1. Introduction

This example has seven spans. If you go to traces in Zipkin, you can see this number in the second trace, as shown in the following image:

However, if you pick a particular trace, you can see four spans, as shown in the following image:

	Note
	When you pick a particular trace, you see merged spans. That means that, if there were two spans sent to Zipkin with Server Received and Server Sent or Client Received and Client Sent annotations, they are presented as a single span.

Why is there a difference between the seven and four spans in this case?

So, if we count the physical spans, we have one from http:/start, two from service1 calling service2, two from service2 calling service3, and two from service2 calling service4. In sum, we have a total of seven spans.

Logically, we see the information of four total Spans because we have one span related to the incoming request to service1 and three spans related to RPC calls.

Zipkin lets you visualize errors in your trace. When an exception was thrown and was not caught, we set proper tags on the span, which Zipkin can then properly colorize. You could see in the list of traces one trace that is red. That appears because an exception was thrown.

If you click that trace, you see a similar picture, as follows:

If you then click on one of the spans, you see the following

The span shows the reason for the error and the whole stack trace related to it.

Starting with version 2.0.0, Spring Cloud Sleuth uses Brave as the tracing library. Consequently, Sleuth no longer takes care of storing the context but delegates that work to Brave.

Due to the fact that Sleuth had different naming and tagging conventions than Brave, we decided to follow Brave’s conventions from now on. However, if you want to use the legacy Sleuth approaches, you can set the spring.sleuth.http.legacy.enabled property to true.

Figure 1.1. Click the Pivotal Web Services icon to see it live!

Click here to see it live!

The dependency graph in Zipkin should resemble the following image:

Figure 1.2. Click the Pivotal Web Services icon to see it live!

Click here to see it live!

When using grep to read the logs of those four applications by scanning for a trace ID equal to (for example) 2485ec27856c56f4, you get output resembling the following:

service1.log:2016-02-26 11:15:47.561  INFO [service1,2485ec27856c56f4,2485ec27856c56f4,true] 68058 --- [nio-8081-exec-1] i.s.c.sleuth.docs.service1.Application   : Hello from service1. Calling service2
service2.log:2016-02-26 11:15:47.710  INFO [service2,2485ec27856c56f4,9aa10ee6fbde75fa,true] 68059 --- [nio-8082-exec-1] i.s.c.sleuth.docs.service2.Application   : Hello from service2. Calling service3 and then service4
service3.log:2016-02-26 11:15:47.895  INFO [service3,2485ec27856c56f4,1210be13194bfe5,true] 68060 --- [nio-8083-exec-1] i.s.c.sleuth.docs.service3.Application   : Hello from service3
service2.log:2016-02-26 11:15:47.924  INFO [service2,2485ec27856c56f4,9aa10ee6fbde75fa,true] 68059 --- [nio-8082-exec-1] i.s.c.sleuth.docs.service2.Application   : Got response from service3 [Hello from service3]
service4.log:2016-02-26 11:15:48.134  INFO [service4,2485ec27856c56f4,1b1845262ffba49d,true] 68061 --- [nio-8084-exec-1] i.s.c.sleuth.docs.service4.Application   : Hello from service4
service2.log:2016-02-26 11:15:48.156  INFO [service2,2485ec27856c56f4,9aa10ee6fbde75fa,true] 68059 --- [nio-8082-exec-1] i.s.c.sleuth.docs.service2.Application   : Got response from service4 [Hello from service4]
service1.log:2016-02-26 11:15:48.182  INFO [service1,2485ec27856c56f4,2485ec27856c56f4,true] 68058 --- [nio-8081-exec-1] i.s.c.sleuth.docs.service1.Application   : Got response from service2 [Hello from service2, response from service3 [Hello from service3] and from service4 [Hello from service4]]

If you use a log aggregating tool (such as Kibana, Splunk, and others), you can order the events that took place. An example from Kibana would resemble the following image:

If you want to use Logstash, the following listing shows the Grok pattern for Logstash:

filter {
       # pattern matching logback pattern
       grok {
              match => { "message" => "%{TIMESTAMP_ISO8601:timestamp}\s+%{LOGLEVEL:severity}\s+\[%{DATA:service},%{DATA:trace},%{DATA:span},%{DATA:exportable}\]\s+%{DATA:pid}\s+---\s+\[%{DATA:thread}\]\s+%{DATA:class}\s+:\s+%{GREEDYDATA:rest}" }
       }
}

	Note
	If you want to use Grok together with the logs from Cloud Foundry, you have to use the following pattern:

filter {
       # pattern matching logback pattern
       grok {
              match => { "message" => "(?m)OUT\s+%{TIMESTAMP_ISO8601:timestamp}\s+%{LOGLEVEL:severity}\s+\[%{DATA:service},%{DATA:trace},%{DATA:span},%{DATA:exportable}\]\s+%{DATA:pid}\s+---\s+\[%{DATA:thread}\]\s+%{DATA:class}\s+:\s+%{GREEDYDATA:rest}" }
       }
}

JSON Logback with Logstash

Often, you do not want to store your logs in a text file but in a JSON file that Logstash can immediately pick. To do so, you have to do the following (for readability, we pass the dependencies in the groupId:artifactId:version notation).

