Traces

A trace is a group of transactions and spans with a common root. Each trace tracks the entirety of a single request. It describes the individual operations and their causality that ensue from a single logical operation.

Distributed tracing

When a trace travels through multiple services, as is common in a microservice architecture, it is known as a distributed trace. A distributed trace comprises operations across multiple distributed components, crossing process, network, and security boundaries.

Why is distributed tracing important?

Distributed tracing enables you to analyze performance throughout your microservice architecture by tracing the entirety of a request — from the initial web request on your front-end service all the way to database queries made on your back-end services.

Tracking requests as they propagate through your services provides an end-to-end picture of where your application is spending time, where errors are occurring, and where bottlenecks are forming. Distributed tracing eliminates individual service’s data silos and reveals what’s happening outside of service borders.

For supported technologies, distributed tracing works out-of-the-box, with no additional configuration required.

How distributed tracing works

Distributed tracing works by injecting a custom traceparent HTTP header into outgoing requests. This header includes information, like trace-id, which is used to identify the current trace, and parent-id, which is used to identify the parent of the current span on incoming requests or the current span on an outgoing request.

When a service is working on a request, it checks for the existence of this HTTP header. If it’s missing, the service starts a new trace. If it exists, the service ensures the current action is added as a child of the existing trace, and continues to propagate the trace.

Trace propagation examples

In this example, Elastic’s Ruby agent communicates with Elastic’s Java agent. Both support the traceparent header, and trace data is successfully propagated.

In this example, Elastic’s Ruby agent communicates with OpenTelemetry’s Java agent. Both support the traceparent header, and trace data is successfully propagated.

In this example, the trace meets a piece of middleware that doesn’t propagate the traceparent header. The distributed trace ends and any further communication will result in a new trace.

W3C Trace Context specification

All Elastic agents now support the official W3C Trace Context specification and traceparent header. See the table below for the minimum required agent version:

Agent name	Agent Version
Go Agent	≥1.6
Java Agent	≥1.14
.NET Agent	≥1.3
Node.js Agent	≥3.4
PHP Agent	≥1.0
Python Agent	≥5.4
Ruby Agent	≥3.5
RUM Agent	≥5.0

Note

Older Elastic agents use a unique elastic-apm-traceparent header. For backward-compatibility purposes, new versions of Elastic agents still support this header.

Visualize distributed tracing

The Applications UI’s timeline visualization provides a visual deep-dive into each of your application’s traces:

Manual distributed tracing

Elastic agents automatically propagate distributed tracing context for supported technologies. If your service communicates over a different, unsupported protocol, you can manually propagate distributed tracing context from a sending service to a receiving service with each agent’s API.

Add the traceparent header to outgoing requests

Sending services must add the traceparent header to outgoing requests.

Android

Not applicable.

Go

1. Start a transaction with StartTransaction or a span with StartSpan.
2. Get the active TraceContext.
3. Send the TraceContext to the receiving service.

Example:

			transaction := apm.DefaultTracer().StartTransaction("GET /", "request") 1
traceContext := transaction.TraceContext() 2

// Send TraceContext to receiving service
traceparent := apmhttp.FormatTraceparentHeader(traceContext) 3
tracestate := traceContext.State.String()

		

1. Start a transaction
2. Get TraceContext from current Transaction
3. Format the TraceContext or tracestate as a traceparent header.

iOS

The agent will automatically inject trace headers into network requests using URLSessions, but if you’re using a non-standard network library you may need to manually inject them. It will be done using the OpenTelemetry APIs:

1. Create a Setter
2. Create a Span per Open Telemetry standards
3. Inject trace context to header dictionary
4. Follow the procedure of your network library to complete the network request. Make sure to call span.end() when the request succeeds or fails.

			import OpenTelemetryApi
import OpenTelemetrySdk

struct BasicSetter: Setter {
    func set(carrier: inout [String: String], key: String, value: String) {
        carrier[key] = value
    }
}

let span : Span = ...
let setter = BasicSetter()
let propagator = W3CTraceContextPropagator()
var headers = [String:String]()

propagator.inject(spanContext: span.context, carrier: &headers, setter:setter)

let request = URLRequest(...)
request.allHTTPHeaderFields = headers
...
span.end()

