********************* Hacking on cloud-init ********************* This document describes how to contribute changes to cloud-init. It assumes you have a `GitHub`_ account, and refers to your GitHub user as ``GH_USER`` throughout. Submitting your first pull request ================================== Follow these steps to submit your first pull request to cloud-init: * To contribute to cloud-init, you must sign the Canonical `contributor license agreement`_ * If you have already signed it as an individual, your Launchpad user will be listed in the `contributor-agreement-canonical`_ group. (Unfortunately there is no easy way to check if an organization or company you are doing work for has signed.) * When signing it: * ensure that you fill in the GitHub username field. * when prompted for 'Project contact' or 'Canonical Project Manager', enter 'Rick Harding'. * If your company has signed the CLA for you, please contact us to help in verifying which Launchpad/GitHub accounts are associated with the company. * For any questions or help with the process, please email `Rick Harding `_ with the subject, "Cloud-Init CLA" * You also may contact user ``rick_h`` in the ``#cloud-init`` channel on the Freenode IRC network. * Configure git with your email and name for commit messages. Your name will appear in commit messages and will also be used in changelogs or release notes. Give yourself credit!:: git config user.name "Your Name" git config user.email "Your Email" * Sign into your `GitHub`_ account * Fork the upstream `repository`_ on Github and clicking on the ``Fork`` button * Create a new remote pointing to your personal GitHub repository. .. code:: sh git clone git://github.com/canonical/cloud-init cd cloud-init git remote add GH_USER git@github.com:GH_USER/cloud-init.git git push GH_USER master * Read through the cloud-init `Code Review Process`_, so you understand how your changes will end up in cloud-init's codebase. * Submit your first cloud-init pull request, adding yourself to the in-repository list that we use to track CLA signatures: `tools/.github-cla-signers`_ * See `PR #344`_ and `PR #345`_ for examples of what this pull request should look like. * Note that ``.github-cla-signers`` is sorted alphabetically. * (If you already have a change that you want to submit, you can also include the change to ``tools/.github-cla-signers`` in that pull request, there is no need for two separate PRs.) .. _GitHub: https://github.com .. _Launchpad: https://launchpad.net .. _repository: https://github.com/canonical/cloud-init .. _contributor license agreement: https://ubuntu.com/legal/contributors .. _contributor-agreement-canonical: https://launchpad.net/%7Econtributor-agreement-canonical/+members .. _tools/.github-cla-signers: https://github.com/canonical/cloud-init/blob/master/tools/.github-cla-signers .. _PR #344: https://github.com/canonical/cloud-init/pull/344 .. _PR #345: https://github.com/canonical/cloud-init/pull/345 Transferring CLA Signatures from Launchpad to Github ---------------------------------------------------- For existing contributors who have signed the agreement in Launchpad before the Github username field was included, we need to verify the link between your `Launchpad`_ account and your `GitHub`_ account. To enable us to do this, we ask that you create a branch with both your Launchpad and GitHub usernames against both the Launchpad and GitHub cloud-init repositories. We've added a tool (``tools/migrate-lp-user-to-github``) to the cloud-init repository to handle this migration as automatically as possible. The cloud-init team will review the two merge proposals and verify that the CLA has been signed for the Launchpad user and record the associated GitHub account. Do these things for each feature or bug ======================================= * Create a new topic branch for your work:: git checkout -b my-topic-branch * Make and commit your changes (note, you can make multiple commits, fixes, more commits.):: git commit * Run unit tests and lint/formatting checks with `tox`_:: tox * Push your changes to your personal GitHub repository:: git push -u GH_USER my-topic-branch * Use your browser to create a merge request: - Open the branch on GitHub - You can see a web view of your repository and navigate to the branch at: ``https://github.com/GH_USER/cloud-init/tree/my-topic-branch`` - Click 'Pull Request` - Fill out the pull request title, summarizing the change and a longer message indicating important details about the