Merge "Add guidelines on adding a new service"

doc/CONTRIBUTING.rst

@@ -40,3 +40,120 @@ https://git.openstack.org/cgit/openstack-dev/sandbox, for learning, understandin
 and testing the `Gerrit Workflow`_.
 
 .. _Gerrit Workflow: http://docs.openstack.org/infra/manual/developers.html#development-workflow
+
+Adding a new service
+====================
+
+Kolla aims to both containerise and deploy all services within the OpenStack
+"big tent". This is a constantly moving target as the ecosystem grows, so these
+guidelines aim to help make adding a new service to Kolla a smooth experience.
+
+The image
+---------
+Kolla follows Docker best practices
+(https://docs.docker.com/engine/userguide/eng-image/dockerfile_best-practices/)
+when designing and implementing services 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.
+
+Images should be created under the ``docker`` directory. OpenStack services
+should inherit from the provided ``openstack-base`` image, while supporting and
+infrastructure services (e.g. mongodb) should inherit from ``base``.
+
+Services consisting of only one service should be placed in an image named the
+same as that service, e.g. ``horizon``. Services that consist of multiple
+processes generally use a base image and child images, e.g. ``glance-base``,
+``glance-api``, and ``glance-registry``.
+
+Jinja2 'blocks' are employed throughout the Dockerfile's to help operators
+customise various stages of the build (refer to
+http://docs.openstack.org/developer/kolla/image-building.html?highlight=override#dockerfile-customisation)
+
+Some of these blocks are free form however, there are a subset that should be
+common to every Dockerfile. The overall structure for a multi container service
+is as follows::
+
+    FROM {{ namespace }}/{{ image_prefix }}openstack-base:{{ tag }}
+    MAINTAINER {{ maintainer }}
+
+    {% import "macros.j2" as macros with context %}
+
+    << binary specific steps >>
+
+    << source specific steps >>
+
+    << common steps >>
+
+    {% block << service >>_footer %}{% endblock %}
+    {% block footer %}{% endblock %}
+    {{ include_footer }}
+
+.. NOTE::
+  The generic footer block ``{% block footer %}{% endblock %}`` should not be
+  included in base images (e.g. glance-base).
+
+  {{ include_footer }} is legacy and should not be included in new services, it
+  is superseded by {% block footer %}{% endblock %}
+
+Orchestration
+-------------
+As of the Newton release there are two main orchestration methods in existence
+for Kolla, Ansible and Kubernetes. Ansible is the most mature and generally
+regarded as the reference implementation.
+
+When adding a role for a new service in Ansible, there are couple of patterns
+that Kolla uses throughout that should be followed.
+
+* The sample inventories
+
+  Entries should be added for the service in each of
+  ``ansible/inventory/multinode`` and ``ansible/inventory/all-in-one``.
+
+* The playbook
+
+  The main playbook that ties all roles together is in ``ansible/site.yml``,
+  this should be updated with appropriate roles, tags, and conditions. Ensure
+  also that supporting hosts such as haproxy are updated when necessary.
+
+* The common role
+
+  A ``common`` role exists which sets up logging, ``kolla-toolbox`` and other
+  supporting components. This should be included in all services within
+  ``meta/main.yml`` of your role.
+
+* Common tasks
+
+  All services should include the following tasks:
+
+  - ``do_reconfigure.yml`` : Used to push new configuration files to the host and
+    restart the service.
+
+  - ``pull.yml`` : Used to pre fetch the image into the Docker image cache on hosts,
+    to speed up intial deploys.
+
+  - ``upgrade.yml`` : Used for upgrading the service in a rolling fashion. May
+    include service specific setup and steps as not all services can be upgraded
+    in the same way.
+
+Other than the above, most roles follow the following pattern::
+
+# Register
+Involves registering the service with Keystone, creating endpoints, roles, users,
+etc.
+
+# Config
+Distributes the config files to the nodes to be pulled into the container on
+startup.
+
+# Bootstrap
+Creating the database (but not tables), database user for the service,
+permissions, etc.
+
+# Bootstrap Service
+Starts a one shot container on the host to create the database tables, and other
+initial run time config.
+
+# Start
+Start the service(s).