Add architecture diagram

* list Monasca repositories

Task: 14430
Story: 2001912

Change-Id: I40f3af3a1b4d3da25ac92cc2c0ca92f07d476499

doc/source/index.rst

@@ -35,6 +35,65 @@ repositories. Each module is designed to provide a discrete service in the
 overall monitoring solution and can be deployed or omitted according to
 operators/customers needs.
 
+Architecture
+============
+
+The following illustration provides an overview of Monasca's metrics pipeline
+and the interaction of the involved components. For information on Monasca's
+log pipeline, refer to
+`this wiki page <https://wiki.openstack.org/wiki/Monasca/Logging>`_.
+
+.. image:: /_static/images/architecture.png
+  :width: 900 px
+
+Repositories
+------------
+
+* `monasca-api <https://github.com/openstack/monasca-api>`_:
+  RESTful API for metrics, alarms, and notifications.
+* `monasca-agent <https://github.com/openstack/monasca-agent>`_:
+  Agent for retrieving metrics data.
+* `monasca-persister <https://github.com/openstack/monasca-persister>`_:
+  Writes metrics and alarm state transitions to a time-series database.
+* `monasca-thresh <https://github.com/openstack/monasca-thresh>`_:
+  Thresholding engine for computing thresholds on metrics and determining alarm
+  states.
+* `monasca-notification <https://github.com/openstack/monasca-notification>`_:
+  Pluggable notification engine for consuming alarm state transitions and
+  sending notifications for alarms.
+* `monasca-transform <https://github.com/openstack/monasca-transform>`_:
+  Aggregation engine based on Apache Spark.
+* `monasca-aggregator <https://github.com/monasca/monasca-aggregator>`_:
+  Light-weight metrics aggregator.
+
+Apart from sending requests directly to the API, the following tools are
+available for interacting with Monasca:
+
+* `Monasca Client <https://docs.openstack.org/python-monascaclient>`_:
+  CLI and Python client.
+* `Horizon plugin <https://github.com/openstack/monasca-ui>`_:
+  Plugin adding the monitoring panel to Horizon.
+* `Grafana app <https://github.com/monasca/monasca-grafana>`_:
+  Plugin for Grafana to view and configure alarm definitions, alarms, and
+  notifications.
+
+Libraries:
+
+* `monasca-common <https://github.com/openstack/monasca-common>`_:
+  Common code used in the Monasca components.
+* `monasca-statsd <https://github.com/openstack/monasca-statsd>`_:
+  StatsD-compatible library for sending metrics from instrumented applications.
+
+Grafana__ integration:
+
+* `monasca-grafana-datasource
+  <https://github.com/openstack/monasca-grafana-datasource>`_:
+  Multi-tenant Monasca data source for Grafana.
+* `grafana <https://github.com/monasca/grafana>`_:
+  Forked version of Grafana 4.1.2 with Keystone authentication added.
+
+__ https://grafana.com/
+
 For Contributors
 ================