changes included, like :: Activate the frobnicator. The frobnicator was previously inactive and now runs by default. This may save the world some day. Then, list the bugs you fixed as footers with syntax as shown here. The commit message should be one summary line of less than 74 characters followed by a blank line, and then one or more paragraphs describing the change and why it was needed. This is the message that will be used on the commit when it is sqaushed and merged into trunk. LP: #1 Note that the project continues to use LP: #NNNNN format for closing launchpad bugs rather than GitHub Issues. - Click 'Create Pull Request` Then, someone in the `Ubuntu Server`_ team will review your changes and follow up in the pull request. Look at the `Code Review Process`_ doc to understand the following steps. Feel free to ping and/or join ``#cloud-init`` on freenode irc if you have any questions. .. _tox: https://tox.readthedocs.io/en/latest/ .. _Ubuntu Server: https://github.com/orgs/canonical/teams/ubuntu-server .. _Code Review Process: https://cloudinit.readthedocs.io/en/latest/topics/code_review.html Design ====== This section captures design decisions that are helpful to know when hacking on cloud-init. Cloud Config Modules -------------------- * Any new modules should use underscores in any new config options and not hyphens (e.g. `new_option` and *not* `new-option`). Unit Testing ------------ cloud-init uses `pytest`_ to run its tests, and has tests written both as ``unittest.TestCase`` sub-classes and as un-subclassed pytest tests. The following guidelines should be followed: * For ease of organisation and greater accessibility for developers not familiar with pytest, all cloud-init unit tests must be contained within test classes * Put another way, module-level test functions should not be used * pytest test classes should use `pytest fixtures`_ to share functionality instead of inheritance * As all tests are contained within classes, it is acceptable to mix ``TestCase`` test classes and pytest test classes within the same test file * These can be easily distinguished by their definition: pytest classes will not use inheritance at all (e.g. `TestGetPackageMirrorInfo`_), whereas ``TestCase`` classes will subclass (indirectly) from ``TestCase`` (e.g. `TestPrependBaseCommands`_) * pytest tests should use bare ``assert`` statements, to take advantage of pytest's `assertion introspection`_ * For ``==`` and other commutative assertions, the expected value should be placed before the value under test: ``assert expected_value == function_under_test()`` * As we still support Ubuntu 16.04 (Xenial Xerus), we can only use pytest features that are available in v2.8.7. This is an inexhaustive list of ways in which this may catch you out: * Support for using ``yield`` in ``pytest.fixture`` functions was only introduced in `pytest 3.0`_. Such functions must instead use the ``pytest.yield_fixture`` decorator. * Only the following built-in fixtures are available [#fixture-list]_: * ``cache`` * ``capsys`` * ``capfd`` * ``record_xml_property`` * ``monkeypatch`` * ``pytestconfig`` * ``recwarn`` * ``tmpdir_factory`` * ``tmpdir`` * Variables/parameter names for ``Mock`` or ``MagicMock`` instances should start with ``m_`` to clearly distinguish them from non-mock variables * For example, ``m_readurl`` (which would be a mock for ``readurl``) * The ``assert_*`` methods that are available on ``Mock`` and ``MagicMock`` objects should be avoided, as typos in these method names may not raise ``AttributeError`` (and so can cause tests to silently pass). An important exception: if a ``Mock`` is `autospecced`_ then misspelled assertion methods *will* raise an ``AttributeError``, so these assertion methods may be used on autospecced ``Mock`` objects. For non-autospecced ``Mock`` s, these substitutions can be used (``m`` is assumed to be a ``Mock``): * ``m.assert_any_call(*args, **kwargs)`` => ``assert mock.call(*args, **kwargs) in m.call_args_list`` * ``m.assert_called()`` => ``assert 0 != m.call_count`` * ``m.assert_called_once()`` => ``assert 1 == m.call_count`` * ``m.assert_called_once_with(*args, **kwargs)`` => ``assert [mock.call(*args, **kwargs)] == m.call_args_list`` * ``m.assert_called_with(*args, **kwargs)`` => ``assert mock.call(*args, **kwargs) == m.call_args_list[-1]`` * ``m.assert_has_calls(call_list, any_order=True)`` => ``for call in call_list: assert call in m.call_args_list`` * ``m.assert_has_calls(...)