utask

µTask, the Lighweight Automation Engine

µTask is an automation engine built for the cloud. It is:

• simple to operate: only a postgres DB is required
• secure: all data is encrypted, only visible to authorized users
• extensible: you can develop custom actions in golang

µTask allows you to model business processes in a declarative yaml format. Describe a set of inputs and a graph of actions and their inter-dependencies: µTask will asynchronously handle the execution of each action, working its way around transient errors and keeping a trace of all intermediary states until completion.

Table of contents

• Quick Start
• Configuration
• Authoring Task Templates
• Extending µTask with plugins
• Contributing

Quick start

Build standalone µTask binary:

$ make all

Boot µTask along with its postgres database:

$ docker-compose up

Go to http://localhost:8081/ui/dashboard on your browser, or explore the API schema on http://localhost:8081/unsecured/spec.json.

Request a new task:

Get an overview of all tasks:

Get a detailed view of a running task:

Browse available task templates:

Configuration 🔨

Command line args

The µTask binary accepts the following arguments as binary args or env var. All are optional and have a default value:

• init-path: the directory from where initialization plugins (see "Developing plugins") are loaded in *.so form (default: ./init)
• plugins-path: the directory from where action plugins (see "Developing plugins") are loaded in *.so form (default: ./plugins)
• templates-path: the directory where yaml-formatted task templates are loaded from (default: ./templates)
• region: an arbitrary identifier, to aggregate a running group of µTask instances (commonly containers), and differentiate them from another group, in a separate region (default: default)
• http-port: the port on which the HTTP API listents (default: 8081)
• debug: a boolean flag to activate verbose logs (default: false)
• maintenance-mode: a boolean to switch API to maintenance mode (default: false)

Config keys and files

Checkout the µTask config keys and files README.

Authentication

The vanilla version of µTask doesn't handle authentication by itself, it is meant to be placed behind a reverse proxy that provides a username through the "x-remote-user" http header. A username found there will be trusted as is, and used for authorization purposes (admin actions, task resolution, etc...).

For development purposes, an optional basic-auth configstore item can be provided to define a mapping of usernames and passwords. This is not meant for use in production.

Extending this basic authentication mechanism is possible by developing an "init" plugin, as described below.

Examples

Checkout the µTask examples directory.

Authoring Task Templates

A process that can be executed by µTask is modelled as a task template: it is written in yaml format and describes a sequence of steps, their interdepencies, and additional conditions and constraints to control the flow of execution.

The user that creates a task is called requester, and the user that executes it is called resolver. Both can be the same user in some scenarios.

A user can be allowed to resolve a task in three ways:

• the user is included in the global configuration's list of admin_usernames
• the user is included in the global configuration's list of resolver_usernames
• the user is included in the task's template list of allowed_resolver_usernames

Value Templating

µTask uses the go templating engine in order to introduce dynamic values during a task's execution. As you'll see in the example template below, template handles can be used to access values from different sources. Here's a summary of how you can access values through template handles:

• .input.[INPUT_NAME]: the value of an input provided by the task's requester
• .resolver_input.[INPUT_NAME]: the value of an input provided by the task's resolver
• .step.[STEP_NAME].output.foo: field foo from the output of a named step
• .step.[STEP_NAME].metadata.HTTPStatus: field HTTPStatus from the metadata of a named step
• .config.[CONFIG_ITEM].bar: field bar from a config item (configstore, see above)
• .iterator.foo: field foo from the iterator in a loop (see foreach steps below)

Basic properties

• name: a short unique human-readable identifier
• description: sentence-long description of intent
• long_description: paragraph-long basic documentation
• doc_link: URL for external documentation about the task
• title_format: templateable text, generates a title for a task based on this template
• result_format: templateable map, used to generate a final result object from data collected during execution

Advanced properties

• allowed_resolver_usernames: a list of usernames with the right to resolve a task based on this template
• allow_all_resolver_usernames: boolean (default: false): when true, any user can execute a task based on this template
• auto_runnable; boolean (default: false): when true, the task will be executed directly after being created, IF the requester is an accepted resolver or allow_all_resolver_usernames is true
• blocked: boolean (default: false): no tasks can be created from this template
• hidden: boolean (default: false): the template is not listed on the API, it is concealed to regular users
• retry_max: int (default: 100): maximum amount of consecutive executions of a task based on this template, before being blocked for manual review

Inputs

When creating a new task, a requester needs to provide parameters described as a list of objects under the inputs property of a template. Additional parameters can be requested from a task's resolver user: those are represented under the resolver_inputs property of a template.

An input's definition allows to define validation constraints on the values provided for that input. See example template above.

