Processus

Processus is a simple, nodejs based, workflow engine designed to help orchestrate multiple tasks.

There are many workflow engines, but Processus makes some very specific assumptions that make it easy to quickly write simple, yet powerful workflows.

• Installation
• Overview
  • Features
  • Workflow
  • Tasks
• User Guide
• Contributing

---

Getting Started

Installation

Install using npm within your project

npm install --save processus

Install globally for use on the command line

npm install -g processus

or clone this repo

git clone https://github.com/cloudb2/processus
cd processus
npm install

Usage CLI

$ ./bin/processus-cli -h

  ____  ____   __    ___  ____  ____  ____  _  _  ____
 (  _ \(  _ \ /  \  / __)(  __)/ ___)/ ___)/ )( \/ ___)
  ) __/ )   /(  O )( (__  ) _) \___  \___ \) \/ (\___ \
 (__)  (__\_) \__/  \___)(____)(____/(____/\____/(____/

           Processus: A Simple Workflow Engine.

Usage:
  processus-cli [OPTIONS] [ARGS]

Options:
  -l, --log [STRING]     Sets the log level
                         [debug|verbose|info|warn|error].  (Default is error)
  -f, --file STRING      Workflow or task definition. A task must also include
                         the workflow ID. For YAML use .yml postfix.
  -i, --id STRING        Workflow ID.
  -r, --rewind NUMBER    time in reverse chronological order. 0 is current, 1
                         is the previous save point etc.
  -d, --delete STRING    delete a workflow instance
      --deleteALL        delete ALL workflow instances.
  -h, --help             Display help and usage details

Usage API

var processus = require('processus');

var wf = {
  "name": "Example Workflow",
  "description": "An example workflow using the API.",
  "tasks":{
    "task 1": {
      "description": "Demo task to execute echo command.",
      "blocking": true,
      "handler" : "../taskhandlers/execHandler",
      "parameters": {
        "cmd": "echo 'Congratulations you called a workflow using the API.'"
      }
    }
  }
};

processus.execute(wf, function(err, workflow){
  if(!err) {
    console.log(workflow.tasks['task 1'].parameters.stdout);
  }
});

Overview

Features

1. Define workflow in JSON or YAML
2. Execute tasks in series (sequentially) or parallel
3. Nested tasks
4. Reference data between tasks
5. Reference data from workflow to tasks
6. Call a workflow from a workflow
7. Extensible task handlers
8. Task handlers included

• testHandler: testing Processus workflows
• execHandler: executing local commands (background tasks now also supported)
• workflowHandler: for calling other workflows
• requestHandler: making HTTP requests
• conditionHandler: evaluating conditional statements
• expectHandler: testing assertions with expect

1. Built in persistence (file based)
2. Inject workflow with additional tasks
3. Pre and Post workflow tasks
4. Support for environment variables
5. Inspect executed workflows and look back through their history
6. Update in-flight (paused) workflows with async callbacks
7. Dockerized API

Workflow

A workflow in Processus is defined using JSON (or equivalent YAML), which should conform to a specific structure. The best way to understand that structure is by looking at examples.

A workflow, in it's simplest form, is defined as follows.

{
  "tasks": {
  },
  "id": "[instance UUID]"
  "status": "[open|error|completed]"
}

Both id and status are added by Processus at execution time.

execute the above example ex1.json using the following command.

../bin/processus-cli -l info -f ./test/ex1.json

You should see something like this.

$ ./bin/processus-cli -l info -f ./test/ex1.json

  ____  ____   __    ___  ____  ____  ____  _  _  ____
 (  _ \(  _ \ /  \  / __)(  __)/ ___)/ ___)/ )( \/ ___)
  ) __/ )   /(  O )( (__  ) _) \___  \___ \) \/ (\___ \
 (__)  (__\_) \__/  \___)(____)(____/(____/\____/(____/

           Processus: A Simple Workflow Engine.

info: reading workflow file [./test/ex1.json]
info: ✰ Workflow [./test/ex1.json] with id [5e4993b8-563f-448e-a983-3f1e0b342d60] exited without error, but did not complete.

Note

1. You can add additional meta data to the workflow such as a name and description, but that will be ignored by Processus.
2. The status of a workflow can be open, error or completed.
3. In this example there are no tasks, so the Processus returns open, assuming that a task will be injected later. More on this later.

execute ex1 again, this time with a log level of debug.

../bin/processus-cli -l debug -f ./test/ex1.json

You should see something like this.

