How to combine OpenTelemetry instrumentation with Elastic APM Agent features

Elastic APM supports OpenTelemetry on multiple levels. One easy-to understand scenario, which we previously blogged about, is the direct OpenTelemetry Protocol (OTLP) support in APM Server. This means that you can connect any OpenTelemetry agent to an Elastic APM Server and the APM Server will happily take that data, ingest it into Elasticsearch^®, and you can view that OpenTelemetry data in the APM app in Kibana^®.

This blog post will showcase a different use-case: within Elastic APM, we have our own APM Agents. Some of these have download numbers in the tens of millions, and some of them predate OpenTelemetry. Of course we realize OpenTelemetry is very important and it’s here to stay, so we wanted to make these agents OpenTelemetry compatible.

Most of our Elastic APM Agents today are able to ship OpenTelemetry spans as part of a trace. This means that if you have any component in your application that emits an OpenTelemetry span, it’ll be part of the trace the Elastic APM Agent captures. This can be a library you use that is already instrumented by the OpenTelemetry API, or it can be any other OpenTelemetry span that an application developer added into the application’s code for manual instrumentation.

This feature of the Elastic APM Agents not only reports those spans but also properly maintains parent-child relationships between all spans, making OpenTelemetry a first-class citizen for these agents. If, for example, an Elastic APM Agent starts a span for a specific action by auto-instrumentation and then within that span the OpenTelemetry API starts another span, then the OpenTelemetry span will be the child of the outer span created by the agent. This is reflected in the parent.id field of the spans. It’s the same the other way around as well: if a span is created by the OpenTelemetry API and within that span an Elastic APM agent captures another span, then the span created by the Elastic APM Agent will be the child of the other span created by the OpenTelemetry API.

This feature is present in the following agents: