# Distributed Tracing

Dapr uses OpenTelemetry (previously known as OpenCensus) for distributed traces and metrics collection. OpenTelemetry supports various backends including [Azure Monitor](https://azure.microsoft.com/en-us/services/monitor/), [Datadog](https://www.datadoghq.com), [Instana](https://www.instana.com), [Jaeger](https://www.jaegertracing.io/), [SignalFX](https://www.signalfx.com/), [Stackdriver](https://cloud.google.com/stackdriver), [Zipkin](https://zipkin.io) and others.

![Tracing](../../images/tracing.png)

## Contents

- [Tracing Design](#tracing-design)
- [Correlation ID](#correlation-id)
- [Configuration](#configuration)
- [References](#references)

## Tracing design

Dapr adds a HTTP/gRPC middleware to the Dapr sidecar. The middleware intercepts all Dapr and application traffic and automatically injects correlation IDs to trace distributed transactions. This design has several benefits:

* No need for code instrumentation. All traffic is automatically traced (with configurable tracing levels).
* Consistent tracing behavior across microservices. Tracing is configured and managed on Dapr sidecar so that it remains consistent across services made by different teams and potentially written in different programming languages.
* Configurable and extensible. By leveraging OpenTelemetry, Dapr tracing can be configured to work with popular tracing backends, including custom backends a customer may have.
* OpenTelemetry exporters are defined as first-class Dapr components. You can define and enable multiple exporters at the same time.

## Correlation ID

Dapr uses the standard W3C Trace Context headers. For HTTP requests, Dapr uses `traceparent` header.For gRPC requests, Dapr uses `grpc-trace-bin` header.When a request arrives without a trace ID, Dapr creates a new one. Otherwise, it passes the trace ID along the call chain.

## Configuration

Dapr tracing is configured by a configuration file (in local mode) or a Kubernetes configuration object (in Kubernetes mode). For example, the following configuration object enables distributed tracing:

```yaml
apiVersion: dapr.io/v1alpha1
kind: Configuration
metadata:
  name: tracing
spec:
  tracing:
    samplingRate: "1"
```

`samplingRate` is used to enable or disable the tracing. To disable the sampling rate ,
set `samplingRate : "0"` in the configuration. The valid range of samplingRate is between 0 and 1 inclusive. The sampling rate determines whether a trace span should be sampled or not based on vallue. `samplingRate : "1"` will always sample the traces.By default, the sampling rate is 1 in 10,000

Please see the [References](#references) section for more details on how to configure tracing on local environment and Kubernetes environment.

Dapr supports pluggable exporters, defined by configuration files (in local mode) or a Kubernetes custom resource object (in Kubernetes mode). For example, the following manifest defines a Zipkin exporter:

```yaml
apiVersion: dapr.io/v1alpha1
kind: Component
metadata:
  name: zipkin
spec:
  type: exporters.zipkin
  metadata:
  - name: enabled
    value: "true"
  - name: exporterAddress
    value: "http://zipkin.default.svc.cluster.local:9411/api/v2/spans"
```

## References

* [How-To: Set up Application Insights for distributed tracing](../../howto/diagnose-with-tracing/azure-monitor.md)
* [How-To: Set up Zipkin for distributed tracingn](../../howto/diagnose-with-tracing/zipkin.md)