Camunda Workflow

An opinionated interface to Camunda for Ruby/Rails apps

Camunda Workflow uses Spyke to communicate with the Camunda REST API. It executes External Service Tasks using a Ruby class corresponding to each Camunda external task.

Camunda Integration with Ruby

The Camunda model process definition key is the module name of your implementation classes.

An external task is created with a Ruby class name for the id. And the process definition key should be set as the topic name.

Tasks are fetched, locked and then queued. We expect classes (ActiveJob) to implement each external task. So, according to the above screenshots, the poller and queuer will expect a class called SomeProcess::SomeTask to be implemented in your app.

Integration with your worker classes

Worker classes should inherit from CamundaJob. It is generated with rails g camunda:install.

perform is implemented on Camunda::ExternalTaskJob. It calls bpmn_perform with variables from Camunda and returns the results back to Camunda.

class CamundaJob < ApplicationJob
  # If using Sidekiq, change to include Sidekiq::Worker instead of inheriting from ApplicationJob
  include Camunda::ExternalTaskJob
end

class SomeProcess::SomeTask < CamundaJob
  def bpmn_perform(variables)
    do_something(variables[:foo])

    # A hash returned will become variables in the Camunda BPMN process instance
    { foo: 'bar', foo2: { json: "str" }, array_var: ["str"] }
  end
end

Exceptions create Camunda incidents

If your implementation throws an exception, it is caught and then sent to Camunda with a stack trace.

Supporting bpmn exceptions

Camunda supports throwing bpmn exceptions on a service task to communicate logic errors and not underlying code errors. These expected errors are thrown with

class SomeProcess::SomeTask < CamundaJob
  def bpmn_perform(variables)
    result = do_something(variables[:foo])

    if result == :expected
      { foo: 'bar', foo2: { json: "str" }, array_var: ["str"] }
    else
      raise Camunda::BpmnError.new error_code: 'bpmn-error', message: "Special BPMN error", variables: { bpmn: 'error' }
    end
  end
end

Generators

Java Spring Boot App install

rails generate camunda:spring_boot

Creates a skeleton Java Spring Boot app, which also contains the minimal files to run unit tests on a BPMN file. The Spring boot app can be used to start a Camunda instance with a REST api and also be deployed to PCF by generating a Spring Boot jar and pushing it.

BPMN ActiveJob install

rails generate camunda:install

Creates app/jobs/camunda_job.rb. A class that inherits from ApplicationJob and includes ExternalTaskJob. It can be changed to include Sidekiq::Worker instead.

All of the BPMN worker classes will inherit from this class

BPMN Classes

rails generate camunda:bpmn_classes

Parses the BPMN file and creates task classes according to the ID of the process file and the ID of each task. It checks each task and only creates it if the topic name is the same as the process ID. This allows one to have some tasks be handled outside the Rails app. It confirms that the ID's are valid Ruby constant names.

Starting the Camunda server for development

Java 7 and Apache Maven are requirements to run the Camunda server. We are using the Spring distribution. The Camunda application has a pom.xml, which Maven uses to install the required dependencies.

Start the application:

cd bpmn/java_app
mvn spring-boot:run

# Or use the included rake task:
# Start the Camunda spring boot app with `mvn spring-boot:run`
rake camunda:run

If you create Java based unit tests for your bpmn file they can be run with an included rake task as well.

Running java unit tests

cd bpmn/java_app
mvn clean test

# Or use the included rake task:
# Runs spring boot test suite with `mvn clean test`
rake camunda:test

Camunda-workflow defaults to an in-memory, h2 database engine. If you rather use a Postgres database engine, comment out the h2 database engine settings in the pom.xml file located in bpmn/java_app. Default settings for using Postgres are available in the pom.xml file. You will need to create a Postgres database on localhost called camunda.

Configuration

Engine Route Prefix of the Java Spring Boot app

The default engine route prefix for the provided Java Spring Boot app is rest. If you choose to download and use the Camunda distribution, the engine prefix is rest-engine. Camunda-workflow is configured to use rest by default.

To override the default engine route prefix, you need to add an initializer file in your rails app.

