Table of Contents
- Getting Started
- Code components and layout
- Coding style
- Mypy type annotations
- Submitting a pull request
- Asking for help
- Updating certbot-auto and letsencrypt-auto
- Updating the documentation
- Running the client with Docker
- Notes on OS dependencies
Certbot has the same system requirements when set up for development. While the section below will help you install Certbot and its dependencies, Certbot needs to be run on a UNIX-like OS so if you’re using Windows, you’ll need to set up a (virtual) machine running an OS such as Linux and continue with these instructions on that UNIX-like OS.
Running the client in developer mode from your local tree is a little different than running Certbot as a user. To get set up, clone our git repository by running:
git clone https://github.com/certbot/certbot
If you’re on macOS, we recommend you skip the rest of this section and instead run Certbot in Docker. You can find instructions for how to do this here. If you’re running on Linux, you can run the following commands to install dependencies and set up a virtual environment where you can run Certbot.
cd certbot ./certbot-auto --debug --os-packages-only tools/venv.sh
If you have Python3 available and want to use it, run the
You may need to repeat this when Certbot’s dependencies change or when a new plugin is introduced.
You can now run the copy of Certbot from git either by executing
venv/bin/certbot, or by activating the virtual environment. You can do the
latter by running:
source venv/bin/activate # or source venv3/bin/activate
After running this command,
certbot and development tools like
tox are available in the shell where you ran
the command. These tools are installed in the virtual environment and are kept
separate from your global Python installation. This works by setting
environment variables so the right executables are found and Python can pull in
the versions of various packages needed by Certbot. More information can be
found in the virtualenv docs.
You can find the open issues in the github issue tracker. Comparatively easy ones are marked good first issue. If you’re starting work on something, post a comment to let others know and seek feedback on your plan where appropriate.
Once you’ve got a working branch, you can open a pull request. All changes in your pull request must have thorough unit test coverage, pass our tests, and be compliant with the coding style.
When you are working in a file
foo.py, there should also be a file
either in the same directory as
foo.py or in the
(if there isn’t, make one). While you are working on your code and tests, run
python foo_test.py to run the relevant tests.
For debugging, we recommend putting
import ipdb; ipdb.set_trace() statements inside the source code.
Once you are done with your code changes, and the tests in
run all of the unittests for Certbot with
tox -e py27 (this uses Python
Once all the unittests pass, check for sufficient test coverage using
tox -e cover, and then check for code style with
tox -e lint (all files)
pylint --rcfile=.pylintrc path/to/file.py (single file at a time).
Once all of the above is successful, you may run the full test suite using
tox --skip-missing-interpreters. We recommend running the commands above
first, because running all tests like this is very slow, and the large amount
of output can make it hard to find specific failures when they happen.
The full test suite may attempt to modify your system’s Apache config if your user has sudo permissions, so it should not be run on a production Apache server.
Generally it is sufficient to open a pull request and let Github and Travis run integration tests for you, however, if you want to run them locally you need Docker and docker-compose installed and working. Fetch and start Boulder, Let’s Encrypt’s ACME CA software, by using:
If you have problems with Docker, you may want to try removing all containers and volumes and making sure you have at least 1GB of memory.
Set up a certbot_test alias that enables easily running against the local Boulder:
export SERVER=http://localhost:4000/directory source tests/integration/_common.sh
Run the integration tests using:
- contains all protocol specific code
- main client code
- certbot-apache and certbot-nginx
- client code to configure specific web servers
- configuration for packaging Certbot
Certbot has a plugin architecture to facilitate support for different webservers, other TLS servers, and operating systems. The interfaces available for plugins to implement are defined in interfaces.py and plugins/common.py.
The main two plugin interfaces are
implements various ways of proving domain control to a certificate authority,
IInstaller, which configures a server to use a
certificate once it is issued. Some plugins, like the built-in Apache and Nginx
plugins, implement both interfaces and perform both tasks. Others, like the
built-in Standalone authenticator, implement just one interface.
There are also
which can change how prompts are displayed to a user.
Authenticators are plugins that prove control of a domain name by solving a
challenge provided by the ACME server. ACME currently defines three types of
challenges: HTTP, TLS-SNI, and DNS, represented by classes in
An authenticator plugin should implement support for at least one challenge type.
An Authenticator indicates which challenges it supports by implementing
get_chall_pref(domain) to return a sorted list of challenge types in
An Authenticator must also implement
perform(achalls), which “performs” a list
of challenges by, for instance, provisioning a file on an HTTP server, or
setting a TXT record in DNS. Once all challenges have succeeded or failed,
Certbot will call the plugin’s
cleanup(achalls) method to remove any files or
DNS records that were needed only during authentication.
Installers plugins exist to actually setup the certificate in a server,
possibly tweak the security configuration to make it more correct and secure
(Fix some mixed content problems, turn on HSTS, redirect to HTTPS, etc).
Installer plugins tell the main client about their abilities to do the latter
supported_enhancements() call. We currently
have two Installers in the tree, the
ApacheConfigurator. and the
NginxConfigurator. External projects have made some progress toward
support for IIS, Icecast and Plesk.
Installers and Authenticators will oftentimes be the same class/object (because for instance both tasks can be performed by a webserver like nginx) though this is not always the case (the standalone plugin is an authenticator that listens on port 443, but it cannot install certs; a postfix plugin would be an installer but not an authenticator).
