==================
Adding a new image
==================

Kolla follows `Best practices for writing Dockerfiles
<https://docs.docker.com/engine/userguide/eng-image/dockerfile_best-practices/>`__
where at all possible.

We use ``jinja2`` templating syntax to help manage the volume and complexity
that comes with maintaining multiple Dockerfiles for multiple different base
operating systems.

Dockerfiles should be placed under the ``docker`` directory. OpenStack services
should inherit from the provided ``openstack-base`` image, and
infrastructure services (for example: ``fluentd``) should inherit from
``base``.

Projects consisting of only one service should be placed in an image named the
same as that service, for example: ``horizon``. Services that consist of
multiple processes generally use a base image and child images, for example:
``cinder-base``, ``cinder-api``, ``cinder-scheduler``, ``cinder-volume``,
``cinder-backup``.

Jinja2 `blocks` are employed throughout the Dockerfiles to help operators
customise various stages of the build (refer to :ref:`Dockerfile Customisation
<dockerfile-customisation>`)

Some of these blocks are free form. However, there is a subset that should be
common to every Dockerfile. The overall structure of a Dockerfiles of an
OpenStack project base image is as follows:

.. code-block:: console

   FROM {{ namespace }}/{{ image_prefix }}openstack-base:{{ tag }}
   {% block labels %}
   LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build_date }}"
   {% endblock %}

   {% block << service >>_header %}{% endblock %}

   {% import "macros.j2" as macros with context %}

   << common steps >>

   {% block << service >>_footer %}{% endblock %}
   {% block footer %}{% endblock %}

.. note::

   The generic footer block ``{% block footer %}{% endblock %}`` should **not** be
   included in base images (for example: ``cinder-base``).

It's probably easiest to identify the most similar service being already
provided, copy its Dockerfile structure and amend it to new needs.

Distribution support
====================

By default, every new image should support all supported distributions (CentOS,
Debian, Ubuntu) and both x86-64 and aarch64 architectures. Sometimes it is not
doable so we have list of `unbuildable images` for that.

Unbuildable images
~~~~~~~~~~~~~~~~~~

In ``kolla/image/unbuildable.py`` source file we keep a list of images which
cannot be built for some distribution/architecture/build-type combinations.

.. code-block:: python

   # Note: These are just examples, find the current list at
   # https://github.com/openstack/kolla/blob/4c31f7a3f2002d77dd715dfbb5c2eb74192149d4/kolla/image/unbuildable.py
   UNBUILDABLE_IMAGES = {
       'aarch64': {
           "bifrost-base",    # someone need to get upstream working first
       },

       'centos': {
           "hacluster-pcs",   # Missing crmsh package
       },

       'ubuntu+aarch64': {
           "kibana",          # no binary package
       },
   }

If your new image has some unbuildable combinations, please add it into proper
place in this list. If you are not sure, write it in code review comment and
check CI results of your patch.

.. note::
   Please do not overuse this list -- it is meant as last hope solution.
