Contributing Guide

First and foremost, thank you for wanting to contribute! It’s the only way open source works!

Before you dive into writing patches, here are some of the basics:

Making Contributions

Getting Started

We’ll start by assuming you’ve got a working checkout of the repository (if not then please see the Quickstart).

Second, you’ll need to take care of a couple administrative tasks:

  1. Create an account on Launchpad.
  2. Sign the OpenStack Contributor License Agreement and follow the associated instructions to verify your signature.
  3. Join the Horizon Developers team on Launchpad.
  4. Follow the instructions for setting up git-review in your development environment.

Whew! Got all that? Okay! You’re good to go.

Ways To Contribute

The easiest way to get started with Horizon’s code is to pick a bug on Launchpad that interests you, and start working on that. Bugs tagged as low-hanging-fruit are a good place to start. Alternatively, if there’s an OpenStack API feature you would like to see implemented in Horizon feel free to try building it.

If those are too big, there are lots of great ways to get involved without plunging in head-first:

Choosing Issues To Work On

In general, if you want to write code, there are three cases for issues you might want to work on:

  1. Confirmed bugs
  2. Approved blueprints (features)
  3. New bugs you’ve discovered

If you have an idea for a new feature that isn’t in a blueprint yet, it’s a good idea to write the blueprint first, so you don’t end up writing a bunch of code that may not go in the direction the community wants.

For bugs, open the bug first, but if you can reproduce the bug reliably and identify its cause then it’s usually safe to start working on it. However, getting independent confirmation (and verifying that it’s not a duplicate) is always a good idea if you can be patient.

After You Write Your Patch

Once you’ve made your changes, there are a few things to do:

  • Make sure the unit tests pass: ./ for Python, and npm run test for JS.
  • Make sure the linting tasks pass: ./ --pep8 for Python, and npm run lint for JS.
  • Make sure your code is ready for translation: ./ --pseudo de See the Translatability section below for details.
  • Make sure your code is up-to-date with the latest master: git pull --rebase
  • Finally, run git review to upload your changes to Gerrit for review.

The Horizon core developers will be notified of the new review and will examine it in a timely fashion, either offering feedback or approving it to be merged. If the review is approved, it is sent to Jenkins to verify the unit tests pass and it can be merged cleanly. Once Jenkins approves it, the change will be merged to the master repository and it’s time to celebrate!


The community’s guidelines for etiquette are fairly simple:

  • Treat everyone respectfully and professionally.
  • If a bug is “in progress” in the bug tracker, don’t start working on it without contacting the author. Try on IRC, or via the launchpad email contact link. If you don’t get a response after a reasonable time, then go ahead. Checking first avoids duplicate work and makes sure nobody’s toes get stepped on.
  • If a blueprint is assigned, even if it hasn’t been started, be sure you contact the assignee before taking it on. These larger issues often have a history of discussion or specific implementation details that the assignee may be aware of that you are not.
  • Please don’t re-open tickets closed by a core developer. If you disagree with the decision on the ticket, the appropriate solution is to take it up on IRC or the mailing list.
  • Give credit where credit is due; if someone helps you substantially with a piece of code, it’s polite (though not required) to thank them in your commit message.


Horizon gets translated into multiple languages. The pseudo translation tool can be used to verify that code is ready to be translated. The pseudo tool replaces a language’s translation with a complete, fake translation. Then you can verify that your code properly displays fake translations to validate that your code is ready for translation.

Running the pseudo translation tool

  1. Make sure your English po file is up to date: ./ --makemessages
  2. Run the pseudo tool to create pseudo translations. For example, to replace the German translation with a pseudo translation: ./ --pseudo de
  3. Compile the catalog: ./ --compilemessages
  4. Run your development server.
  5. Log in and change to the language you pseudo translated.

It should look weird. More specifically, the translatable segments are going to start and end with a bracket and they are going to have some added characters. For example, “Log In” will become “[~Log In~您好яшçあ]” This is useful because you can inspect for the following, and consider if your code is working like it should:

  • If you see a string in English it’s not translatable. Should it be?
  • If you see brackets next to each other that might be concatenation. Concatenation can make quality translations difficult or impossible. See for additional information.
  • If there is unexpected wrapping/truncation there might not be enough space for translations.
  • If you see a string in the proper translated language, it comes from an external source. (That’s not bad, just sometimes useful to know)
  • If you get new crashes, there is probably a bug.

Don’t forget to cleanup any pseudo translated po files. Those don’t get merged!

Code Style

As a project, Horizon adheres to code quality standards.


We follow PEP8 for all our Python code, and use (available via the shortcut ./ --pep8) to validate that our code meets proper Python style guidelines.


Additionally, we follow Django’s style guide for templates, views, and other miscellany.


