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.edly.io <http://local.edly.io>`_ (a convenience domain that simply `points at 127.0.0.1 <https://dnschecker.org/#A/local.edly.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 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/quince.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.
- At build time: some of the host directories will be added 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.
After some directories have been added with ``tutor mounts add``, all ``tutor dev`` and ``tutor local`` commands will make use of these bind-mount volumes.
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 ``tutor mounts add`` command. 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.
To check whether you have used the correct syntax, you should run ``tutor mounts list``. This command will indicate whether your folders will be bind-mounted at build time, run time, or both. For instance::
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 ``mounts add ~/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. As an alternative, you should consider following the instructions above: :ref:`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>`__::
..warning:: While the option described below "works", it will only bind-mount directories at run-time. In many cases you really want to bind-mount directories at build-time. For instance: when working on edx-platform requirements. As an alternative, you should consider following the instructions above: :ref:`persistent_mounts`.
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``.
