# OpenTelemetry Tracing SDK

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The `tracing` module contains the foundation for all tracing SDKs of [opentelemetry-js](https://github.com/open-telemetry/opentelemetry-js).

Used standalone, this module provides methods for manual instrumentation of code, offering full control over span creation for client-side JavaScript (browser) and Node.js.

It does **not** provide automated instrumentation of known libraries, context propagation for asynchronous invocations or distributed-context out-of-the-box.

For automated instrumentation for Node.js, please see
[@opentelemetry/node](https://github.com/open-telemetry/opentelemetry-js/tree/master/packages/opentelemetry-node).

## Installation

```bash
npm install --save @opentelemetry/api
npm install --save @opentelemetry/tracing
```

## Usage

```js
const opentelemetry = require('@opentelemetry/api');
const { BasicTracerProvider } = require('@opentelemetry/tracing');

// To start a trace, you first need to initialize the Tracer provider.
// NOTE: The default OpenTelemetry tracer provider does not record any tracing information.
//       Registering a working tracer provider allows the API methods to record traces.
new BasicTracerProvider().register();

// To create a span in a trace, we used the global singleton tracer to start a new span.
const span = opentelemetry.trace.getTracer('default').startSpan('foo');

// Set a span attribute
span.setAttribute('key', 'value');

// We must end the spans so they become available for exporting.
span.end();
```

## Config

Tracing configuration is a merge of user supplied configuration with both the default
configuration as specified in [config.ts](./src/config.ts) and an
environmentally configurable (via `OTEL_SAMPLING_PROBABILITY`) probability
sampler delegate of a [ParentOrElse](https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/trace/sdk.md#parentorelse) sampler.

## Example

See [examples/basic-tracer-node](https://github.com/open-telemetry/opentelemetry-js/tree/master/examples/basic-tracer-node) for an end-to-end example, including exporting created spans.

## Useful links

- For more information on OpenTelemetry, visit: <https://opentelemetry.io/>
- For more about OpenTelemetry JavaScript: <https://github.com/open-telemetry/opentelemetry-js>
- For help or feedback on this project, join us on [gitter][gitter-url]

## License

Apache 2.0 - See [LICENSE][license-url] for more information.

[gitter-image]: https://badges.gitter.im/open-telemetry/opentelemetry-js.svg
[gitter-url]: https://gitter.im/open-telemetry/opentelemetry-node?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge
[license-url]: https://github.com/open-telemetry/opentelemetry-js/blob/master/LICENSE
[license-image]: https://img.shields.io/badge/license-Apache_2.0-green.svg?style=flat
[dependencies-image]: https://david-dm.org/open-telemetry/opentelemetry-js/status.svg?path=packages/opentelemetry-tracing
[dependencies-url]: https://david-dm.org/open-telemetry/opentelemetry-js?path=packages%2Fopentelemetry-tracing
[devDependencies-image]: https://david-dm.org/open-telemetry/opentelemetry-js/dev-status.svg?path=packages/opentelemetry-tracing
[devDependencies-url]: https://david-dm.org/open-telemetry/opentelemetry-js?path=packages%2Fopentelemetry-tracing&type=dev
[npm-url]: https://www.npmjs.com/package/@opentelemetry/tracing
[npm-img]: https://badge.fury.io/js/%40opentelemetry%2Ftracing.svg