# filename initializers/camunda.rb
Camunda::Workflow.configure do |config|
  config.engine_route_prefix = 'rest-engine'
end

Enable HTTP Basic Auth for Java Spring Boot app

Authentication can be enabled in the Camunda Java Spring Boot app by setting an environment variable CAMUNDA_AUTH to true or false or by setting the camunda.authentication variable located in the application.properties (bpmn/java_app/src/main/resources) file to true.

When HTTP Basic Auth is enabled, it's required that a user with the appropriate permissions is setup in Camunda. Otherwise, the request will return as 401 unauthorized. Users are set up within the admin dashboard of Camunda and used to authenticate by passing an Authorization header during requests to the REST API. Below is how to configure the camunda_user and camunda_password to be used in the header request to authenticate using HTTP Basic Auth.

# filename initializers/camunda.rb
Camunda::Workflow.configure do |config|
  config.camunda_user = ENV['CAMUNDA_USER']
  config.camunda_password = ENV['CAMUNDA_PASSWORD']
end

Generating a jar for deployment

mvn package spring-boot:repackage

The jar is in target/camunda-bpm-springboot.jar

Deploying to PCF

cf push app_name -p target/camunda-bpm-springboot.jar

It will fail to start. Create a postgres database as a service in PCF and bind it to the application. The Springboot application is configured for Postgres and will then be able to start.

Usage

Add to your Gemfile

  gem 'camunda-workflow'

Deploying a model

Uses a default name, etc. Below outlines how to deploy a process using the included sample.bpmn file created by the generator. Alternatively you can deploy using Camunda Modeler

 Camunda::Deployment.create file_names: ['bpmn/diagrams/sample.bpmn']

Processes

Starting a process

  start_response = Camunda::ProcessDefinition.start_by_key'CamundaWorkflow', variables: { x: 'abcd' }, businessKey: 'WorkflowBusinessKey'

Camunda cannot handle snake case variables, all snake_case variables are serialized to camelCase before a request is sent to the REST api. Variables returned back from the Camunda API will be deserialized back to snake_case.

{ my_variable: "xyz" }

will be converted to:

{ myVariable: "xyz" }

Destroy a process

 Camunda::ProcessInstance.destroy_existing start_response.id

Tasks

Fetch tasks and queue with ActiveJob

The poller runs an infinite loop with long polling to fetch tasks, queue, and run them. The topic is the process definition key, as shown in the screenshot example from the Camunda Modeler.

Below will run the poller to fetch, lock, and run a task for the example process definition located in the starting a process detailed above.

Poller will need to run in a separate process or thread and needs to be running constantly in order to poll Camunda and queue jobs.

 Camunda::Poller.fetch_and_queue %w[CamundaWorkflow]

Running the poller in a separate thread

We have had success with running a long running thread in a Rails app using Rufus Scheduler. Something like:

rufus_scheduler.in('10.seconds') do
  Camunda::Poller.fetch_and_queue %w[Topics]
end

Fetch tasks For testing from the console

tasks = Camunda::ExternalTask.fetch_and_lock %w[CamundaWorkflow]

Run a task

tasks.each(&:run_now)

User Tasks

Mark a user task complete

 # Or you can query Camunda::Task with other parameters like assignee task.complete!(var1: 'value')
Camunda::Task.find_by_business_key_and_task_definition_key!(instance_business_key, task_key).complete!

Rspec Helpers

RSpec helpers validate your application to make sure it has a class for every External task in a given BPMN file.

require 'camunda/matchers'

RSpec.describe "BPMN Diagrams" do
  describe Camunda::BpmnXML.new(File.open("bpmn/diagrams/YourFile.bpmn")) do
    it { is_expected.to have_module('YourModule') }
    it { is_expected.to have_topics(%w[YourModule]) }
    it { is_expected.to have_defined_classes }
  end
end

Contributing

See CONTRIBUTING for additional information.

Public domain

This project is in the worldwide public domain. As stated in CONTRIBUTING:

This project is in the public domain within the United States, and copyright and related rights in the work worldwide are waived through the CC0 1.0 Universal public domain dedication.

All contributions to this project will be released under the CC0 dedication. By submitting a pull request, you are agreeing to comply with this waiver of copyright interest.