Added userguide overview (very rough)

docs/userguide/index.rst

@@ -10,6 +10,7 @@
 .. toctree::
     :maxdepth: 2
 
+    overview
     tasks
     executing
     workers

docs/userguide/overview.rst

@@ -0,0 +1,69 @@
+.. _guide-overview:
+
+==========
+ Overview
+==========
+
+.. contents::
+    :local:
+
+.. _overview-figure-1:
+
+.. figure:: ../images/celery-broker-worker-nodes.jpg
+
+    *Figure 1:* Worker and broker nodes.
+
+To use Celery you need at least two main components; a message broker and
+a worker.
+
+The message broker enables clients and workers to communicate through
+messaging.  There are several broker implementations available, the most
+popular being RabbitMQ.
+
+The worker processes messages, and consists of one or more physical (or virtual)
+nodes.
+
+
+Tasks
+=====
+
+The action to take whenever a message of a certain type is received is called
+a "task".
+
+* Go to :ref:`guide-tasks`.
+* Go to :ref:`guide-executing`.
+* Go to :ref:`guide-sets`
+* Go to :ref:`guide-beat`.
+* Go to :ref:`guide-webhooks`.
+
+
+Workers
+=======
+Go to :ref:`guide-worker`.
+
+Monitoring
+==========
+Go to :ref:`guide-monitoring`.
+
+Routing
+=======
+
+.. _overview-figure-2:
+
+.. figure:: ../images/celery-worker-bindings.jpg
+
+    *Figure 2:* Worker bindings.
+
+Go to :ref:`guide-routing`.
+
+Celery takes advantage of AMQPs flexible routing model. Tasks can be routed
+to specific servers, or a cluster of servers by binding workers to different
+queues. A single worker node can be bound to one or more queues.
+is for this to be as simple as possiblealso several
+messaging scenarios are supported, for example round robin, point-to-point,
+broadcast (one-to-many), and more.
+
+Celery aims to hide the complexity of AMQP through features like
+:ref:`routing-automatic`, while still preserving the ability to go
+low level if that should be necessary.
+