# OpenTelemetry instrumentation for bunyan

[![NPM Published Version][npm-img]][npm-url]
[![Apache License][license-image]][license-image]

This module provides automatic instrumentation of the [`bunyan`](https://www.npmjs.com/package/bunyan) module to inject trace-context into Bunyan log records (log correlation) and to send Bunyan logging to the OpenTelemetry Logging SDK (log sending).

If total installation size is not constrained, it is recommended to use the [`@opentelemetry/auto-instrumentations-node`](https://www.npmjs.com/package/@opentelemetry/auto-instrumentations-node) bundle with [@opentelemetry/sdk-node](`https://www.npmjs.com/package/@opentelemetry/sdk-node`) for the most seamless instrumentation experience.

Compatible with OpenTelemetry JS API and SDK `1.0+`.

## Installation

```bash
npm install --save @opentelemetry/instrumentation-bunyan
```

## Supported Versions

- [`bunyan`](https://www.npmjs.com/package/bunyan) versions `>=1.0.0 <2`

## Usage

```js
const { trace } = require('@opentelemetry/api');
const { SimpleSpanProcessor, ConsoleSpanExporter } = require('@opentelemetry/sdk-trace');
const { SimpleLogRecordProcessor, ConsoleLogRecordExporter } = require('@opentelemetry/sdk-logs');
const { NodeSDK } = require('@opentelemetry/sdk-node');
const { BunyanInstrumentation } = require('@opentelemetry/instrumentation-bunyan');

const sdk = new NodeSDK({
  spanProcessors: [
    new SimpleSpanProcessor(new ConsoleSpanExporter()),
  ],
  logRecordProcessors: [
    new SimpleLogRecordProcessor({ exporter: new ConsoleLogRecordExporter() }),
  ],
  instrumentations: [
    new BunyanInstrumentation({
      // See below for Bunyan instrumentation options.
    }),
  ]
});
sdk.start();
process.once('beforeExit', async () => { await sdk.shutdown(); });

const bunyan = require('bunyan');
const logger = bunyan.createLogger({name: 'example'});

logger.info('hi');
// 1. Log records will be sent to the SDK-registered log record processor, if any.
//    This is called "log sending".

const tracer = trace.getTracer('example');
tracer.startActiveSpan('manual-span', span => {
  logger.info('in a span');
  // 2. Fields identifying the current span will be added to log records:
  //    {"name":"example",...,"msg":"in a span","trace_id":"d61b4e4af1032e0aae279d12f3ab0159","span_id":"d140da862204f2a2","trace_flags":"01"}
  //    This is called "log correlation".
})
```

### Log sending

Creation of a Bunyan Logger will automatically add a [Bunyan stream](https://github.com/trentm/node-bunyan#streams) that sends log records to the OpenTelemetry Logs SDK. The OpenTelemetry SDK can be configured to handle those records -- for example, sending them on to an OpenTelemetry collector for log archiving and processing. The example above shows a minimal configuration that emits OpenTelemetry log records to the console for debugging.

If the OpenTelemetry SDK is not configured with a Logger provider, then this added stream will be a no-op.

Log sending can be disabled with the `disableLogSending: true` option.

When Bunyan emits a top-level `err` field, for example via
`logger.error(err, 'msg')`, this instrumentation forwards it through the Logs
API `exception` field so the SDK can populate standard `exception.*`
attributes.

### Log correlation

Bunyan logger calls in the context of a tracing span will have fields
identifying the span added to the log record. This allows
[correlating](https://opentelemetry.io/docs/specs/otel/logs/#log-correlation)
log records with tracing data. The added fields are
([spec](https://opentelemetry.io/docs/specs/otel/compatibility/logging_trace_context/)):

- `trace_id`
- `span_id`
- `trace_flags`

After adding these fields, the optional `logHook` is called to allow injecting additional fields. For example:

```js
  logHook: (span, record) => {
    record['resource.service.name'] = provider.resource.attributes['service.name'];
  }
```

When no span context is active or the span context is invalid, injection is skipped.
Log injection can be disabled with the `disableLogCorrelation: true` option.

### Bunyan instrumentation options

| Option                  | Type              | Description                                                                                                                                                |
|-------------------------|-------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------|
| `disableLogSending`     | `boolean`         | Whether to disable [log sending](#log-sending). Default `false`.                                                                                           |
| `logSeverity`           | `SeverityNumber`  | Control severity level for [log sending](#log-sending). Default `SeverityNumber.UNSPECIFIED`, it will use Bunnyan Logger's current level when unspecified. |
| `disableLogCorrelation` | `boolean`         | Whether to disable [log correlation](#log-correlation). Default `false`.                                                                                   |
| `logHook`               | `LogHookFunction` | An option hook to inject additional context to a log record after trace-context has been added. This requires `disableLogCorrelation` to be false.         |

### Using OpenTelemetryBunyanStream without instrumentation

This package exports the Bunyan stream class that is used to send records to the
OpenTelemetry Logs SDK. It can be used directly when configuring a Bunyan logger
if one is not using the `BunyanInstrumentation` for whatever reason. For
example:

```js
const { OpenTelemetryBunyanStream } = require('@opentelemetry/instrumentation-bunyan');
const bunyan = require('bunyan');

// You must register an OpenTelemetry LoggerProvider, otherwise log records will
// be sent to a no-op implementation. "examples/telemetry.js" shows one way
// to configure one.
// ...

const logger = bunyan.createLogger({
  name: 'my-logger',
  streams: [
    {
      type: 'raw',
      stream: new OpenTelemetryBunyanStream()
    }
  ],
});
```

## Semantic Conventions

This package forwards Bunyan `err` fields through the Logs API `exception`
field, allowing the SDK to populate standard `exception.*` attributes.

## 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 in [GitHub Discussions][discussions-url]

## License

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

[discussions-url]: https://github.com/open-telemetry/opentelemetry-js/discussions
[license-url]: https://github.com/open-telemetry/opentelemetry-js-contrib/blob/main/LICENSE
[license-image]: https://img.shields.io/badge/license-Apache_2.0-green.svg?style=flat
[npm-url]: https://www.npmjs.com/package/@opentelemetry/instrumentation-bunyan
[npm-img]: https://badge.fury.io/js/%40opentelemetry%2Finstrumentation-bunyan.svg
