Distributed Tracing

Elastic APM supports distributed tracing to enable you to analyze performance through your microservices architecture by tracing all the requests from the initial web request to your front-end service, to queries made to your back-end services all in one view.

Distributed tracing is enabled by default in the RUM agent, however, it only includes requests made to the same origin. In order to include cross-origin requests you must set the distributedTracingOrigins configuration option.

For example, consider an application that is served from: https://example.com. By default, all of the HTTP requests made to https://example.com will be included in the trace. To also include requests made to: https://api.example.com, you would need to add the following configuration:

var apm = initApm({
  ...
  distributedTracingOrigins: ['https://api.example.com']
})

This effectively tells the agent to add the distributed tracing HTTP header (elastic-apm-traceparent) to requests made to https://api.example.com.

The RUM agent is only one of the components in a distributed trace, therefore, you need to properly configure other components in order to use distributed tracing. In our example above you need to make sure https://api.example.com can respond to requests that include the distributed tracing header.

Specifically, https://api.example.com will receive an OPTIONS request with the following headers:

Access-Control-Request-Headers: elastic-apm-traceparent
Access-Control-Request-Method: [request-method]
Origin: [request-origin]

And should respond to it with these headers:

Access-Control-Allow-Headers: elastic-apm-traceparent
Access-Control-Allow-Methods: [allowed-methods]
Access-Control-Allow-Origin: [request-origin]

To read more about cross-origin requests and why this process is necessary, please see the MDN page on Cross-Origin Resource Sharing.

To inculde the transactions generated by the back-end agents for the dynamically-generated initial HTML document, you should provide the following configuration options while initializing the RUM agent:

var apm = initApm({
    ...
    pageLoadTraceId: <trace-id>,
    pageLoadSpanId: <span-id>,
    pageLoadSampled: <is-sampled>
})

Our back-end agents provide APIs to extract this information, please refer to the documentation of the agent for more detail.