Input properties

• name: unique name, used to access the value provided by the task's requester
• description: human readable description of the input, meant to give context to the task's requester
• regex: (optional) a regular expression that the provided value must match
• legal_values: (optional) a list of possible values accepted for this input
• collection: boolean (default: false) a list of values is accepted, instead of a single value
• type: (string|number|bool) (default: string) the type of data accepted
• optional: boolean (default: false) the input can be left empty
• default: (optional) a value assigned to the input if left empty

Variables

A template variable is a named holder of either:

• a fixed value
• a JS expression evaluated on the fly.

See the example template above to see variables in action. The expression in a variable can contain template handles to introduce values dynamically (from executed steps, for instance), like a step's configuration.

Steps

A step is the smallest unit of work that can be performed within a task. At is's heart, a step defines an action: several types of actions are available, and each type requires a different configuration, provided as part of the step definition. The state of a step will change during a task's resolution process, and determine which steps become elligible for execution. Custom states can be defined for a step, to fine-tune execution flow (see below).

A sequence of ordered steps constitutes the entire workload of a task. Steps are ordered by declaring dependencies between each other. A step declares its dependencies as a list of step names on which it waits, meaning that a step's execution will be on hold until its dependencies have been resolved. A dependency can be qualified with a step's state. For example, step2 can declare a dependency on step1 in the following ways:

• step1: wait for step1 to be in state DONE
• step1:PRUNE: wait for step1 to be in state PRUNE
• step1:ANY: wait for step1 to be in any "final" state, ie. it cannot keep running

The flow of this sequence can further be controlled with conditions on the steps: a condition is a clause that can be run before or after the step's action. A condition can either be used:

• to skip a step altogether
• to analyze its outcome and override the engine's default behaviour

TODO step.conditions examples

Basic Properties

• name: a unique identifier
• description: a human readable sentence to convey the step's intent
• dependencies: a list of step names on which this step waits before running
• retry_pattern: (seconds|minutes|hours) define on what temporal order of magnitude the re-runs of this step should be spread

Action

The action field of a step defines the actual workload to be performed. It consists of at least a type chosen among the registered action plugins, and a configuration fitting that plugin. See below for a detailed description of builtin plugins. For information on how to develop your own action plugins, refer to this section.

When an action's configuration is repeated across several steps, it can be factored by defining base_configurations at the root of the template. For example:

base_configurations:
  postMessage:
    method: POST
    url: http://message.board/new

This base configuration can then be leveraged by any step wanting to post a message, with different bodies:

steps:
  sayHello:
    description: Say hello on the message board
    action:
      type: http
      base_configuration: postMessage
      configuration:
        body: Hello
  sayGoodbye:
    description: Say goodbye on the message board
    dependencies: [sayHello]
    action:
      type: http
      base_configuration: postMessage
      configuration:
        body: Goodbye

These two step definitions are the equivalent of:

steps:
  sayHello:
    description: Say hello on the message board
    action:
      type: http
      configuration:
        body: Hello
        method: POST
        url: http://message.board/new
  sayGoodbye:
    description: Say goodbye on the message board
    dependencies: [sayHello]
    action:
      type: http
      configuration:
        body: Goodbye
        method: POST
        url: http://message.board/new

The output of an action can be enriched by means of a base_output. For example, in a template with an input field named id, value 1234 and a call to a service which returns the following payload:

{
  "name": "username"
}

The following action definition:

steps:
  getUser:
    description: Prefix an ID received as input, return both
    action:
      type: http
      base_output:
        id: "{{.input.id}}"
      configuration:
        method: GET
        url: http://directory/user/{{.input.id}}

Will render the following output, a combination of the action's raw output and the base_output:

{
  "id": "1234",
  "name": "username"
}

Builtin actions

Loops

A step can be configured to take a json-formatted collection as input, in its foreach property. It will be executed once for each element in the collection, and its result will be a collection of each iteration. This scheme makes it possible to chain several steps with the foreach property.

TODO provide an example

Extending µTask with plugins

TODO

Action Plugins

TODO

Init Plugins

TODO

Contributing

Backend

In order to iterate on feature development, run the utask server plus a backing postgres DB by invoking make run-test-stack-docker in a terminal. Use SIGINT (Ctrl+C) to reboot the server, and SIGQUIT (Ctrl+4) to teardown the server and its DB.

In a separate terminal, rebuild (make re) each time you want to iterate on a code patch, then reboot the server in the terminal where it is running.

Frontend

µTask serves two graphical interfaces: one for general use of the tool (dashboard), the other one for task template authoring (editor). They're found in the ui folder and each have their own Makefile for development purposes.

Run make dev to launch a live-reloading on your machine. The editor is a standalone GUI, while the dashboard needs a backing µTask api (see above to run a server).

Run the tests

Run all test suites against an ephemeral postgres DB:

$ make test-docker

Get in touch

You've developed a new cool feature ? Fixed an annoying bug ? We'll be happy to hear from you! Take a look at CONTRIBUTING.md

Related links

• Contribute: CONTRIBUTING.md
• Report bugs: https://github.com/ovh/utask/issues
• Get latest version: https://github.com/ovh/utask/releases
• License: LICENSE