Dependencies Setup

1. Ensure that Logback is on the classpath (ch.qos.logback:logback-core).
2. Add Logstash Logback encode. For example, to use version 4.6, add net.logstash.logback:logstash-logback-encoder:4.6.

Logback Setup

Consider the following example of a Logback configuration file (named logback-spring.xml).

<?xml version="1.0" encoding="UTF-8"?>
<configuration>
	<include resource="org/springframework/boot/logging/logback/defaults.xml"/>
	​
	<springProperty scope="context" name="springAppName" source="spring.application.name"/>
	<!-- Example for logging into the build folder of your project -->
	<property name="LOG_FILE" value="${BUILD_FOLDER:-build}/${springAppName}"/>​

	<!-- You can override this to have a custom pattern -->
	<property name="CONSOLE_LOG_PATTERN"
			  value="%clr(%d{yyyy-MM-dd HH:mm:ss.SSS}){faint} %clr(${LOG_LEVEL_PATTERN:-%5p}) %clr(${PID:- }){magenta} %clr(---){faint} %clr([%15.15t]){faint} %clr(%-40.40logger{39}){cyan} %clr(:){faint} %m%n${LOG_EXCEPTION_CONVERSION_WORD:-%wEx}"/>

	<!-- Appender to log to console -->
	<appender name="console" class="ch.qos.logback.core.ConsoleAppender">
		<filter class="ch.qos.logback.classic.filter.ThresholdFilter">
			<!-- Minimum logging level to be presented in the console logs-->
			<level>DEBUG</level>
		</filter>
		<encoder>
			<pattern>${CONSOLE_LOG_PATTERN}</pattern>
			<charset>utf8</charset>
		</encoder>
	</appender>

	<!-- Appender to log to file -->​
	<appender name="flatfile" class="ch.qos.logback.core.rolling.RollingFileAppender">
		<file>${LOG_FILE}</file>
		<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
			<fileNamePattern>${LOG_FILE}.%d{yyyy-MM-dd}.gz</fileNamePattern>
			<maxHistory>7</maxHistory>
		</rollingPolicy>
		<encoder>
			<pattern>${CONSOLE_LOG_PATTERN}</pattern>
			<charset>utf8</charset>
		</encoder>
	</appender>
	​
	<!-- Appender to log to file in a JSON format -->
	<appender name="logstash" class="ch.qos.logback.core.rolling.RollingFileAppender">
		<file>${LOG_FILE}.json</file>
		<rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
			<fileNamePattern>${LOG_FILE}.json.%d{yyyy-MM-dd}.gz</fileNamePattern>
			<maxHistory>7</maxHistory>
		</rollingPolicy>
		<encoder class="net.logstash.logback.encoder.LoggingEventCompositeJsonEncoder">
			<providers>
				<timestamp>
					<timeZone>UTC</timeZone>
				</timestamp>
				<pattern>
					<pattern>
						{
						"severity": "%level",
						"service": "${springAppName:-}",
						"trace": "%X{X-B3-TraceId:-}",
						"span": "%X{X-B3-SpanId:-}",
						"parent": "%X{X-B3-ParentSpanId:-}",
						"exportable": "%X{X-Span-Export:-}",
						"pid": "${PID:-}",
						"thread": "%thread",
						"class": "%logger{40}",
						"rest": "%message"
						}
					</pattern>
				</pattern>
			</providers>
		</encoder>
	</appender>
	​
	<root level="INFO">
		<appender-ref ref="console"/>
		<!-- uncomment this to have also JSON logs -->
		<!--<appender-ref ref="logstash"/>-->
		<!--<appender-ref ref="flatfile"/>-->
	</root>
</configuration>

That Logback configuration file:

• Logs information from the application in a JSON format to a build/${spring.application.name}.json file.
• Has commented out two additional appenders: console and standard log file.
• Has the same logging pattern as the one presented in the previous section.

	Note
	If you use a custom logback-spring.xml, you must pass the spring.application.name in the bootstrap rather than the application property file. Otherwise, your custom logback file does not properly read the property.

The span context is the state that must get propagated to any child spans across process boundaries. Part of the Span Context is the Baggage. The trace and span IDs are a required part of the span context. Baggage is an optional part.

