ctrace-js

Canonical OpenTracing for Javascript

Currently this only supports Node.js usage. Browser-based Javascript support will be added later.

Why

OpenTracing is a young specification and for most (if not all) SDK implementations, output format and wire protocol are specific to the backend platform implementation. ctrace-js attempts to decouple the format and wire protocol from the backend tracer implementation.

What

ctrace-js specifies a canonical format for trace logs. By default the logs are output to stdout but you can configure them to go to any WritableStream.

Required Reading

To fully understand this platform API, it's helpful to be familiar with the OpenTracing project project, terminology, and ctrace-js specification more specifically.

Install

Install via npm as follows:

$ npm install ctrace-js --save

Usage

Add instrumentation to the operations you want to track. This is composed primarily of using "spans" around operations of interest and adding log statements to capture useful data relevant to those operations.

Initialize Global Tracer

First, initialize the global tracer as follows.

const tracer = require('ctrace-js')

OR, initialize the global tracer with custom options as follows.

const tracer = require('ctrace-js')
tracer.init({
  multiEvent: true,  // true for Multi-Event Mode; false for Single-Event Mode.  defaults to false.
  debug: true,       // true to enabling debugging.  defaults to false.
  propagators: {     // custom propagators mapped to format type
    [tracer.FORMAT_HTTP_HEADERS]: [
      {
        extract: (carrier) => {
          if (carrier['x-correlation-id']) {
            return {
              traceId: carrier['x-correlation-id'],
              spanId: carrier['x-correlation-id']
            }
          }
        }
      }
    ]
  },
  stream: { // optional but defaults to stdout
    write: (content) => { // Modify the anonymous function to write logs to an writable stream
      console.log(content)
    }
  },
  serviceName: "ExampleService" // can set service name for entire tracer
})

Client HTTP Requests

To trace client HTTP requests you can use the request wrapper for request-promise or request. To trace a request using request-promise do the following.

const request = require('ctrace-js').request

OR, to trace using request do the following.

const request = require('ctrace-js').request
request.init(require('request'))

You can then send HTTP(S) requests in this or other modules as follows.

const request = require('ctrace-js').request

function send (span, uri, body) {
  return request({
    method: 'POST',
    uri: uri,
    body: body,
    traceContext: {
      span: span   // Current opentracing span
    }
  })
}

Use Express Middleware for server spans

Add the Express Middleware as follows to trace HTTP REST server calls.

const express = require('express')
const tracer = require('ctrace-js')
const app = express()

app.use(tracer.express())

app.post('/users', (req, res) => {
  // ...
})

Log Event

Log events as follows.

app.post('/users', (req, res) => {
  const span = req.span
  span.log({event: 'SaveUser', userId: 'u123'})
  // ...
})

Log Errors

Log errors and return visible trace context as follows.

app.post('/users', (req, res) => {
  const span = req.span
  try {
    // ...
  } catch (err) {
    span.log({
      event: 'error',
      'error.kind': 'Exception',
      message: err.message,
      stack: err.stack
    })

    let ctx = span.context()
    res.status(500).json({
      error: err.message,
      traceId: ctx.traceId,
      spanId: ctx.spanId
    })
  }
})

[Advanced Usage]

The following are examples of advanced usage. In these examples, tracing is done manually rather than using auto-instrumentation middleware.

NOTE: If you are using auto-instrumentation middleware (express, request, etc) there is no need to use manually start and finish spans.

Start Client Span

If you want to track a call to a downstream REST service, start a new client Span like this.

const span = tracer.startSpan('RegisterUser', {
  // Apply Standard Tags
  tags: {
    'span.kind': 'client',
    'component': 'UserAdapter',
    'peer.hostname': 'my-registry.net',
    'peer.port': '443',
    'peer.service': 'UserRegistry',
    'http.method': 'POST',
    'http.url': 'https://my-registry.net/users?apikey=293283209'
  }
})

Inject Context

The downstream REST service will want to use this span as its parent. We will inject the span context into the HTTP Headers for this purpose as follows.

const headers = {}
tracer.inject(span.context(), Tracer.FORMAT_HTTP_HEADERS, headers)

Start Server Span

The called REST service can start a server Span as follows.

const express = require('express')
const app = express()
const tracer = require('ctrace')

app.post('/users', (req, res) => {
  const context = tracer.extract(tracer.FORMAT_HTTP_HEADERS, req.headers)
  const span = tracer.startSpan('RegisterUser', {
    childOf: context,  // include parent context
    // Standard Tags
    tags: {
      'span.kind': 'server',
      'component': 'UserRegistryController',
      'peer.ipv4': req.ip,
      'http.method': req.method,
      'http.url': req.url
    }
  })

  ...

