[docs] Add docs on code structure

Additionally restructures the contributor guide.

Change-Id: I869e00b214cacb0dc223e962201944d3ce13526c
Co-Authored-By: Radosław Piliszek <radoslaw.piliszek@gmail.com>

doc/source/contributor/code_structure.rst

@@ -0,0 +1,92 @@
+..
+      Copyright 2020 Leafcloud B.V.
+
+      Licensed under the Apache License, Version 2.0 (the "License"); you may
+      not use this file except in compliance with the License. You may obtain
+      a copy of the License at
+
+          http://www.apache.org/licenses/LICENSE-2.0
+
+      Unless required by applicable law or agreed to in writing, software
+      distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+      WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+      License for the specific language governing permissions and limitations
+      under the License.
+
+=======================
+Masakari Code Structure
+=======================
+
+Getting started with any codebase requires some getting used to the layout of the project,
+this guide is meant to make your journey navigating the code easier.
+All paths are relative to the repository root.
+
+Code layout
+===========
+
+The Python source code for the project can be found in
+``masakari``:
+
+- ``masakari/api`` contains the api service,
+- ``masakari/engine`` contains the engine service.
+
+The data model
+==============
+
+The oslo objects
+----------------
+
+The base datamodel can be found in ``masakari/objects``.
+It uses ``oslo_versionedobjects``.
+
+These objects are used throughout the code, including RPC, REST API and database persistence.
+
+The oslo notifications
+----------------------
+
+The datamodel for oslo notifications (not to be confused with Masakari notifications
+which are one type of Masakari data objects) can be found in
+``masakari/notifications``.
+
+The REST API
+------------
+
+Mappings of the models for the API are in ``masakari/api/openstack/ha/schemas``.
+
+The controllers are in ``masakari/api/openstack/ha``.
+
+The implementations of the actions are in ``masakari/ha/api.py``.
+
+The database (persistence)
+--------------------------
+
+Some objects can be persisted (saved) to the database,
+currently only ``sqlalchemy`` is supported as the backend.
+
+The general interface is in ``masakari/db/api.py``.
+
+The sqlalchemy implementation is in ``masakari/db/sqlalchemy/api.py``.
+
+Database mappings are in ``masakari/db/sqlalchemy/models.py``.
+
+The entry points
+================
+
+The Masakari project has a variety of entry points.
+
+The entry points can be found in the ``entry_points`` section of ``setup.cfg``.
+
+The main entry points
+---------------------
+
+The main entry points are for the engine and the api:
+
+- ``masakari.cmd.api:main``,
+- ``masakari.cmd.engine:main``.
+
+Another interesting one is the entry point for the management CLI, ``masakari.cmd.manage:main``.
+
+The tests
+=========
+
+The tests are located in: ``masakari/tests``.

doc/source/index.rst

@@ -60,8 +60,6 @@ Reference Material
   reference for Masakari.
 * :doc:`Versioned Notifications </user/notifications>`: This provides the list
   of existing versioned notifications with sample payloads.
-* :doc:`Masakari team process <user/process>`
-* :doc:`Getting started with Masakari  <user/how_to_get_involved>`:
   This will help newcomers understand basics of Masakari
 * `Nova Docs <https://docs.openstack.org/nova/latest/index.html>`_: A collection of guides for Nova.
 
@@ -82,11 +80,19 @@ Reference Material
    configuration/recovery_workflow_sample_config.rst
    configuration/sample_config.rst
    configuration/sample_policy.rst
-   install/development.environment.rst
    user/architecture.rst
-   user/how_to_get_involved.rst
    user/notifications.rst
-   user/process.rst
+
+Contributor Guide
+=================
+
+.. toctree::
+   :maxdepth: 2
+
+   user/how_to_get_involved
+   user/process
+   install/development.environment
+   contributor/code_structure
 
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