Baggage is a set of key:value pairs stored in the span context. Baggage travels together with the trace and is attached to every span. Spring Cloud Sleuth understands that a header is baggage-related if the HTTP header is prefixed with baggage- and, for messaging, it starts with baggage_.

	Important
	There is currently no limitation of the count or size of baggage items. However, keep in mind that too many can decrease system throughput or increase RPC latency. In extreme cases, too much baggage can crash the application, due to exceeding transport-level message or header capacity.

The following example shows setting baggage on a span:

Span initialSpan = this.tracer.nextSpan().name("span").start();
try (Tracer.SpanInScope ws = this.tracer.withSpanInScope(initialSpan)) {
	ExtraFieldPropagation.set("foo", "bar");
	ExtraFieldPropagation.set("UPPER_CASE", "someValue");
}

Baggage versus Span Tags

Baggage travels with the trace (every child span contains the baggage of its parent). Zipkin has no knowledge of baggage and does not receive that information.

	Important
	Starting from Sleuth 2.0.0 you have to pass the baggage key names explicitly in your project configuration. Read more about that setup here

Tags are attached to a specific span. In other words, they are presented only for that particular span. However, you can search by tag to find the trace, assuming a span having the searched tag value exists.

If you want to be able to lookup a span based on baggage, you should add a corresponding entry as a tag in the root span.

	Important
	The span must be in scope.

The following listing shows integration tests that use baggage:

The setup. 

spring.sleuth:
  baggage-keys:
    - baz
    - bizarrecase
  propagation-keys:
    - foo
    - upper_case

The code. 

initialSpan.tag("foo",
		ExtraFieldPropagation.get(initialSpan.context(), "foo"));
initialSpan.tag("UPPER_CASE",
		ExtraFieldPropagation.get(initialSpan.context(), "UPPER_CASE"));

If you want to use only Spring Cloud Sleuth without the Zipkin integration, add the spring-cloud-starter-sleuth module to your project.

The following example shows how to add Sleuth with Maven:

Maven. 

<dependencyManagement> 
      <dependencies>
          <dependency>
              <groupId>org.springframework.cloud</groupId>
              <artifactId>spring-cloud-dependencies</artifactId>
              <version>${release.train.version}</version>
              <type>pom</type>
              <scope>import</scope>
          </dependency>
      </dependencies>
</dependencyManagement>

<dependency> 
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-sleuth</artifactId>
</dependency>

The following example shows how to add Sleuth with Gradle:

Gradle. 

dependencyManagement { 
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${releaseTrainVersion}"
    }
}

dependencies { 
    compile "org.springframework.cloud:spring-cloud-starter-sleuth"
}

If you want both Sleuth and Zipkin, add the spring-cloud-starter-zipkin dependency.

The following example shows how to do so for Maven:

Maven. 

<dependencyManagement> 
      <dependencies>
          <dependency>
              <groupId>org.springframework.cloud</groupId>
              <artifactId>spring-cloud-dependencies</artifactId>
              <version>${release.train.version}</version>
              <type>pom</type>
              <scope>import</scope>
          </dependency>
      </dependencies>
</dependencyManagement>

<dependency> 
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-zipkin</artifactId>
</dependency>

The following example shows how to do so for Gradle:

Gradle. 

dependencyManagement { 
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${releaseTrainVersion}"
    }
}

dependencies { 
    compile "org.springframework.cloud:spring-cloud-starter-zipkin"
}

If you want to use RabbitMQ or Kafka instead of HTTP, add the spring-rabbit or spring-kafka dependency. The default destination name is zipkin.

If using Kafka, you must set the property spring.zipkin.sender.type property accordingly:

spring.zipkin.sender.type: kafka

	Caution
	spring-cloud-sleuth-stream is deprecated and incompatible with these destinations.

If you want Sleuth over RabbitMQ, add the spring-cloud-starter-zipkin and spring-rabbit dependencies.

The following example shows how to do so for Gradle:

Maven. 

<dependencyManagement> 
      <dependencies>
          <dependency>
              <groupId>org.springframework.cloud</groupId>
              <artifactId>spring-cloud-dependencies</artifactId>
              <version>${release.train.version}</version>
              <type>pom</type>
              <scope>import</scope>
          </dependency>
      </dependencies>
</dependencyManagement>

<dependency> 
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-zipkin</artifactId>
</dependency>
<dependency> 
    <groupId>org.springframework.amqp</groupId>
    <artifactId>spring-rabbit</artifactId>
</dependency>

Gradle. 

dependencyManagement { 
    imports {
        mavenBom "org.springframework.cloud:spring-cloud-dependencies:${releaseTrainVersion}"
    }
}

dependencies {
    compile "org.springframework.cloud:spring-cloud-starter-zipkin" 
    compile "org.springframework.amqp:spring-rabbit" 
}