Add documentation on the rebuild strategies

README.rst

@@ -113,9 +113,78 @@ The response, in case of a successful submission, would include the task ID.
         ...
     }
 
-When ``YAML_SUBMIT_ALLOWED`` is enabled, it is also possible to submit
-raw modulemd yaml file by sending ``multipart/form-data`` request with
-input file named as ``yaml``.
+Options:
+
+- ``yaml`` - a string of the input file when submitting a YAML file directly in a
+  ``multipart/form-data`` request. The MBS setting ``YAML_SUBMIT_ALLOWED`` must be set to ``True``
+  for this to be allowed.
+- ``rebuild_strategy`` - a string of the desired rebuild strategy (affects what components get
+  rebuilt). For the available options, please look at the "Rebuild Strategies" section below.
+
+
+Rebuild Strategies
+------------------
+
+To view the available/allowed rebuild strategies on your MBS instance, query the rebuild-strategies
+API.
+
+::
+
+    GET /module-build-service/1/rebuild-strategies/
+
+::
+
+    HTTP 200 OK
+
+::
+
+    {
+      "items": [
+        {
+          "allowed": false,
+          "default": false,
+          "description": "All components will be rebuilt",
+          "name": "all"
+        },
+        {
+          "allowed": true,
+          "default": true,
+          "description": "All components that have changed and those in subsequent batches will be rebuilt",
+          "name": "changed-and-after"
+        },
+        {
+          "allowed": false,
+          "default": false,
+          "description": "All changed components will be rebuilt",
+          "name": "only-changed"
+        }
+      ]
+    }
+
+
+As described in the API, the following rebuild strategies are supported in MBS:
+
+- ``all`` - all components will be rebuilt. This means that even if the components have not changed
+  since the previous build of the module, all components will be rebuilt and not reused.
+- ``changed-after`` - all components that have changed and those in subsequent batches will be
+  rebuilt. Take for example a module with two batches, and each batch has two components. If one of
+  the two components in the first batch is changed, the other component in the batch will be reused
+  while all other components in the module will be rebuilt. By default, MBS only allows this
+  rebuild strategy.
+- ``only-changed`` - all changed components will be rebuilt. This means that all components,
+  regardless of what happened in previous batches, will be reused if they haven't been changed.
+  This strategy is a compromise between ``all`` and ``changed-after``.
+
+To configure the rebuild strategies in MBS, you may configure the following options:
+
+- ``rebuild_strategy`` - a string of the rebuild strategy to use by default. This defaults to
+  ``changed-and-after``.
+- ``rebuild_strategy_allow_override`` - a boolean that determines if a user is allowed to specify
+  the rebuild strategy they want to use when submitting a module build. This defaults to ``False``.
+- ``rebuild_strategies_allowed`` - a list of rebuild strategies that are allowed to be used. This
+  only takes effect if ``rebuild_strategy_allow_override`` is set to ``True``. This defaults to
+  allowing all rebuild strategies that MBS supports.
+
 
 Module build state query
 ------------------------