Zipkin

Development and Testing Set-up

Great efforts have been made to make Zipkin easier to test, develop and experiment against. Zipkin can now be run from a single Docker container or by running its self-contained executable jar without extensive configuration. In its default configuration you will run Zipkin with a HTTP collector, In memory Span storage backend and web UI on port 9411.

Example:

docker run -d -p 9411:9411 openzipkin/zipkin

Instrumenting your services with Zipkin distributed tracing using the default configuration is now possible with the latest release of zipkin-go-opentracing as it includes an HTTP transport for sending spans to the Zipkin HTTP Collector.

Middleware Usage

Follow the addsvc example to check out how to wire the Zipkin Middleware. The changes should be relatively minor.

The zipkin-go-opentracing package has support for HTTP, Kafka and Scribe collectors as well as using Go Kit's Log package for logging.

Configuring for the Zipkin HTTP Collector

To select the transport for the HTTP Collector, you configure the Recorder with the appropriate collector like this:

var (
  debugMode          = false
  serviceName        = "MyService"
  serviceHostPort    = "localhost:8000"
  zipkinHTTPEndpoint = "localhost:9411"
)
collector, err = zipkin.NewHTTPCollector(zipkinHTTPEndpoint)
if err != nil {
  // handle error
}
tracer, err = zipkin.NewTracer(
  zipkin.NewRecorder(collector, debugMode, serviceHostPort, serviceName),
  ...
)

Span per Node vs. Span per RPC

By default Zipkin V1 considers either side of an RPC to have the same identity and differs in that respect from many other tracing systems which consider the caller to be the parent and the receiver to be the child. The OpenTracing specification does not dictate one model over the other, but the Zipkin team is looking into these single-host-spans to potentially bring Zipkin more in-line with the other tracing systems.

In case of a span per node the receiver will create a child span from the propagated parent span like this:

Span per Node propagation and identities

CALLER:            RECEIVER:
---------------------------------
traceId        ->  traceId
                   spanId (new)
spanId         ->  parentSpanId
parentSpanId

Note: most tracing implementations supporting the span per node model therefore do not propagate their parentSpanID as its not needed.

A typical Zipkin implementation will use the span per RPC model and recreate the span identity from the caller on the receiver's end and then annotates its values on top of it. Propagation will happen like this:

Span per RPC propagation and identities

CALLER:            RECEIVER:
---------------------------------
traceId        ->  traceId
spanId         ->  spanId
parentSpanId   ->  parentSpanId

The zipkin-go-opentracing implementation allows you to choose which model you wish to use. Make sure you select the same model consistently for all your services that are required to communicate with each other or you will have trace propagation issues. If using non OpenTracing / legacy instrumentation, it's probably best to use the span per RPC call model.

To adhere to the more common tracing philosophy of span per node, the Tracer defaults to span per node. To set the span per RPC call mode start your tracer like this:

tracer, err = zipkin.NewTracer(
	zipkin.NewRecorder(...),
	zipkin.ClientServerSameSpan(true),
)

Tracing Resources

In our legacy implementation we had the NewChildSpan method to allow annotation of resources such as databases, caches and other services that do not have server side tracing support. Since OpenTracing has no specific method of dealing with these items explicitely that is compatible with Zipkin's SA annotation, the zipkin-go-opentracing has implemented support using the OpenTracing Tags system. Here is an example of how one would be able to record a resource span compatible with standard OpenTracing and triggering an SA annotation in zipkin-go-opentracing:

// you need to import the ext package for the Tag helper functions
import (
	"github.com/opentracing/opentracing-go"
	"github.com/opentracing/opentracing-go/ext"
)

func (svc *Service) GetMeSomeExamples(ctx context.Context, ...) ([]Examples, error) {
	// Example of annotating a database query:
	var (
		serviceName = "MySQL"
		serviceHost = "mysql.example.com"
		servicePort = uint16(3306)
		queryLabel  = "GetExamplesByParam"
		query       = "select * from example where param = 'value'"
	)

	// retrieve the parent span, if not found create a new trace
	parentSpan := opentracing.SpanFromContext(ctx)
	if parentSpan == nil {
		parentSpan = opentracing.StartSpan(queryLabel)
    defer parentSpan.Finish()
	}

	// create a new span to record the resource interaction
	span := opentracing.StartChildSpan(parentSpan, queryLabel)

	// span.kind "resource" triggers SA annotation
	ext.SpanKind.Set(span, "resource")

	// this will label the span's service & hostPort (called Endpoint in Zipkin)
	ext.PeerService.Set(span, serviceName)
	ext.PeerHostname,Set(span, serviceHost)
	ext.PeerPort.Set(span, servicePort)

	// a Tag is the equivalent of a Zipkin Binary Annotation (key:value pair)
	span.SetTag("query", query)

	// a LogEvent is the equivalent of a Zipkin Annotation (timestamped)
	span.LogEvent("query:start")

	// do the actual query...

	// let's annotate the end...
	span.LogEvent("query:end")

	// we're done with this span.
	span.Finish()

	// do other stuff
	...
}

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