npm package: @p.r/jaeger-client
Description: Jaeger binding for OpenTracing Node
Author: Onwukike Ibe
Latest version: 3.18.0

[![Build Status][ci-img]][ci] [![Coverage Status][cov-img]][cov] [![NPM Published Version][npm-img]][npm] [![OpenTracing 1.0 Enabled][ot-img]][ot-url]

# Jaeger Bindings for Javascript OpenTracing API

This is [Jaeger](https://jaegertracing.io/)'s client side instrumentation library for Node.js that implements [Javascript OpenTracing API 1.0](https://github.com/opentracing/opentracing-javascript/).

## Contributing and Developing

Please see [CONTRIBUTING.md](./CONTRIBUTING.md).

## Installation

`npm install --save jaeger-client`

## Initialization

The Tracer defaults to sending spans over UDP to the jaeger-agent running on localhost; the jaeger-agent handles forwarding the spans to the jaeger-collector. When you are instantiating your client instance you can specify the sampler of your choice. The library support the following samplers:

| SAMPLER       | KEY             |
| ------------- | --------------- |
| Constant      | `const`         |
| Probabilistic | `probabilistic` |
| Rate Limiting | `ratelimiting`  |
| Remote        | `remote`        |

More information about sampling can be found [here](https://www.jaegertracing.io/docs/1.7/sampling/#client-sampling-configuration)

```javascript
var initTracer = require('jaeger-client').initTracer;

// See schema https://github.com/jaegertracing/jaeger-client-node/blob/master/src/configuration.js#L37
var config = {
  serviceName: 'my-awesome-service',
};
var options = {
  tags: {
    'my-awesome-service.version': '1.1.2',
  },
  metrics: metrics,
  logger: logger,
};
var tracer = initTracer(config, options);
```

### Environment variables

The tracer can be initialized with values coming from environment variables:

```jhavascript:
var tracer = initTracerFromEnv(config, options);
```

None of the env vars are required and all of them can be overridden via properties on the `config` object.

| Property                         | Description                                                                                                                                                                                                                                                                                                      |
| -------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| JAEGER_SERVICE_NAME              | The service name                                                                                                                                                                                                                                                                                                 |
| JAEGER_AGENT_HOST                | The hostname for communicating with agent via UDP                                                                                                                                                                                                                                                                |
| JAEGER_AGENT_PORT                | The port for communicating with agent via UDP                                                                                                                                                                                                                                                                    |
| JAEGER_ENDPOINT                  | The HTTP endpoint for sending spans directly to a collector, i.e. http://jaeger-collector:14268/api/traces                                                                                                                                                                                                       |
| JAEGER_USER                      | Username to send as part of "Basic" authentication to the collector endpoint                                                                                                                                                                                                                                     |
| JAEGER_PASSWORD                  | Password to send as part of "Basic" authentication to the collector endpoint                                                                                                                                                                                                                                     |
| JAEGER_REPORTER_LOG_SPANS        | Whether the reporter should also log the spans                                                                                                                                                                                                                                                                   |
| JAEGER_REPORTER_FLUSH_INTERVAL   | The reporter's flush interval (ms)                                                                                                                                                                                                                                                                               |
| JAEGER_SAMPLER_TYPE              | The sampler type                                                                                                                                                                                                                                                                                                 |
| JAEGER_SAMPLER_PARAM             | The sampler parameter (number)                                                                                                                                                                                                                                                                                   |
| JAEGER_SAMPLER_MANAGER_HOST_PORT | The HTTP endpoint when using the remote sampler, i.e. http://jaeger-agent:5778/sampling                                                                                                                                                                                                                          |
| JAEGER_SAMPLER_REFRESH_INTERVAL  | How often the remotely controlled sampler will poll jaeger-agent for the appropriate sampling strategy                                                                                                                                                                                                           |
| JAEGER_TAGS                      | A comma separated list of `name = value` tracer level tags, which get added to all reported spans. The value can also refer to an environment variable using the format `${envVarName:default}`, where the `:default` is optional, and identifies a value to be used if the environment variable cannot be found |
| JAEGER_DISABLED                  | Whether the tracer is disabled or not. If true, the default `opentracing.NoopTracer` is used.                                                                                                                                                                                                                    |

