In addition to running Open edX in production, Tutor can be used for local development of Open edX. This means that it is possible to hack on Open edX without setting up a Virtual Machine. Essentially, this replaces the devstack provided by edX.
Firstly, either :ref:`install Tutor <install>` (for development against the named releases of Open edX) or :ref:`install Tutor Nightly <nightly>` (for development against Open edX's master branches).
* build the "openedx-dev" Docker image, which is based on the "openedx" production image but is `specialized for developer usage`_ (eventually with your fork),
* set ``LMS_HOST`` to `local.overhang.io <http://local.overhang.io>`_ (a convenience domain that simply `points at 127.0.0.1 <https://dnschecker.org/#A/local.overhang.io>`_),
Once first-time setup has been performed with ``launch``, the platform can be started going forward with the lighter-weight ``start -d`` command, which brings up containers *detached* (that is: in the background), but does not perform any initialization tasks::
Finally, the platform can also be started back up with ``launch``. It will take longer than ``start``, but it will ensure that config is applied, databases are provisioned & migrated, plugins are fully initialized, and (if applicable) the bind-mounted edx-platform is set up. Notably, ``launch`` is idempotent, so it is always safe to run it again without risk to data. Including the ``--pullimages`` flag will also ensure that container images are up-to-date::
To debug a local edx-platform repository, add a `python breakpoint <https://docs.python.org/3/library/functions.html#breakpoint>`__ with ``breakpoint()`` anywhere in the code. Then, attach to the applicable service's container by running ``start`` (without ``-d``) followed by the service's name::
To run any command inside one of the containers, run ``tutor dev run [OPTIONS] SERVICE [COMMAND] [ARGS]...``. For instance, to open a bash shell in the LMS or CMS containers::
The ``openedx-dev`` Docker image is based on the same ``openedx`` image used by ``tutor local ...`` to run LMS and CMS. However, it has a few differences to make it more convenient for developers:
- The user that runs inside the container has the same UID as the user on the host, to avoid permission problems inside mounted volumes (and in particular in the edx-platform repository).
- Additional Python and system requirements are installed for convenient debugging: `ipython <https://ipython.org/>`__, `ipdb <https://pypi.org/project/ipdb/>`__, vim, telnet.
- The edx-platform `development requirements <https://github.com/openedx/edx-platform/blob/open-release/palm.master/requirements/edx/development.in>`__ are installed.
It may sometimes be convenient to mount container directories on the host, for instance: for editing and debugging. Tutor provides different solutions to this problem.
``MOUNTS`` is a Tutor setting to bind-mount host directories both at build time and run time:
- At build time: plugins can automatically add certain directories listed in this setting to the `Docker build context <https://docs.docker.com/engine/reference/commandline/buildx_build/#build-context>`__. This makes it possible to transparently build a Docker image using a locally checked-out repository.
- At run time: host directories will be bind-mounted in running containers, using either an automatic or a manual configuration.
After some values have been added to the ``MOUNTS`` setting, all ``tutor dev`` and ``tutor local`` commands will make use of these bind-mount volumes.
With the explicit form, the setting means "bind-mount the host folder /path/to/edx-platform to /openedx/edx-platform in the lms container at run time".
If you use the explicit format, you will quickly realise that you usually want to bind-mount folders in multiple containers at a time. For instance, you will want to bind-mount the edx-platform repository in the "cms" container, but also the "lms-worker" and "cms-worker" containers. To do that, write instead::
This command line is a bit cumbersome. In addition, with this explicit form, the edx-platform repository will *not* be added to the build context at build time. But Tutor can be smart about bind-mounting folders to the right containers in the right place when you use the implicit form of the ``MOUNTS`` setting. For instance, the following implicit form can be used instead of the explicit form above::
With this implicit form, the edx-platform repo will be bind-mounted in the containers at run time, just like with the explicit form. But in addition, the edx-platform will also automatically be added to the Docker image at build time.
So, when should you *not* be using the implicit form? That would be when Tutor does not know where to bind-mount your host folders. For instance, if you wanted to bind-mount your edx-platform virtual environment located in ``~/venvs/edx-platform``, you should not write ``--append MOUNTS=~/venvs/edx-platform``, because that folder would be mounted in a way that would override the edx-platform repository in the container. Instead, you should write::
Sometimes, you may want to modify some of the files inside a container for which you don't have a copy on the host. A typical example is when you want to troubleshoot a Python dependency that is installed inside the application virtual environment. In such cases, you want to first copy the contents of the virtual environment from the container to the local filesystem. To that end, Tutor provides the ``tutor dev copyfrom`` command. First, copy the contents of the container folder to the local filesystem::
..warning:: Manually bind-mounting volumes with the ``--volume`` option makes it difficult to simultaneously bind-mount to multiple containers. Also, the ``--volume`` options are not compatible with ``start`` commands. For an alternative, see the :ref:`persistent mounts <persistent_mounts>`.
The above solution may not work for you if you already have an existing directory, outside of the "volumes/" directory, which you would like mounted in one of your containers. For instance, you may want to mount your copy of the `edx-platform <https://github.com/openedx/edx-platform/>`__ repository. In such cases, you can simply use the ``-v/--volume```Docker option <https://docs.docker.com/storage/volumes/#choose-the--v-or---mount-flag>`__::
Adding items to the ``MOUNTS`` setting effectively adds new bind-mount volumes to the ``docker-compose.yml`` files. But you might want to have more control over your volumes, such as adding read-only options, or customising other fields of the different services. To address these issues, you can create a ``docker-compose.override.yml`` file that will specify custom volumes to be used with all ``dev`` commands::
This override file will be loaded when running any ``tutor dev ..`` command. The edx-platform repo mounted at the specified path will be automatically mounted inside all LMS and CMS containers.
The ``tutor local`` commands load the ``docker-compose.override.yml`` file from the ``$(tutor config printroot)/env/local/docker-compose.override.yml`` directory. One-time jobs from initialisation commands load the ``local/docker-compose.jobs.override.yml`` and ``dev/docker-compose.jobs.override.yml``.
In some cases, you will have to develop features for packages that are pip-installed next to the edx-platform. This is quite easy with Tutor. Just add your packages to the ``$(tutor config printroot)/env/build/openedx/requirements/private.txt`` file. To avoid re-building the openedx Docker image at every change, you should add your package in editable mode. For instance::
You should then run the development server as usual, with ``start``. Every change made to the ``mypackage`` folder will be picked up and the development server will be automatically reloaded.
It's possible to run the full set of unit tests that ship with `edx-platform <https://github.com/openedx/edx-platform/>`__. To do so, run a shell in the LMS development container::
Getting all edx-platform unit tests to pass on Tutor is currently a work-in-progress. Some unit tests are still failing. If you manage to fix some of these, please report your findings in the `Open edX forum <https://discuss.openedx.org/tag/tutor>`__.