The following standards are divided into required and recommended sections. Our main goal in establishing these best practices is to have code that is reliable, readable, and maintainable.



  • The code has to work on the stable and latest versions of Firefox, Chrome, Safari, and Opera web browsers, and on Microsoft Internet Explorer 11 and later.
  • If you turned compression off during development via COMPRESS_ENABLED = False in, re-enable compression and test your code before submitting.
  • Use === as opposed to == for equality checks. The == will do a type cast before comparing, which can lead to unwanted results.


If typecasting is desired, explicit casting is preferred to keep the meaning of your code clear.

  • Keep document reflows to a minimum. DOM manipulation is expensive, and can become a performance issue. If you are accessing the DOM, make sure that you are doing it in the most optimized way. One example is to build up a document fragment and then append the fragment to the DOM in one pass instead of doing multiple smaller DOM updates.

  • Use “strict”, enclosing each JavaScript file inside a self-executing function. The self-executing function keeps the strict scoped to the file, so its variables and methods are not exposed to other JavaScript files in the product.


    Using strict will throw exceptions for common coding errors, like accessing global vars, that normally are not flagged.


      'use strict';
      // code...
  • Use forEach | each when looping whenever possible. AngularJS and jQuery both provide for each loops that provide both iteration and scope.


    angular.forEach(objectToIterateOver, function(value, key) {
      // loop logic


    $.each(objectToIterateOver, function(key, value) {
      // loop logic
  • Do not put variables or functions in the global namespace. There are several reasons why globals are bad, one being that all JavaScript included in an application runs in the same scope. The issue with that is if another script has the same method or variable names they overwrite each other.

  • Always put var in front of your variables. Not putting var in front of a variable puts that variable into the global space, see above.

  • Do not use eval( ). The eval (expression) evaluates the expression passed to it. This can open up your code to security vulnerabilities and other issues.

  • Do not use ‘with object {code}’. The with statement is used to access properties of an object. The issue with with is that its execution is not consistent, so by reading the statement in the code it is not always clear how it is being used.

Readable & Maintainable

  • Give meaningful names to methods and variables.

  • Avoid excessive nesting.

  • Avoid HTML and CSS in JS code. HTML and CSS belong in templates and stylesheets respectively. For example:

    • In our HTML files, we should focus on layout.

      1. Reduce the small/random <script> and <style> elements in HTML.
      2. Avoid in-lining styles into element in HTML. Use attributes and classes instead.
    • In our JS files, we should focus on logic rather than attempting to manipulate/style elements.

      1. Avoid statements such as element.css({property1,property2...}) they belong in a CSS class.

      2. Avoid statements such as $("<div><span>abc</span></div>") they belong in a HTML template file. Use show | hide | clone elements if dynamic content is required.

      3. Avoid using classes for detection purposes only, instead, defer to attributes. For example to find a div:

        <div class="something"></div>
          $(".something").html("Don't find me this way!");

      Is better found like:

      <div data-something></div>
        $("div[data-something]").html("You found me correctly!");
  • Avoid commented-out code.

  • Avoid dead code.


  • Avoid creating instances of the same object repeatedly within the same scope. Instead, assign the object to a variable and re-use the existing object. For example:

    $(document).on('click', function() { /* do something. */ });
    $(document).on('mouseover', function() { /* do something. */ });

    A better approach:

    var $document = $(document);
    $document.on('click', function() { /* do something. */ });
    $document.on('mouseover', function() { /* do something. */ });

    In the first approach a jQuery object for document is created each time. The second approach creates only one jQuery object and reuses it. Each object needs to be created, uses memory, and needs to be garbage collected.



This section is intended as a quick intro to contributing with AngularJS. For more detailed information, check the AngularJS Topic Guide.

“John Papa Style Guide”

The John Papa Style Guide is the primary point of reference for Angular code style. This style guide has been endorsed by the AngularJS team:

"The most current and detailed Angular Style Guide is the
community-driven effort led by John Papa and Todd Motto."


The style guide is found at the below location:

When reviewing / writing, please refer to the sections of this guide. If an issue is encountered, note it with a comment and provide a link back to the specific issue. For example, code should use named functions. A review noting this should provide the following link in the comments:

In addition to John Papa, the following guidelines are divided into required and recommended sections.


  • Scope is not the model (model is your JavaScript Objects). The scope references the model. Use isolate scopes wherever possible.

  • Since Django already uses {{ }}, use {$ $} or {% verbatim %} instead.

  • For localization in Angular files, use the Angular service horizon.framework.util.i18n.gettext. Ensure that the injected dependency is named gettext. For regular Javascript files, use either gettext or ngettext. Only those two methods are recognized by our tools and will be included in the .po file after running ./run_tests --makemessages.