By default, the client sends traces via UDP to the agent at `localhost:6832`. Use `JAEGER_AGENT_HOST` and `JAEGER_AGENT_PORT` to send UDP traces to a different `host:port`. If `JAEGER_ENDPOINT` is set, the client sends traces to the endpoint via `HTTP`, making the `JAEGER_AGENT_HOST` and `JAEGER_AGENT_PORT` unused. If `JAEGER_ENDPOINT` is secured, HTTP basic authentication can be performed by setting the `JAEGER_USER` and `JAEGER_PASSWORD` environment variables.

#### Reporting spans via HTTP

UDP has a hard size limit of 65,507 bytes; if the span is larger than this limit, the tracer will drop the span. To circumvent this, you can configure the tracer to directly send spans to the jaeger-collector over HTTP (skipping the jaeger-agent altogether).

```javascript
var initTracer = require('jaeger-client').initTracer;

// See schema https://github.com/jaegertracing/jaeger-client-node/blob/master/src/configuration.js#L37
var config = {
  serviceName: 'my-awesome-service',
  reporter: {
    // Provide the traces endpoint; this forces the client to connect directly to the Collector and send
    // spans over HTTP
    collectorEndpoint: 'http://jaeger-collector:14268/api/traces',
    // Provide username and password if authentication is enabled in the Collector
    // username: '',
    // password: '',
  },
};
var options = {
  tags: {
    'my-awesome-service.version': '1.1.2',
  },
  metrics: metrics,
  logger: logger,
};
var tracer = initTracer(config, options);
```

### Metrics and Logging

The `metrics` and `logger` objects shown in the above example must satisfy the [MetricsFactory](./src/_flow/metrics.js#L34) and [Logger](./src/_flow/logger.js) APIs respectively.

#### Prometheus metrics

This module brings a [Prometheus(prom-client)](https://www.npmjs.com/package/prom-client) integration to the internal Jaeger metrics.  
The way to initialize the tracer with Prometheus metrics:

```javascript
var PrometheusMetricsFactory = require('jaeger-client').PrometheusMetricsFactory;
var promClient = require('prom-client');

var config = {
  serviceName: 'my-awesome-service',
};
var namespace = config.serviceName;
var metrics = new PrometheusMetricsFactory(promClient, namespace);
var options = {
  metrics: metrics,
};
var tracer = initTracer(config, options);
```

## Usage

The Tracer instance created by `initTracer` is OpenTracing-1.0 compliant. See [opentracing-javascript](https://github.com/opentracing/opentracing-javascript) for usage examples.

### TChannel Span Bridging

Because [tchannel-node](https://github.com/uber/tchannel-node) does not have instrumentation for OpenTracing, Jaeger-Client exposes methods wrapping tchannel handlers, and encoded channels. An encoded channel is a channel wrapped in either a thrift encoder `TChannelAsThrift`, or json encoder `TChannelAsJson`. To wrap a server handler for thrift one can initialize a tchannel bridge, and wrap the encoded handler function with a `tracedHandler` decorator. The tchannel bridge takes an OpenTracing tracer, and a context factory. The context factory must be a function that returns a context with the methods 'getSpan', and 'setSpan' which retrieve and assign the span to the context respectively.

```javascript
import { TChannelBridge } from 'jaeger-client';
import Context from 'some-conformant-context';

function contextFactory() {
  return new Context();
}

let bridge = new TChannelBridge(tracer, { contextFactory: contextFactory });
let server = new TChannel({ serviceName: 'server' });
server.listen(4040, '127.0.0.1');
let serverThriftChannel = TChannelAsThrift({
  channel: server,
  entryPoint: path.join(__dirname, 'thrift', 'echo.thrift'), // file path to a thrift file
});

let perProcessOptions = {};
serverThriftChannel.register(
  server,
  'Echo::echo',
  perProcessOptions,
  bridge.tracedHandler((perProcessOptions, req, head, body, callback) => {
    /* Your handler code goes here. */
  })
);
```

Outbound calls can be made in two ways, shown below.

