update sqlite plugin docs

docs/config.rst

@@ -313,6 +313,8 @@ The values of the attributes can be either strings, numbers, lists, dictionaries
 Plugins can be used to allocate resources on the server side and then pass the result of the allocation back to the client via the definition. The supported plugins are:
 
 -  **allocate(resource\_pool)** - allocates an available resource from a file-based resource pool
+-  **sqlite(resource\_pool)** - allocates an available resource from a sqlite database
+
 
 .. note::
 
@@ -656,7 +658,7 @@ Actions
 ``[data_root]/actions/`` contains the set of all actions available for use in
 definitions.
 
-New custom actions to-be referenced from definitions can be added to 
+New custom actions to-be referenced from definitions can be added to
 ``[data_root]/actions/``. These will be loaded on-demand and do not require
 a restart of the ZTPServer. See ``[data_root]/actions`` for examples.
 
@@ -765,22 +767,22 @@ just standard EOS configuration blocks.
 Plugins for allocating resources
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-Plugins for allocating resources from resource pools 
-are located in ``[data_root]/plugins/`` and are referenced 
+Plugins for allocating resources from resource pools
+are located in ``[data_root]/plugins/`` and are referenced
 by ``<filename>(<resource_pool>)``.
 
 Each plugin contains a ``main`` function with the following signature:
 
-    def main(node_id, pool): 
+    def main(node_id, pool):
         ...
-        
+
 where:
  - ``node_id`` is the unique_id of the node being provisioned
  - ``pool`` is the name of the resource pool from which an attribute is being allocated
 
-New custom plugins to-be referenced from definitions can be added to 
+New custom plugins to-be referenced from definitions can be added to
 ``[data_root]/plugins/``. These will be loaded on-demand and do not require
-a restart of the ZTPServer. See ``[data_root]/plugins/test`` for a very basic 
+a restart of the ZTPServer. See ``[data_root]/plugins/test`` for a very basic
 example.
 
 **allocate(resource_pool)**
@@ -839,6 +841,57 @@ associated to it back to ``null``, by editing the resource file.
 Alternatively, ``$ztps --clear-resources`` can be used in order to free
 all resources in all file-based resource files.
 
+**sqlite(resource_pool)**
+
+Allocates a resource from a pre-filled sqlite database. The database
+is defined by the global variable, 'DB_URL' within the plugin. The database
+can include multiple tables, but the value passed into the
+'sqlite(resource_pool)' function will be used to look for an available resource.
+
+Table structure should be as follows with the exact column names:
+
+| node_id |   key   |
+|:-------:|---------|
+| NULL    | 1.1.1.1 |
+| NULL    | 1.1.1.2 |
+| NULL    | 1.1.1.3 |
+
+
+Which can be created with statements like:
+
+``CREATE TABLE `mgmt_subnet`(key TEXT, node_id TEXT)``
+
+and add entries with:
+
+``INSERT INTO `mgmt_subnet` VALUES('1.1.1.1', NULL)``
+
+When a resource is added, the node_id row will be updated
+to include the System ID from the switch.
+
+|    node_id   |   key   |
+|--------------|---------|
+| 001122334455 | 1.1.1.1 |
+| NULL         | 1.1.1.2 |
+| NULL         | 1.1.1.3 |
+
+On subsequent attempts to allocate the resource to the same node,
+ztpserver will first check to see whether the node has already been
+allocated a resource from the pool. If it has, it will reuse the
+resource instead of allocating a new one.
+
+Definition example:
+
+```
+    actions:
+      -
+        action: add_config
+        attributes:
+          url: files/templates/ma1.templates
+          variables:
+            ipaddress: sqlite('mgmt_subnet')
+        name: "configure ma1"
+```
+
 Config-handlers
 ~~~~~~~~~~~~~~~