# Spring Boot otel.propagators

# Introduction

In Spring Boot applications utilizing OpenTelemetry for distributed tracing, `otel.propagators` is a configuration property used to specify which context propagation formats OpenTelemetry should use.

# W3C Trace Context

The `tracecontext` value for `otel.propagators` specifically refers to the W3C Trace Context specification. This is the recommended and default propagation format for OpenTelemetry. It defines a standard way to propagate trace and span IDs across service boundaries using HTTP headers, primarily `traceparent` and `tracestate`.

# How it works in Spring Boot:

-   **Instrumentation:**

    When OpenTelemetry instrumentation is enabled in your Spring Boot application (e.g., through the OpenTelemetry Spring Boot Starter), it automatically intercepts incoming and outgoing requests.

-   **Extraction:**

    For incoming requests, OpenTelemetry extracts the trace context information (trace ID, span ID, sampling state, etc.) from the `traceparent` and `tracestate` headers (if present). This extracted context is then made available to the current execution thread.

-   **Injection:**

    For outgoing requests (e.g., HTTP calls to other services), OpenTelemetry injects the current trace context into the `traceparent` and `tracestate` headers of the outgoing request. This ensures that the downstream service receives the necessary information to continue the trace.

## Configuration:

You can configure `otel.propagators` in your `application.properties` or `application.yml` file:

```
otel.propagators=tracecontext,baggage
```

```
otel:
  propagators: tracecontext,baggage
```

In this example, tracecontext is specified, along with baggage, which is another common propagation format used for propagating arbitrary key-value pairs across services.

# Conclusion

By using otel.propagators=tracecontext, you ensure that your Spring Boot application properly participates in distributed traces, allowing for end-to-end visibility of requests across multiple services.