Installers and Authenticators are kept separate because
it should be possible to use the
StandaloneAuthenticator (it sets
up its own Python server to perform challenges) with a program that
cannot solve challenges itself (Such as MTA installers).
There are a few existing classes that may be beneficial while
developing a new
Installers aimed to reconfigure UNIX servers may use Augeas for
configuration parsing and can inherit from
to handle much of the interface. Installers that are unable to use
Augeas may still find the
Reverter class helpful in handling
configuration checkpoints and rollback.
Certbot client supports dynamic discovery of plugins through the
setuptools entry points using the
certbot.plugins group. This
way you can, for example, create a custom implementation of
IAuthenticator or the
IInstaller without having to merge it
with the core upstream source code. An example is provided in
While developing, you can install your plugin into a Certbot development virtualenv like this:
. venv/bin/activate . tests/integration/_common.sh pip install -e examples/plugins/ certbot_test plugins
Your plugin should show up in the output of the last command. If not, it was not installed properly.
Once you’ve finished your plugin and published it, you can have your
users install it system-wide with
pip install. Note that this will
only work for users who have Certbot installed from OS packages or via
pip. Users who run
certbot-auto are currently unable to use third-party
plugins. It’s technically possible to install third-party plugins into
the virtualenv used by
certbot-auto, but they will be wiped away when
Please be aware though that as this client is still in a developer-preview stage, the API may undergo a few changes. If you believe the plugin will be beneficial to the community, please consider submitting a pull request to the repo and we will update it with any necessary API changes.
Be consistent with the rest of the code.
def foo(arg): """Short description. :param int arg: Some number. :returns: Argument :rtype: int """ return arg
Remember to use
Certbot uses the mypy static type checker. Python 3 natively supports official type annotations, which can then be tested for consistency using mypy. Python 2 doesn’t, but type annotations can be added in comments. Mypy does some type checks even without type annotations; we can find bugs in Certbot even without a fully annotated codebase.
Certbot supports both Python 2 and 3, so we’re using Python 2-style annotations.
Zulip wrote a great guide to using mypy. It’s useful, but you don’t have to read the whole thing to start contributing to Certbot.
To run mypy on Certbot, use
tox -e mypy on a machine that has Python 3 installed.
Note that instead of just importing
typing, due to packaging issues, in Certbot we import from
acme.magic_typing and have to add some comments for pylint like this:
from acme.magic_typing import Dict # pylint: disable=unused-import, no-name-in-module
Also note that OpenSSL, which we rely on, has type definitions for crypto but not SSL. We use both. Those imports should look like this:
from OpenSSL import crypto from OpenSSL import SSL # type: ignore # https://github.com/python/typeshed/issues/2052
- Write your code!
- Make sure your environment is set up properly and that you’re in your
virtualenv. You can do this by running
./tools/venv.sh. (this is a very important step)
tox -e lintto check for pylint errors. Fix any errors.
tox --skip-missing-interpretersto run the entire test suite including coverage. The
--skip-missing-interpretersargument ignores missing versions of Python needed for running the tests. Fix any errors.
- Submit the PR.
- Did your tests pass on Travis? If they didn’t, fix any errors.
If you have any questions while working on a Certbot issue, don’t hesitate to ask for help! You can do this in the #letsencrypt-dev IRC channel on Freenode. If you don’t already have an IRC client set up, we recommend you join using Riot.
Developers should not modify the
in the root directory of the repository. Rather, modify the
letsencrypt-auto.template and associated platform-specific shell scripts in
letsencrypt-auto-source/pieces/bootstrappers directory, respectively.
Once changes to any of the aforementioned files have been made, the
letsencrypt-auto-source/letsencrypt-auto script should be updated. In lieu of
manually updating this script, run the build script, which lives at
build.py will update the
script. Note that the
letsencrypt-auto scripts in the root
directory of the repository will remain unchanged after this script is run.
Your changes will be propagated to these files during the next release of
When opening a PR, ensure that the following files are committed:
It might also be a good idea to double check that no changes were
inadvertently made to the
letsencrypt-auto scripts in the
root of the repository. These scripts will be updated by the core developers
during the next release.
In order to generate the Sphinx documentation, run the following commands:
make -C docs clean html man
This should generate documentation in the
If you skipped the “Getting Started” instructions above,
pip install -e ".[docs]" to install Certbot’s docs extras modules.
You can use Docker Compose to quickly set up an environment for running and testing Certbot. To install Docker Compose, follow the instructions at https://docs.docker.com/compose/install/.
Linux users can simply run
pip install docker-compose to get
Docker Compose after installing Docker Engine and activating your shell as
described in the Getting Started section.
Now you can develop on your host machine, but run Certbot and test your changes
in Docker. When using
docker-compose make sure you are inside your clone of
the Certbot repository. As an example, you can run the following command to
check for linting errors:
docker-compose run --rm --service-ports development bash -c 'tox -e lint'
You can also leave a terminal open running a shell in the Docker container and modify Certbot code in another window. The Certbot repo on your host machine is mounted inside of the container so any changes you make immediately take effect. To do this, run:
docker-compose run --rm --service-ports development bash
Now running the check for linting errors described above is as easy as:
tox -e lint
OS-level dependencies can be installed like so:
./certbot-auto --debug --os-packages-only