`` and ``m.assert_has_calls(..., any_order=False)`` are not easily replicated in a single statement, so their use when appropriate is acceptable. * ``m.assert_not_called()`` => ``assert 0 == m.call_count`` * Test arguments should be ordered as follows: * ``mock.patch`` arguments. When used as a decorator, ``mock.patch`` partially applies its generated ``Mock`` object as the first argument, so these arguments must go first. * ``pytest.mark.parametrize`` arguments, in the order specified to the ``parametrize`` decorator. These arguments are also provided by a decorator, so it's natural that they sit next to the ``mock.patch`` arguments. * Fixture arguments, alphabetically. These are not provided by a decorator, so they are last, and their order has no defined meaning, so we default to alphabetical. * It follows from this ordering of test arguments (so that we retain the property that arguments left-to-right correspond to decorators bottom-to-top) that test decorators should be ordered as follows: * ``pytest.mark.parametrize`` * ``mock.patch`` * When there are multiple patch calls in a test file for the module it is testing, it may be desirable to capture the shared string prefix for these patch calls in a module-level variable. If used, such variables should be named ``M_PATH`` or, for datasource tests, ``DS_PATH``. .. _pytest: https://docs.pytest.org/ .. _pytest fixtures: https://docs.pytest.org/en/latest/fixture.html .. _TestGetPackageMirrorInfo: https://github.com/canonical/cloud-init/blob/42f69f410ab8850c02b1f53dd67c132aa8ef64f5/cloudinit/distros/tests/test_init.py\#L15 .. _TestPrependBaseCommands: https://github.com/canonical/cloud-init/blob/master/cloudinit/tests/test_subp.py#L9 .. _assertion introspection: https://docs.pytest.org/en/latest/assert.html .. _pytest 3.0: https://docs.pytest.org/en/latest/changelog.html#id1093 .. _autospecced: https://docs.python.org/3.8/library/unittest.mock.html#autospeccing Type Annotations ---------------- The cloud-init codebase uses Python's annotation support for storing type annotations in the style specified by `PEP-484`_. Their use in the codebase is encouraged but with one important caveat: types from the ``typing`` module cannot be used. cloud-init still supports Python 3.4, which doesn't have the ``typing`` module in the stdlib. This means that the use of any types from the ``typing`` module in the codebase would require installation of an additional Python module on platforms using Python 3.4. As such platforms are generally in maintenance mode, the introduction of a new dependency may act as a break in compatibility in practical terms. Similarly, only function annotations are appropriate for use, as the variable annotations specified in `PEP-526`_ were introduced in Python 3.6. .. _PEP-484: https://www.python.org/dev/peps/pep-0484/ .. _PEP-526: https://www.python.org/dev/peps/pep-0526/ .. [#fixture-list] This list of fixtures (with markup) can be reproduced by running:: py.test-3 --fixtures -q | grep "^[^ ]" | grep -v no | sed 's/.*/* ``\0``/' in a xenial lxd container with python3-pytest installed. Feature Flags ------------- .. automodule:: cloudinit.features :members: Ongoing Refactors ================= This captures ongoing refactoring projects in the codebase. This is intended as documentation for developers involved in the refactoring, but also for other developers who may interact with the code being refactored in the meantime. ``cloudinit.net`` -> ``cloudinit.distros.Networking`` Hierarchy --------------------------------------------------------------- ``cloudinit.net`` was imported from the curtin codebase as a chunk, and then modified enough that it integrated with the rest of the cloud-init codebase. Over the ~4 years since, the fact that it is not fully integrated into the ``Distro`` hierarchy has caused several issues. The common pattern of these problems is that the commands used for networking are different across distributions and operating systems. This has lead to ``cloudinit.net`` developing its own "distro determination" logic: `get_interfaces_by_mac`_ is probably the clearest example of this. Currently, these differences are primarily split along Linux/BSD lines. However, it would be short-sighted to only refactor in a way that captures this difference: we can anticipate that differences will develop between Linux-based distros in future, or there may already be differences in tooling that we currently work around in less obvious ways. The high-level plan is to introduce a hierarchy of networking classes in ``cloudinit.distros``, which each ``Distro`` subclass will reference. These will capture the differences between networking on our various distros, while still allowing easy reuse of code between distros that share functionality (e.g. most of the Linux networking behaviour). Callers will call ``distro.net.func`` instead of ``cloudinit.net.func``, which will necessitate access to an instantiated ``Distro`` object. An implementation note: there may be external consumers of the ``cloudinit.net`` module. We don't consider this a public API, so we will be removing it as part of this refactor. However, we will ensure that the new API is complete from its introduction, so that any such consumers can move over to it wholesale. (Note, however, that this new API is still not considered public or stable, and may not replicate the existing API exactly.) In more detail: * The root of this hierarchy will be the ``cloudinit.distros.Networking`` class. This class will have a corresponding method for every ``cloudinit.net`` function that we identify to be involved in refactoring. Initially, these methods' implementations will simply call the corresponding ``cloudinit.net`` function. (This gives us the complete API from day one, for existing consumers.) * As the biggest differentiator in behaviour, the next layer of the hierarchy will be two subclasses: ``LinuxNetworking`` and ``BSDNetworking``. These will be introduced in the initial PR. * When a difference in behaviour for a particular distro is identified, a new ``Networking`` subclass will be created. This new class should generally subclass either ``LinuxNetworking`` or ``BSDNetworking``. * To be clear: ``Networking`` subclasses will only be created when needed, we will not create a full hierarchy of per-``Distro`` subclasses up-front. * Each ``Distro`` class will have a class variable (``cls.networking_cls``) which points at the appropriate networking class (initially this will be either ``LinuxNetworking`` or ``BSDNetworking``). * When ``Distro`` classes are instantiated, they will instantiate ``cls.networking_cls`` and store the instance at ``self.net``. (This will be implemented in ``cloudinit.distros.Distro.__init__``.) * A helper function will be added which will determine the appropriate ``Distro`` subclass for the current system, instantiate it and return its ``net`` attribute. (This is the entry point for existing consumers to migrate to.) * Callers of refactored functions will change from calling ``cloudinit.net.some_func`` to ``distro.net.some_func``, where ``distro`` is an instance of the appropriate ``Distro`` class for this system. (This will require making such an instance available to callers, which will constitute a large part of the work in this project.) After the initial structure is in place, the work in this refactor will consist of replacing the ``cloudinit.net.some_func`` call in each ``cloudinit.distros.Networking`` method with the actual implementation. This can be done incrementally, one function at a time: * pick an unmigrated ``cloudinit.distros.Networking`` method * refactor all of its callers to call the ``distro.net`` method on ``Distro`` instead of the ``cloudinit.net`` function. (This is likely to be the most time-consuming step, as it may require plumbing ``Distro`` objects through to places that previously have not consumed them.) * refactor its implementation from ``cloudinit.net`` into the ``Networking`` hierarchy (e.g. if it has an if/else on BSD, this is the time to put the implementations in their respective subclasses) * ensure that the new implementation has unit tests (either by moving existing tests, or by writing new ones) * finally, remove it (and any other now-unused functions) from cloudinit.net (to avoid having two parallel implementations) References ~~~~~~~~~~ * `Mina Galić's email the the cloud-init ML in 2018`_ (plus its thread) * `Mina Galić's email to the cloud-init ML in 2019`_ (plus its thread) * `PR #363`_, the discussion which prompted finally starting this refactor (and where a lot of the above details were hashed out) .. _get_interfaces_by_mac: https://github.com/canonical/cloud-init/blob/961239749106daead88da483e7319e9268c67cde/cloudinit/net/__init__.py#L810-L818 .. _Mina Galić's email the the cloud-init ML in 2018: https://lists.launchpad.net/cloud-init/msg00185.html .. _Mina Galić's email to the cloud-init ML in 2019: https://lists.launchpad.net/cloud-init/msg00237.html .. _PR #363: https://github.com/canonical/cloud-init/pull/363