camunda-worker-node

Implement your external task workers for Camunda in NodeJS.

Compatible with Camunda >= 7.8. Requires NodeJS >= 6.0.

Usage

This library exposes a simple API to implement external task workers for Camunda.

var Worker = require('camunda-worker-node');
var Backoff = require('camunda-worker-node/lib/backoff');

var engineEndpoint = 'http://localhost:8080/engine-rest';

var worker = Worker(engineEndpoint, {
  workerId: 'some-worker-id',
  use: [
    Backoff
  ]
});

// a work subscription may access and modify process variables
worker.subscribe('work:A', [ 'numberVar' ], async function(context) {

  var newNumber = context.variables.numberVar + 1;

  // fail with an error if things go awry
  if (ooops) {
    throw new Error('no work done');
  }

  // complete with update variables
  return Complete({
    variables: {
      numberVar: newNumber
    }
  });
});

// stop the worker instance with the application
worker.stop();

Make sure you properly configured the external tasks in your BPMN 2.0 diagram:

<bpmn:serviceTask
  id="Task_A"
  camunda:type="external"
  camunda:topicName="work:A" />

Features

• Subscribe to work node-style or via async functions
• Complete tasks with updated variables or fail with errors
• Trigger BPMN errors
• Configure and extend task locks
• Configure logging and authentication
• Configure task fetching
• Control the worker life-cycle
• Extend via plug-ins

Resources

• Example
• Issues
• Changelog

Implementing Worker

Implement your workers via async, promise returning functions or pass results via node-style callbacks.

Work, Node Style

Use the provided callback to pass task execution errors and data, node-style:

// report work results via a node-style callback
workes.subscribe('work:B', function(context, callback) {

  var newNumber = context.variables.numberVar + 1;

  // indicate an error
  callback(
    new Error('no work done');
  );

  // or return actual result
  callback(null, {
    variables: {
      numberVar: newNumber
    }
  });
});

Work with async Function

ES6 style async/await to implement work is fully supported:

// implement work via a Promise returning async function
worker.subscribe('work:B', async function(context) {

  // await async increment
  var newNumber = await increment(context.variables.numberVar);

  // indicate an error
  throw new Error('no work done');

  // or return actual result
  return {
    variables: {
      numberVar: newNumber
    }
  };
});

Trigger BPMN Errors

You may indicate BPMN errors to trigger business defined exception handling:

worker.subscribe('work:B', async function(context) {

  // trigger business aka BPMN errors
  return {
    errorCode: 'some-bpmn-error'
  };
});

Task Locks

You may configure the initial lock time (defaults to 10 seconds) on worker registration.

At the same time you may use the method extendLock, provided via the task context, to increase the lock time while the worker is busy.

// configure three seconds as initial lock time
worker.subscribe('work:B', {
  lockDuration: 3000,
  variables: [ 'a' ]
}, async function(context) {

  var extendLock = context.extendLock;

  // extend the lock for another five seconds
  await extendLock(5000);

  // complete task
  return {};
});

Read more about external task locking in the Camunda Documentation.

Authentication

We provide middlewares for basic auth as well as token based authentication.

Basic Auth

Provide your client credentials via the BasicAuth middleware:

var worker = Worker(engineEndpoint, {
  use: [
    BasicAuth('walt', 'SECRET_PASSWORD')
  ]
};

Token Authentication

Provide your tokens via the Auth middleware:

var worker = Worker(engineEndpoint, {
  use: [
    Auth('Bearer', 'BEARER_TOKEN')
  ]
};

Custom Made

To support custom authentication options add additional request headers to authenticate your task worker via the requestOptions configuration:

var worker = Worker(engineEndpoint, {
  requestOptions: {
    headers: {
      Hello: 'Authenticated?'
    }
  }
})

Logging

We employ debug for logging.

Use the Logger extension in combination with DEBUG=* to capture a full trace of what's going on under the hood:

DEBUG=* node start-workers.js

Task Fetching

Task fetching is controlled by two configuration properties:

• maxTasks - maximum number of tasks to be fetched and locked with a single poll
• pollingInterval - interval in milliseconds between polls

You may configure both properties on worker creation and at run-time:

var worker = Worker(engineEndpoint, {
  maxTasks: 2,
  pollingInterval: 1500
});

// dynamically increase max tasks
worker.configure({
  maxTasks: 5
});

This way you can configure the task fetching behavior both statically and dynamically.

Roll your own middleware to dynamically configure the worker instance or let the Backoff middleware take care of it.

As an alternative to configuring these values you may stop and re-start the Worker instance as needed, too.

Worker Life-Cycle

Per default the worker instance will start to poll for work immediately. Configure this behavior via the autoPoll option and start, stop and re-start the instance programatically if you need to:

var worker = Worker(engineEndpoint, {
  autoPoll: false
});

// manually start polling
worker.start();

// stop later on
await worker.stop();

// re-start at some point in time
worker.start();

Extend via Plug-ins

A worker may be extended via the use config parameter.

Worker(engineEndpoint, {
  use: [
    Logger,
    Backoff,
    Metrics,
    BasicAuth('Walt', 'SECRET_PASSWORD')
  ]
});

Existing Extensions

• Logger - adds verbose logging of what is going on
• Backoff - dynamically adjust poll times based on Camunda REST api availability, fetched tasks and poll processing times
• Metrics - collect and periodically log utilization metrics
• BasicAuth - authorize against REST api with username + password
• Auth - authorize against REST api with arbitrary tokens

Dynamically Unregister a Work Subscription

It is possible to dynamically unregister a work subscription any time.

var subscription = worker.subscribe('someTopic', async function(context) {
  // do work
  console.log('doing work!');
});

// later
subscription.remove();

Installation

npm i --save camunda-worker-node

Develop

Install dependencies:

npm install

Lint and run all tests:

DEBUG=worker* npm run all

Note: You need a Camunda BPM REST API exposed on localhost:8080/engine-rest for the tests to pass. An easy way to get it up running is via Docker.

Related

• External task documentation
• Official external task client

License

MIT