		

Java

1. Start a transaction with startTransaction, or a span with startSpan.
2. Inject the traceparent header into the request object with injectTraceHeaders
3. make network request

Example of manually instrumenting an RPC framework:

			// Hook into a callback provided by the RPC framework that is called on outgoing requests
public Response onOutgoingRequest(Request request) throws Exception {
  Span span = ElasticApm.currentSpan() 1
          .startSpan("external", "http", null)
          .setName(request.getMethod() + " " + request.getHost());
  try (final Scope scope = transaction.activate()) {
      span.injectTraceHeaders((name, value) -> request.addHeader(name, value)); 2
      return request.execute();
  } catch (Exception e) {
      span.captureException(e);
      throw e;
  } finally {
      span.end(); 3
  }
}

		

1. Create a span representing an external call
2. Inject the traceparent header into the request object
3. End the span

.NET

1. Serialize the distributed tracing context of the active transaction or span with CurrentTransaction or CurrentSpan.
2. Send the serialized context the receiving service.

Example:

			string outgoingDistributedTracingData =
    (Agent.Tracer.CurrentSpan?.OutgoingDistributedTracingData
        ?? Agent.Tracer.CurrentTransaction?.OutgoingDistributedTracingData)?.SerializeToString();
// Now send `outgoingDistributedTracingData` to the receiving service

		

Node.js

1. Start a transaction with apm.startTransaction(), or a span with apm.startSpan().
2. Get the serialized traceparent string of the started transaction/span with currentTraceparent.
3. Encode the traceparent and send it to the receiving service inside your regular request.

Example using raw UDP to communicate between two services, A and B:

			agent.startTransaction('my-service-a-transaction'); 1
const traceparent = agent.currentTraceparent; 2
sendMetadata(`traceparent: ${traceparent}\n`); 3

		

1. Start a transaction
2. Get the current traceparent
3. Send the traceparent as a header to service B.

PHP

1. On the client side (i.e., the side sending the request) get the current distributed tracing context.
2. Serialize the current distributed tracing context to a format supported by the request’s transport and send it to the server side (i.e., the side receiving the request).

Example:

			$distDataAsString = ElasticApm::getSerializedCurrentDistributedTracingData(); 1

		

1. Get the current distributed tracing data serialized as string

Python

1. Start a transaction with begin_transaction().
2. Get the trace_parent of the active transaction.
3. Send the trace_parent to the receiving service.

Example:

			client.begin_transaction('new-transaction')<1>

elasticapm.get_trace_parent_header('new-transaction') 2

# Send `trace_parent_str` to another service

		

1. Start a new transaction
2. Return the string representation of the current transaction’s TraceParent object

Ruby

1. Start a span with with_span.
2. Get the active TraceContext.
3. Send the TraceContext to the receiving service.

			ElasticAPM.with_span "Name" do |span| 1
  header = span.trace_context.traceparent.to_header 2
  # send the TraceContext Header to a receiving service...
end

		

1. Start a span
2. Get the TraceContext

Parse the traceparent header on incoming requests

Receiving services must parse the incoming traceparent header, and start a new transaction or span as a child of the received context.

Android

Not applicable.

Go

1. Parse the incoming TraceContext with ParseTraceparentHeader or ParseTracestateHeader.
2. Start a new transaction or span as a child of the incoming transaction with StartTransactionOptions or StartSpanOptions.

Example:

			// Receive incoming TraceContext
traceContext, _ := apmhttp.ParseTraceparentHeader(r.Header.Get("Traceparent")) 1
traceContext.State, _ = apmhttp.ParseTracestateHeader(r.Header["Tracestate"]...) 2

opts := apm.TransactionOptions{
	TraceContext: traceContext, 3
}
transaction := apm.DefaultTracer().StartTransactionOptions("GET /", "request", opts) 4

		

1. Parse the TraceParent header
2. Parse the Tracestate header
3. Set the parent trace context
4. Start a new transaction as a child of the received TraceContext

iOS

Not applicable.