#### Using encoded channel to create a request and calling `request.send()`

```javascript
import { TChannelBridge } from 'jaeger-client';

let bridge = new TChannelBridge(tracer);
// Create the toplevel client channel.
let client = new TChannel();

// Create the client subchannel that makes requests.
let clientSubChannel = client.makeSubChannel({
  serviceName: 'server',
  peers: ['127.0.0.1:4040'],
});

let encodedThriftChannel = TChannelAsThrift({
  channel: clientSubChannel,
  entryPoint: path.join(__dirname, 'thrift', 'echo.thrift'), // file path to a thrift file
});

// wrap encodedThriftChannel in a tracing decorator
let tracedChannel = bridge.tracedChannel(encodedThriftChannel);

// The encodedThriftChannel's (also true for json encoded channels) request object can call 'send' directly.
let req = tracedChannel.request({
  serviceName: 'server',
  context: context, // must be passed through from the service handler shown above
  headers: { cn: 'echo' },
});

// headers should contain your outgoing tchannel headers if any.
// In this instance 'send' is being called on the request object, and not the channel.
req.send('Echo::echo', headers, { value: 'some-string' });
```

#### Using top level channel to create a request and calling `encodedChannel.send(request)`

```javascript
let tracedChannel = bridge.tracedChannel(encodedThriftChannel);

// tracedChannel.channel refers to encodedThriftChannel's inner channel which
// is clientSubChannel in this instance.
let req = tracedChannel.channel.request({
  serviceName: 'server',
  headers: { cn: 'echo' },
  context: context, // must be passed through from the service handler shown above
  timeout: someTimeout,
});
// send() can be called directly on the tracing decorator
tracedChannel.send(req, 'Echo::echo', o.headers, { value: 'some-string' }, clientCallback);
```

### Debug Traces (Forced Sampling)

#### Programmatically

The OpenTracing API defines a `sampling.priority` standard tag that can be used to affect the sampling of a span and its children:

```javascript
span.setTag(opentracing_tags.SAMPLING_PRIORITY, 1);
```

#### Via HTTP Headers

Jaeger Tracer also understands a special HTTP Header `jaeger-debug-id`, which can be set in the incoming request, e.g.

```sh
curl -H "jaeger-debug-id: some-correlation-id" http://myhost.com
```

When Jaeger sees this header in the request that otherwise has no tracing context, it ensures that the new trace started for this request will be sampled in the "debug" mode (meaning it should survive all downsampling that might happen in the collection pipeline), and the root span will have a tag as if this statement was executed:

```javascript
span.setTag('jaeger-debug-id', 'some-correlation-id');
```

This allows using Jaeger UI to find the trace by this tag.

### Zipkin Compatibility

Support for [Zipkin's B3 Propagation HTTP headers](https://github.com/openzipkin/b3-propagation) is provided by the `ZipkinB3TextMapCodec`, which can be configured instead of the default `TextMapCodec`.

The new codec can be used by registering it with a tracer instance as both an injector and an extractor:

```
let codec = new ZipkinB3TextMapCodec({ urlEncoding: true });

tracer.registerInjector(opentracing.FORMAT_HTTP_HEADERS, codec);
tracer.registerExtractor(opentracing.FORMAT_HTTP_HEADERS, codec);
```

This can prove useful when compatibility with existing Zipkin tracing/instrumentation is desired.

## License

[Apache 2.0 License](./LICENSE).

[ci-img]: https://travis-ci.org/jaegertracing/jaeger-client-node.svg?branch=master
[ci]: https://travis-ci.org/jaegertracing/jaeger-client-node
[cov-img]: https://codecov.io/gh/jaegertracing/jaeger-client-node/branch/master/graph/badge.svg
[cov]: https://codecov.io/gh/jaegertracing/jaeger-client-node/branch/master/
[npm-img]: https://badge.fury.io/js/jaeger-client.svg
[npm]: https://www.npmjs.com/package/jaeger-client
[ot-img]: https://img.shields.io/badge/OpenTracing--1.0-enabled-blue.svg
[ot-url]: http://opentracing.io