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Distributed tracing

Understand how a single request that travels through multiple services impacts your application.

A trace is a group of transactions and spans with a common root. Each trace tracks the entirety of a single request. When a trace travels through multiple services, as is common in a microservice architecture, it is known as a distributed trace.

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 nameAgent 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

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

APM'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.

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

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.

  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"))
traceContext.State, _ = apmhttp.ParseTracestateHeader(r.Header["Tracestate"]...)
opts := apm.TransactionOptions{
TraceContext: traceContext,
}
transaction := apm.DefaultTracer.StartTransactionOptions("GET /", "request", opts)

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