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Developer Guidelines

Contributors to the Chaos Toolkit are always welcome. This guide describes the general elements you probably need to know to get started. Once past those elements, you should dive into the code of each project and come discuss on our Slack.

Overview

Programming Environment

The programming environment really is up to you. However, since the Chaos Toolkit is implemented in Python so make sure to have the right tooling for it.

The most basics are:

  • Python 3.5+ installed. Right now, we officially support 3.5 and 3.6 but there should not be harm in using 3.7 as long as it can gracefully degrade down to 3.5
  • A virtual environment so you can deploy the dependencies in a specific environment

If you’re not familiar with Python, you will find a few helpful books online, such The Hitchhiker’s Guide to Python.

The Ultimate Trick

Whenever you code on one of the projects, you should run the following command so that the project you are hacking on is part of your virtual environment without being installed:

(chaostk) $ cd <project-name>
(chaostk) $ python setup.py develop

Sometimes, your virtual env may be borked and not point to your development directory. In that case, make sure to remove any previously installed version of the project:

(chaostk) $ pip uninstall <project-name>

Then make sure your virtual environment point at your local directory with:

(chaostk) $ pip freeze

GitHub

The Chaos Toolkit projects are hosted on GitHub. If you wish to contribute, you will need to have an account there.

The general workflow is to fork the project you wish to contribute to, make your changes in a dedicated branch, rebase against the original master and finally submit a pull-request to the project with a clear description of the what and why.

Chaos Toolkit Projects At A Glance

The Chaos Toolkit is made of several projects. The core ones are:

Basically, those projects represent the Chaos Toolkit itself. However, the toolkit is naked without extensions. The currently core extensions are:

In addition, there are a bunch of incubating projects.

Creating an Extension

Please review the various approaches to extend the toolkit.

Creating a Notification Plugin

The Chaos Toolkit triggers events while it runs. Those events may be forwarded to any endpoint that you care for through HTTP or, when you need more control, a full Python project.

There is no template for such a project yet but it is very close to an extension project except it doesn’t have probes and actions. You can therefore start by cloning the extension template project and start from there.

Instead, it should define a function in a module. That function takes two parameters:

  • the notification channel settings (coming from the Chaos Toolkit settings file) as a dictionary
  • the event payload as a Python dictionary which is documented here

The event has a payload key which is the content associated to the event. It can be one of:

  • None when there was no payload ()
  • a string
  • an experiment dictionary
  • an journal dictionary

Three kind of events can be triggered: started, completed and failed for each phase of the flow. Those events are defined here.

A typical notification callback function will look like this:

from typing import Any, Dict

from chaoslib.notification import RunFlowEvent
from chaoslib.types import EventPayload
import logzero

def notify(settings: Dict[str, Any], event: EventPayload):
    if event["name"] == RunFlowEvent.RunStarted.value:
        logzero.info("Event phase " + event["phase"])
        logzero.info("Event timestamp " + event["ts"])
        logzero.info("Event payload " + event["payload"])
        logzero.info("Event error " + event.get("error", "N/A"))

logzero is a third-party package that the Chaos Toolkit uses to log when it runs.