    // Angular
      .factory('myFactory', myFactory);
    myFactory.$inject = ['horizon.framework.util.i18n.gettext'];
    function myFactory(gettext) {
      gettext('translatable text');
    // Javascript
    ngettext('apple', 'apples', count);
    // Not valid
    var _ = gettext;
    _('translatable text');
    $window.gettext('translatable text');


ESLint is a great tool to be used during your code editing to improve JavaScript quality by checking your code against a configurable list of checks. Therefore, JavaScript developers should configure their editors to use ESLint to warn them of any such errors so they can be addressed. Since ESLint has a ton of configuration options to choose from, links are provided below to the options Horizon wants enforced along with the instructions for setting up ESLint for Eclipse, Sublime Text, Notepad++ and WebStorm/PyCharm.

Instructions for setting up ESLint: ESLint setup instructions


ESLint is part of the automated unit tests performed by Jenkins. The automated test use the default configurations, which are less strict than the configurations we recommended to run in your local development environment.


Style guidelines for CSS are currently quite minimal. Do your best to make the code readable and well-organized. Two spaces are preferred for indentation so as to match both the JavaScript and HTML files.

JavaScript and CSS libraries

We do not bundle third-party code in Horizon’s source tree. Instead, we package the required files as XStatic Python packages and add them as dependencies to Horizon. In particular, when you need to add a new third-party JavaScript or CSS library to Horizon, follow those steps:

  1. Check if the library is already packaged as Xstatic on PyPi, by searching for the library name. If it already is, go to step 5. If it is, but not in the right version, contact the original packager.
  2. Package the library as an Xstatic package by following the instructions in Xstatic documentation.
  3. Create a new repository under OpenStack. Use “xstatic-core” and “xstatic-ptl” groups for the ACLs. Make sure to include the publish-to-pypi job.
  4. Setup PyPi to allow OpenStack to publish your package.
  5. Tag your release. That will cause it to be automatically packaged and released to PyPi.
  6. Add the package to global-requirements. Make sure to mention the license.
  7. Add the package to Horizon’s requirements.txt file, to its, and to the _scripts.html or _stylesheets.html templates. Make sure to keep the order alphabetic.


Note that once a package is released, you can not “un-release” it. You should never attempt to modify, delete or rename a released package without a lot of careful planning and feedback from all projects that use it.

For the purpose of fixing packaging mistakes, XStatic has the build number mechanism. Simply fix the error, increment the build number and release the newer package.


Again, readability is paramount; however be conscientious of how the browser will handle whitespace when rendering the output. Two spaces is the preferred indentation style to match all front-end code.


Horizon’s documentation is written in reStructuredText (reST) and uses Sphinx for additional parsing and functionality, and should follow standard practices for writing reST. This includes:

  • Flow paragraphs such that lines wrap at 80 characters or less.
  • Use proper grammar, spelling, capitalization and punctuation at all times.
  • Make use of Sphinx’s autodoc feature to document modules, classes and functions. This keeps the docs close to the source.
  • Where possible, use Sphinx’s cross-reference syntax (e.g. :class:``) when referring to other Horizon components. The better-linked our docs are, the easier they are to use.

Be sure to generate the documentation before submitting a patch for review. Unexpected warnings often appear when building the documentation, and slight reST syntax errors frequently cause links or cross-references not to work correctly.

Documentation is generated with Sphinx using the tox command. To create HTML docs and man pages:

$ tox -e docs

The results are in the doc/build/html and doc/build/man directories respectively.


Simply by convention, we have a few rules about naming:

  • The term “project” is used in place of Keystone’s “tenant” terminology in all user-facing text. The term “tenant” is still used in API code to make things more obvious for developers.
  • The term “dashboard” refers to a top-level dashboard class, and “panel” to the sub-items within a dashboard. Referring to a panel as a dashboard is both confusing and incorrect.

Release Notes

Release notes for a patch should be included in the patch with the associated changes whenever possible. This allow for simpler tracking. It also enables a single cherry pick to be done if the change is backported to a previous release. In some cases, such as a feature that is provided via multiple patches, release notes can be done in a follow-on review.

If the following applies to the patch, a release note is required:

  • The deployer needs to take an action when upgrading
  • A new feature is implemented
  • Function was removed (hopefully it was deprecated)
  • Current behavior is changed
  • A new config option is added that the deployer should consider changing from the default
  • A security bug is fixed

A release note is suggested if a long-standing or important bug is fixed. Otherwise, a release note is not required.

Horizon uses reno to generate release notes. Please read the docs for details. In summary, use

$ tox -e venv -- reno new <bug-,bp-,whatever>

Then edit the sample file that was created and push it with your change.

To see the results:

$ git commit  # Commit the change because reno scans git log.

$ tox -e releasenotes

Then look at the generated release notes files in releasenotes/build/html in your favorite browser.