})

Finish Server Span

If the REST service call completes successfully on the server, add tag for status and finish the span.

app.post('/users', (req, res) => {

  ...

  span.addTags({'http.status_code': 200})
  span.finish()
  res.status(200).json(result)
})

If it completes with an error, , do the following to add tags for status code, error=true, recommended error_details, and finish the span.

app.post('/users', (req, res) => {

  ...

  span.addTags({
    'http.status_code': 500,
    'error': true,
    'error_details': error.toString()
  })
  span.finish()
  res.status(500).json(error)
})

Finish Client Span

If the call to the downstream REST service completes successfully, finish the client Span like this.

span.addTags({'http.status_code': 200})
span.finish()

If the call completes with an error, finish the client Span like this.

span.addTags({
  // Standard Tags and Recommended error_details
  'http.status_code': 500,
  'error': true,
  'error_details': err.toString()
})
span.finish()

API

SpanContext

An object containing the context used to propagate from span to span

Type: object

Properties

• traceId string id of trace including multiple spans
• spanId string id of span (start/stop event)
• baggage Object<string, string> optional key/value map of tags that carry across spans in a single trace.

Propagators

Type: Array<Propagator>

GlobalTracer

Global tracer singleton. This is accessed as follows.

const tracer = require('ctrace')

startSpan

Singleton wrapper for Tracer#startSpan

Parameters

• name
• context

init

Used to initialize global tracer singleton

Parameters

• options object options used to initialize tracer
  • options.multiEvent bool? true for multi-event mode; otherwise, single-event mode
  • options.debug bool? true for debug; otherwise, it is disabled
  • options.propagators Object<string, Propagators>? optional propagators
  • options.serviceName string? allows the configuration of the "service" tag for the entire Tracer if not specified here, can also be set using env variable "ctrace_service_name"

Propagator

Interface for custom context propagation. If extract or inject methods are present they will be used in the propagation chain.

extract

Extract span context from a given carrier.

Parameters

• carrier object

Returns SpanContext

inject

Inject span context into a given carrier.

Parameters

• spanContext SpanContext
• carrier object

Span

Extends opentracing.Span

Span represents a logical unit of work as part of a broader Trace. Examples of span might include remote procedure calls or a in-process function calls to sub-components. A Trace has a single, top-level "root" Span that in turn may have zero or more child Spans, which in turn may have children.

Parameters

• tracer
• fields

constructor

Constructor for internal use only. To start a span call Tracer#startSpan

Parameters

• tracer Tracer
• fields object

context

Returns the SpanContext object associated with this Span.

Returns SpanContext

tracer

Returns the Tracer object used to create this Span.

Returns Tracer

setOperationName

Sets the string name for the logical operation this span represents.

Parameters

• name string

Returns Span this

setBaggageItem

Sets a key:value pair on this Span that also propagates to future children of the associated Span.

setBaggageItem() enables powerful functionality given a full-stack opentracing integration (e.g., arbitrary application data from a web client can make it, transparently, all the way into the depths of a storage system), and with it some powerful costs: use this feature with care.

IMPORTANT NOTE #1: setBaggageItem() will only propagate baggage items to future causal descendants of the associated Span.

IMPORTANT NOTE #2: Use this thoughtfully and with care. Every key and value is copied into every local and remote child of the associated Span, and that can add up to a lot of network and cpu overhead.

Parameters

• key string
• value string

getBaggageItem

Returns the value for a baggage item given its key.

Parameters

• key string The key for the given trace attribute.

Returns string String value for the given key, or undefined if the key does not correspond to a set trace attribute.

setTag

Adds a single tag to the span. See addTags() for details.

Parameters

• key string
• value object

Returns Span this

addTags

Adds the given key value pairs to the set of span tags.

Multiple calls to addTags() results in the tags being the superset of all calls.

The behavior of setting the same key multiple times on the same span is undefined.

The supported type of the values is implementation-dependent. Implementations are expected to safely handle all types of values but may choose to ignore unrecognized / unhandle-able values (e.g. objects with cyclic references, function objects).

Parameters

• keyValues object<string, object>

Returns Span this

log

Add a log record to this Span, optionally at a user-provided timestamp.