Java

1. Create a transaction as a child of the incoming transaction with startTransactionWithRemoteParent().
2. Start and name the transaction with activate() and setName().

Example:

			// Hook into a callback provided by the framework that is called on incoming requests
public Response onIncomingRequest(Request request) throws Exception {
    // creates a transaction representing the server-side handling of the request
    Transaction transaction = ElasticApm.startTransactionWithRemoteParent(request::getHeader, request::getHeaders); 1
    try (final Scope scope = transaction.activate()) { 2
        String name = "a useful name like ClassName#methodName where the request is handled";
        transaction.setName(name); 3
        transaction.setType(Transaction.TYPE_REQUEST); 4
        return request.handle();
    } catch (Exception e) {
        transaction.captureException(e);
        throw e;
    } finally {
        transaction.end(); 5
    }
}

		

1. Create a transaction as the child of a remote parent
2. Activate the transaction
3. Name the transaction
4. Add a transaction type
5. Eventually, end the transaction

.NET

Deserialize the incoming distributed tracing context, and pass it to any of the StartTransaction or CaptureTransaction APIs — all of which have an optional DistributedTracingData parameter. This will create a new transaction or span as a child of the incoming trace context.

Example starting a new transaction:

			var transaction2 = Agent.Tracer.StartTransaction("Transaction2", "TestTransaction",
     DistributedTracingData.TryDeserializeFromString(serializedDistributedTracingData));

		

Node.js

1. Decode and store the traceparent in the receiving service.
2. Pass in the traceparent as the childOf option to manually start a new transaction as a child of the received traceparent with apm.startTransaction().

Example receiving a traceparent over raw UDP:

			const traceparent = readTraceparentFromUDPPacket() 1
agent.startTransaction('my-service-b-transaction', { childOf: traceparent }) 2

		

1. Read the traceparent from the incoming request.
2. Use the traceparent to initialize a new transaction that is a child of the original traceparent.

PHP

1. Receive the distributed tracing data on the server side.
2. Begin a new transaction using the agent’s public API. For example, use ElasticApm::beginCurrentTransaction and pass the received distributed tracing data (serialized as string) as a parameter. This will create a new transaction as a child of the incoming trace context.
3. Don’t forget to eventually end the transaction on the server side.

Example:

			$receiverTransaction = ElasticApm::beginCurrentTransaction( 1
    'GET /data-api',
    'data-layer',
    /* timestamp */ null,
    $distDataAsString 2
);

		

1. Start a new transaction
2. Pass in the received distributed tracing data (serialized as string)

Once this new transaction has been created in the receiving service, you can create child spans, or use any other agent API methods as you typically would.

Python

1. Create a TraceParent object from a string or HTTP header.
2. Start a new transaction as a child of the TraceParent by passing in a TraceParent object.

Example using HTTP headers:

			parent = elasticapm.trace_parent_from_headers(headers_dict) 1
client.begin_transaction('processors', trace_parent=parent) 2

		

1. Create a TraceParent object from HTTP headers formed as a dictionary
2. Begin a new transaction as a child of the received TraceParent

Tip

See the TraceParent API for additional examples.

Ruby

Start a new transaction or span as a child of the incoming transaction or span with with_transaction or with_span.

Example:

			# env being a Rack env
context = ElasticAPM::TraceContext.parse(env: env) 1

ElasticAPM.with_transaction("Do things", trace_context: context) do 2
  ElasticAPM.with_span("Do nested thing", trace_context: context) do 3
  end
end

		

1. Parse the incoming TraceContext
2. Create a transaction as a child of the incoming TraceContext
3. Create a span as a child of the newly created transaction. trace_context is optional here, as spans are automatically created as a child of their parent’s transaction’s TraceContext when none is passed.

Distributed tracing with RUM

Some additional setup may be required to correlate requests correctly with the Real User Monitoring (RUM) agent.

See the RUM distributed tracing guide for information on enabling cross-origin requests, setting up server configuration, and working with dynamically-generated HTML.