spring boot and following libraries in client and server,
dependencyManagement {
imports {
mavenBom "org.springframework.cloud:spring-cloud-dependencies:Finchley.SR2"
}
}
// Spring Cloud Sleuth
compile group: 'org.springframework.cloud', name: 'spring-cloud-starter-sleuth', version: '2.0.1.RELEASE'
compile group: 'org.springframework.cloud', name: 'spring-cloud-starter-zipkin', version: '2.0.1.RELEASE'
Based upon spring documentation, "https://cloud.spring.io/spring-cloud-sleuth/"
Run this app and then hit the home page. You will see traceId and spanId populated in the logs. If this app calls out to another one (e.g. with RestTemplate) it will send the trace data in headers and if the receiver is another Sleuth app you will see the trace continue there.
How will this work with Spring5 web client?

Answer 1

It will work in the same way. It's enough to inject a bean of WebClient or WebClientBuilder type. Check out this sample https://github.com/spring-cloud-samples/sleuth-documentation-apps/blob/master/service1/src/main/java/io/spring/cloud/sleuth/docs/service1/Service2Client.java
/**
* #author Marcin Grzejszczak
*/
#Component
class Service2Client {
private static final Logger log = LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
private final WebClient webClient;
private final String serviceAddress;
private final Tracer tracer;
Service2Client(WebClient webClient,
#Value("${service2.address:localhost:8082}") String serviceAddress,
Tracer tracer) {
this.webClient = webClient;
this.serviceAddress = serviceAddress;
this.tracer = tracer;
}
public String start() throws InterruptedException {
log.info("Hello from service1. Setting baggage foo=>bar");
Span span = tracer.currentSpan();
String secretBaggage = ExtraFieldPropagation.get("baggage");
log.info("Super secret baggage item for key [baggage] is [{}]", secretBaggage);
if (StringUtils.hasText(secretBaggage)) {
span.annotate("secret_baggage_received");
span.tag("baggage", secretBaggage);
}
String baggageKey = "key";
String baggageValue = "foo";
ExtraFieldPropagation.set(baggageKey, baggageValue);
span.annotate("baggage_set");
span.tag(baggageKey, baggageValue);
log.info("Hello from service1. Calling service2");
String response = webClient.get()
.uri("http://" + serviceAddress + "/foo")
.exchange()
.block()
.bodyToMono(String.class).block();
Thread.sleep(100);
log.info("Got response from service2 [{}]", response);
log.info("Service1: Baggage for [key] is [" + ExtraFieldPropagation.get("key") + "]");
return response;
}
#NewSpan("first_span")
String timeout(#SpanTag("someTag") String tag) {
try {
Thread.sleep(300);
log.info("Hello from service1. Calling service2 - should end up with read timeout");
String response = webClient.get()
.uri("http://" + serviceAddress + "/readtimeout")
.retrieve()
.onStatus(httpStatus -> httpStatus.isError(), clientResponse -> {
throw new IllegalStateException("Exception!");
})
.bodyToMono(String.class)
.block();
log.info("Got response from service2 [{}]", response);
return response;
} catch (Exception e) {
log.error("Exception occurred while trying to send a request to service 2", e);
throw new RuntimeException(e);
}
}
}