$ ./bin/processus-cli -l debug -f ./test/ex1.json

  ____  ____   __    ___  ____  ____  ____  _  _  ____
 (  _ \(  _ \ /  \  / __)(  __)/ ___)/ ___)/ )( \/ ___)
  ) __/ )   /(  O )( (__  ) _) \___  \___ \) \/ (\___ \
 (__)  (__\_) \__/  \___)(____)(____/(____/\____/(____/

           Processus: A Simple Workflow Engine.

info: reading workflow file [./test/ex1.json]
debug: checking for data directory [_data]
debug: init complete without error.
debug: save point a reached.
debug: save point c reached.
debug: Workflow returned successfully.
debug: {
  "tasks": {},
  "status": "open",
  "id": "bec87e05-d4c4-43e8-b16c-8c89215f28a2"
}
info: ✰ Workflow [./test/ex1.json] with id [bec87e05-d4c4-43e8-b16c-8c89215f28a2] exited without error, but did not complete.

Note

1. The status and id have been added by Processus
2. The workflow remains open as there are NO tasks to execute

Tasks

Consider the following workflow.

{
  "tasks": {
    "say hello": {
      "blocking": true,
      "handler": "../taskhandlers/execHandler",
      "parameters": {
        "cmd": "echo 'hello, world'"
      }
    },
    "say hello again": {
      "blocking": true,
      "handler": "../taskhandlers/execHandler",
      "parameters": {
        "cmd": "echo 'hello, world again'"
      }
    }
  }
}

Note

1. The above workflow has 2 tasks say hello and say hello again.
2. Each task uses a handler called execHandler which executed the command identified in the data property of the task by parameters.cmd.
3. See .yml versions in the test directory for a YAML equivalent workflows. e.g.

---
  tasks:
    say hello:
      blocking: true
      handler: "../taskhandlers/execHandler"
      parameters:
        cmd: "echo 'hello, world'"
    say hello again:
      blocking: true
      handler: "../taskhandlers/execHandler"
      parameters:
        cmd: "echo 'hello, world again'"

So, in short, this simple workflow will execute echo 'hello, world' and echo 'hello, world again' sequentially.

execute ex2.json

./bin/processus-cli -l debug -f ./test/ex2.json

You should see something like this.

$ ./bin/processus-cli -l debug -f ./test/ex2.json

  ____  ____   __    ___  ____  ____  ____  _  _  ____
 (  _ \(  _ \ /  \  / __)(  __)/ ___)/ ___)/ )( \/ ___)
  ) __/ )   /(  O )( (__  ) _) \___  \___ \) \/ (\___ \
 (__)  (__\_) \__/  \___)(____)(____/(____/\____/(____/

           Processus: A Simple Workflow Engine.

info: reading workflow file [./test/ex2.json]
debug: checking for data directory [_data]
debug: init complete without error.
debug: save point a reached.
debug: task.skipIf = undefined
debug: task.errorIf = undefined
info: ⧖ Starting task [say hello]
debug: stdout ➜ [hello, world
]
info: ✔ task [say hello] completed successfully.
debug: save point a reached.
debug: task.skipIf = undefined
debug: task.errorIf = undefined
info: ⧖ Starting task [say hello again]
debug: stdout ➜ [hello, world again
]
info: ✔ task [say hello again] completed successfully.
debug: save point a reached.
debug: save point c reached.
debug: Workflow returned successfully.
debug: {
  "tasks": {
    "say hello": {
      "blocking": true,
      "handler": "../taskhandlers/execHandler",
      "parameters": {
        "cmd": "echo 'hello, world'",
        "stdout": "hello, world\n",
        "stderr": ""
      },
      "status": "completed",
      "timeOpened": 1447974872204,
      "timeStarted": 1447974872206,
      "timeCompleted": 1447974872224,
      "handlerDuration": 18,
      "totalDuration": 20
    },
    "say hello again": {
      "blocking": true,
      "handler": "../taskhandlers/execHandler",
      "parameters": {
        "cmd": "echo 'hello, world again'",
        "stdout": "hello, world again\n",
        "stderr": ""
      },
      "status": "completed",
      "timeOpened": 1447974872225,
      "timeStarted": 1447974872226,
      "timeCompleted": 1447974872235,
      "handlerDuration": 9,
      "totalDuration": 10
    }
  },
  "status": "completed",
  "id": "e83de778-d64b-403f-b29d-c305c9f854dd"
}
info: ✰ Workflow [./test/ex2.json] with id [e83de778-d64b-403f-b29d-c305c9f854dd] completed successfully.

Note

1. The handler has added stdout and stderr to each task's parameters property.
2. The status of each task and the overall workflow is shown as completed
3. Processus has added additional timing information to each task.
4. The status of a task can be one of the following

• waiting It is waiting to be opened by Processus
• open It is opened by Processus
• executing The handler associated with this task is currently executing
• completed The task has completed successfully
• paused A handler has finished executing but a response is paused. i.e. it is expected that the workflow will be updated at some point in the future from an async callback.
• error An error occured during execution of the handler

See the User Guide for much more!

Contributing

Yes, please.

Make a pull requests and ensure you can run ./runtests.sh successfully. Please add additional tests for any new features/mods you make.

Roadmap

• Workflow Persistence Plugin Architecture
  • Add Mongodb persistence type
• Full REST API to interact with Processus
  • Swagger yaml