Improved architecture section in documentation

Change-Id: I71527cf3831a02f2ce7abbc38c53b5c5d69f99da

doc/source/arch.rst

@@ -5,20 +5,23 @@ CloudKitty's Architecture
 CloudKitty can be cut in four big parts:
 
 * API
-* collector
-* billing processor
-* writer pipeline
+* Collector
+* Rating processing
+* Writing pipeline
+
+
+.. graphviz:: graph/arch.dot
 
 
 Module loading and extensions
 =============================
 
-Nearly every part of CloudKitty makes use of stevedore to load extensions
+Nearly every part of CloudKitty make use of stevedore to load extensions
 dynamically.
 
-Every billing module is loaded at runtime and can be enabled/disabled directly
-via CloudKitty's API. The billing module is responsible of its own API to ease
-the management of its configuration.
+Every rating module is loaded at runtime and can be enabled/disabled directly
+via CloudKitty's API. The module is responsible of its own API to ease the
+management of its configuration.
 
 Collectors and writers are loaded with stevedore but configured in CloudKitty's
 configuration file.
@@ -27,21 +30,115 @@ configuration file.
 Collector
 =========
 
-This part is responsible of the information gathering. It consists of a python
-module that load data from a backend and return them in a format that
-CloudKitty can handle.
+**Loaded with stevedore**
 
-Processor
-=========
+The name of the collector to use is specified in the configuration, only one
+collector can be loaded at once.
+This part is responsible of information gathering. It consists of a python
+class that load data from a backend and return them in a format that CloudKitty
+can handle.
 
-This is where every pricing calculations is done. The data gathered by
-the collector is pushed in a pipeline of billing processors. Every
-processor does its calculations and updates the data.
+The data format of CloudKitty is the following:
+
+.. code-block:: json
+
+   {
+       "myservice": [
+           {
+               "billing": {
+                   "price": 0.1
+               },
+               "desc": {
+                   "sugar": "25",
+                   "fiber": "10",
+                   "name": "apples",
+               },
+               "vol": {
+                   "qty": 1,
+                   "unit": "banana"
+               }
+           }
+       ]
+   }
+
+Example code of a basic collector:
+
+.. code-block:: python
+
+    class MyCollector(BaseCollector):
+        def __init__(self, **kwargs):
+            super(MyCollector, self).__init__(**kwargs)
+
+        def get_mydata(self, start, end=None, project_id=None, q_filter=None):
+            # Do stuff
+            return ck_data
+
+
+You'll now be able to add the gathering of mydata in CloudKitty by modifying
+the configuration and specifying the new service in collect/services.
+
+Rating
+======
+
+**Loaded with stevedore**
+
+This is where every rating calculations is done. The data gathered by the
+collector is pushed in a pipeline of billing processors. Every processor does
+its calculations and updates the data.
+
+Example of minimal rating module (taken from the Noop module):
+
+.. code-block:: python
+
+   class NoopController(billing.BillingController):
+
+    module_name = 'noop'
+
+    def get_module_info(self):
+        module = Noop()
+        infos = {
+            'name': self.module_name,
+            'description': 'Dummy test module.',
+            'enabled': module.enabled,
+            'hot_config': False,
+        }
+        return infos
+
+
+    class Noop(billing.BillingProcessorBase):
+
+        controller = NoopController
+
+        def __init__(self):
+            pass
+
+        @property
+        def enabled(self):
+            """Check if the module is enabled
+
+            :returns: bool if module is enabled
+            """
+            return True
+
+        def reload_config(self):
+            pass
+
+        def process(self, data):
+            for cur_data in data:
+                cur_usage = cur_data['usage']
+                for service in cur_usage:
+                    for entry in cur_usage[service]:
+                        if 'billing' not in entry:
+                            entry['billing'] = {'price': 0}
+            return data
 
 
 Writer
 ======
 
-In the same way as the processor pipeline, the writing is handled with a
-pipeline. The data is pushed to every writer in the pipeline which is
-responsible of the writing.
+**Loaded with stevedore**
+
+In the same way as the rating pipeline, the writing is handled with a pipeline.
+The data is pushed to write orchestrator that will store the data in a
+transient DB (in case of output file invalidation). And then to every writer in
+the pipeline which is responsible of the writing.

doc/source/conf.py

@@ -28,6 +28,7 @@ sys.path.insert(0, os.path.abspath('../..'))
 # ones.
 extensions = [
     'sphinx.ext.autodoc',
+    'sphinx.ext.graphviz',
     'sphinx.ext.intersphinx',
     'sphinx.ext.viewcode',
     'wsmeext.sphinxext',

doc/source/graph/arch.dot

@@ -0,0 +1,59 @@
+digraph "CloudKitty's Architecture" {
+
+    // Graph parameters
+    label="CloudKitty's Internal Architecture";
+    node [shape=box];
+    compound=true;
+
+    // API
+    api [label="API"];
+
+    // Orchestrator
+    subgraph cluster_3 {
+        label="Orchestrator";
+        node[shape=none, width=1.3, height=0, label=""];
+        {rank=same; o1 -> o2 -> o3 [style=invis];}
+    }
+
+    // Collector
+    ceilometer [label="Ceilometer"];
+    vendor [label="Vendor specific", style=dotted];
+    subgraph cluster_0 {
+        label="Collector";
+        style=dashed;
+        ceilometer -> vendor [style=invis];
+    }
+
+    // Rating
+    hashmap [label="HashMap module"];
+    r_others [label="Other modules...", style=dotted];
+    subgraph cluster_1 {
+        label="Rating engines";
+        style=dashed;
+        hashmap -> r_others [style=invis];
+    }
+
+    // Write Orchestrator
+    w_orchestrator [label="Write Orchestrator"];
+    tdb [label="Transient DB"];
+
+    //Writers
+    osrf [label="OpenStack\nReference Format\n(json)"];
+    w_others [label="Other modules...", style=dotted];
+    subgraph cluster_2 {
+        label="Writers";
+        style=dashed;
+        osrf -> w_others [style=invis];
+    }
+
+    // Relations
+    api -> hashmap;
+    api -> r_others;
+    o1 -> ceilometer [dir=both, ltail=cluster_3, lhead=cluster_0];
+    o2 -> hashmap [dir=both, ltail=cluster_3, lhead=cluster_1];
+    o3 -> w_orchestrator [ltail=cluster_3];
+    w_orchestrator -> osrf [constraint=false];
+    w_orchestrator -> w_others [style=dotted, constraint=false];
+    w_orchestrator -> tdb;
+}
+