Added support for service discovery based Zipkin URL resolution

README.adoc

@@ -322,6 +322,7 @@ Example of setting baggage on a span:
 ----
 Span initialSpan = this.tracer.createSpan("span");
 initialSpan.setBaggageItem("foo", "bar");
+initialSpan.setBaggageItem("UPPER_CASE", "someValue");
 ----
 
 ===== Baggage vs. Span Tags

docs/src/main/asciidoc/spring-cloud-sleuth.adoc

@@ -484,6 +484,26 @@ Stream based span reporting).
 spring.zipkin.locator.discovery.enabled: true
 ----
 
+== Sending spans to Zipkin
+
+By default if you add `spring-cloud-starter-zipkin` as a dependency to your project,
+when the span is closed, it will be sent to Zipkin over HTTP. The communication
+is asynchronous. You can configure the URL by setting the `spring.zipkin.baseUrl`
+property as follows:
+
+[source,yaml]
+----
+spring.zipkin.baseUrl: http://192.168.99.100:9411/
+----
+
+If you want to find Zipkin via service discovery it's enough to pass the
+Zipkin's service id inside the URL (example for `zipkinserver` service id)
+
+[source,yaml]
+----
+spring.zipkin.baseUrl: http://zipkinserver/
+----
+
 == Span Data as Messages
 
 You can accumulate and send span data over

spring-cloud-sleuth-zipkin/src/main/java/org/springframework/cloud/sleuth/zipkin/ZipkinProperties.java

@@ -26,7 +26,10 @@ import org.springframework.boot.context.properties.ConfigurationProperties;
  */
 @ConfigurationProperties("spring.zipkin")
 public class ZipkinProperties {
-	/** URL of the zipkin query server instance. */
+	/** URL of the zipkin query server instance. You can also provide
+	 *  the service id of the Zipkin server if Zipkin's registered in
+	 *  service discovery (e.g. http://zipkinserver/)
+	 */
 	private String baseUrl = "http://localhost:9411/";
 	private boolean enabled = true;
 	private int flushInterval = 1;