For example:

span.log({
    size: rpc.size(),  // numeric value
    URI: rpc.URI(),  // string value
    payload: rpc.payload(),  // Object value
    "keys can be arbitrary strings": rpc.foo(),
});

span.log({
    "error.description": someError.description(),
}, someError.timestampMillis());

Parameters

• keyValues object<string, object> An object mapping string keys to arbitrary value types. All Tracer implementations should support bool, string, and numeric value types, and some may also support Object values.
• timestamp number An optional parameter specifying the timestamp in milliseconds since the Unix epoch. Fractional values are allowed so that timestamps with sub-millisecond accuracy can be represented. If not specified, the implementation is expected to use its notion of the current time of the call.

Returns Span this

finish

Sets the end timestamp and finalizes Span state.

With the exception of calls to Span.context() (which are always allowed), finish() must be the last call made to any span instance, and to do otherwise leads to undefined behavior.

Parameters

• finishTime number Optional finish time in milliseconds as a Unix timestamp. Decimal values are supported for timestamps with sub-millisecond accuracy. If not specified, the current time (as defined by the implementation) will be used.

Tracer

Tracer is the tracing entry-point. It facilitates starting a new span and context propagation (ie. inject, extract).

Parameters

• options (optional, default {})
  • options.redactList array<string, RegExp>? optional list of keys, when matched, replaces values with ***
  • options.ignoreRoutes array<string>? optional list of routes to ignore. These routes will not generate a trace in the logs. Routes can be of the format GET:/route, or the less specific /route, which will ignore any HTTP method call to that route.

constructor

Construct a new tracer for internal use only. Use GlobalTracer#init to set global trace options.

Parameters

• options object options used to initialize tracer (optional, default {})
  • options.multiEvent bool? true for multi-event mode; otherwise, single-event mode
  • options.debug bool? true for debug; otherwise, it is disabled
  • options.propagators object<string, Propagators>? optional propagators
  • options.serviceName string? allows the configuration of the "service" tag for the entire Tracer if not specified here, can also be set using env variable "ctrace_service_name"

startSpan

Starts and returns a new Span representing a logical unit of work.

For example:

// Start a new (parentless) root Span:
let parent = tracer.startSpan('DoWork')

// Start a new (child) Span:
let child = tracer.startSpan('Subroutine', {
    childOf: parent,
});

Parameters

• name string the name of the operation.
• options object? the fields to set on the newly created span. (optional, default {})
  • options.childOf (Span | SpanContext)? a parent SpanContext (or Span, for convenience) that the newly-started span will be the child of (per REFERENCE_CHILD_OF). If specified, fields.references must be unspecified.
  • options.tags object<string, object>? set of key-value pairs which will be set as tags on the newly created Span. Ownership of the object is passed to the created span for efficiency reasons (the caller should not modify this object after calling startSpan).

Returns Span a new Span object.

inject

Injects the given SpanContext instance for cross-process propagation within carrier. The expected type of carrier depends on the value of `format.

OpenTracing defines a common set of format values (see FORMAT_TEXT_MAP, FORMAT_HTTP_HEADERS, and FORMAT_BINARY), and each has an expected carrier type.

Consider this pseudocode example:

var clientSpan = ...;
...
// Inject clientSpan into a text carrier.
var headersCarrier = {};
Tracer.inject(clientSpan.context(), Tracer.FORMAT_HTTP_HEADERS, headersCarrier);
// Incorporate the textCarrier into the outbound HTTP request header
// map.
Object.assign(outboundHTTPReq.headers, headersCarrier);
// ... send the httpReq

Parameters

• spanContext SpanContext the SpanContext to inject into the carrier object. As a convenience, a Span instance may be passed in instead (in which case its .context() is used for the inject()).
• format string the format of the carrier.
• carrier object see the documentation for the chosen format for a description of the carrier object.

extract

Returns a SpanContext instance extracted from carrier in the given format.

OpenTracing defines a common set of format values (see FORMAT_TEXT_MAP, FORMAT_HTTP_HEADERS, and FORMAT_BINARY), and each has an expected carrier type.

Consider this pseudocode example:

// Use the inbound HTTP request's headers as a text map carrier.
var headersCarrier = inboundHTTPReq.headers;
var wireCtx = Tracer.extract(Tracer.FORMAT_HTTP_HEADERS, headersCarrier);
var serverSpan = Tracer.startSpan('...', { childOf : wireCtx });

Parameters

• format string the format of the carrier.
• carrier object the type of the carrier object is determined by the format.

Returns SpanContext The extracted SpanContext, or undefined if no such SpanContext could be found in carrier

Roadmap

• Core Start, Log, and Finish Span
• Inject, Extract to Text and Header formats
• Inject, Extract to Binary format
• Express Middleware support
• Request and Request-Promise interceptor support
• Kinesis, Lambda and Plain Lambda wrapper support
• API Gateway / Lambda in Proxy Mode support