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Camunda Workflow

An opinionated interface to Camunda for Ruby/Rails apps

Her is used to communicate with the Camunda REST API.

Add to your Gemfile

  gem 'camunda-workflow'

Camunda Integration with Ruby

The process definitions key becomes the module name of your implementation classes and must be set to the name of a ruby style constant (screenshot example provided below). This same process definition key should be set as the topic name for external tasks. Tasks are pulled and fetched and locked and then run. We expect classes (ActiveJob) to implement each external task.

image

Integration with your worker classes

The module ExternalTaskJob should be included in your job implementation classes. The job implementation classes can inherit from ActiveJob::Base, or use Sidekiq::Worker or use some other system for job queuing.

Currently we call perform_later on job implementation classes. If we want to make this more flexible, we need to make the method used to queue jobs configurable. perform_later for ActiveJob, perform_async for Sidekiq, or perform if no background task system is used.

Implementing bpmn_perform

bpmn_perform is your implementation of the service task.

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 

raise Camunda::BpmnError.new error_code: 'bpmn-error', message: "Special BPMN error", variables: { bpmn: 'error' }

Generators

BPMN ActiveJob install

rails generate camunda:install

Creates app/jobs/camunda_job.rb. A class which 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

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. This can be used to start a Camunda instance with a REST api. This can also be deployed to PCF by generating a Spring Boot jar and pushing it.

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

Start the application: mvn spring-boot:run

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.

Engine Route Prefix using 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-engine.

To override the default engine route prefix to allow your rails application to use the route prefix of rest, you need to add an initializer file in your rails app with the below code. 

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

Enable HTTP Basic Auth for Java Spring Boot app

To add authentication to Camunda's REST API within the Java Spring Boot app change the camunda.authentication variable located in the application.properties (bpmn/java_app/src/main/resources) file to true. Creating an environment variable ENV['CAMUNDA_AUTH'] and setting a value of true or false will set the value as well. 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.engine_route_prefix = 'rest'
  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.

Running java unit tests

mvn clean test

Usage

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_name: '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 will run as an infinite loop with long polling to fetch tasks, queue, and run them. Topic is the process definition key, as show 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.

  Camunda::Poller.fetch_and_execute %w[CamundaWorkflow]

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

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

Rspec Helpers

RSpec helpers can will 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

Note:

If you get an error

    ** ERROR: directory is already being watched! **

    Directory: bpmn/java_app/src/main/resources
    is already being watched through: bpmn/diagrams

    MORE INFO: https://github.com/guard/listen/wiki/Duplicate-directory-errors

It is because ActionMailer preview causes test/mailers/previews to get added to the Rails EventedFileChecker by default. RSpec is supposed to override it, but it is not appropriately overridden for EventedFileChecker and/or you don't have spec/mailers/preview existing. If that directory does not exist, it goes to the first common directory that exists, which is your Rails root folder. So EventedFileChecker is listening to your entire Rails folder. Not a big problem, but it causes a problem for our created symlink.

So add: 

    config.action_mailer.show_previews = false

to your development.rb file to solve listen errors about a symlink. Unless you are using ActionMailer previews, in which case you should have the directory created already.

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.