Policy Templates Documentation

Author: sanathkr

docs/policy_templates.rst

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+Policy Templates
+================
+
+When you define a Serverless Function, SAM automatically creates the IAM Role required to run the function. Let's say
+your function needs to access couple of DynamoDB tables, you need to give your function explicit permissions to access
+the tables. You can do this by adding AWS Managed Policies to Serverless Function resource definition in your SAM 
+template.
+
+For Example:
+
+.. code:: yaml
+
+  MyFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      ...
+      Policies:
+        # Give DynamoDB Full Access to your Lambda Function
+        - AmazonDynamoDBFullAccess
+      ...
+
+  MyTable:
+    Type: AWS::Serverless::SimpleTable
+
+
+Behind the scenes, ``AmazonDynamoDBFullAccess`` will give your function access to **all** DynamoDB APIs against **all**
+DynamoDB tables in **all** regions. This is excessively permissive when all that your function does is Read & Write
+values from the ``MyTable`` created in the stack.
+
+SAM provides a tighter and more secure version of AWS Managed Policies called **Policy Templates**. This are a set of 
+readily availbale policies that can be scoped to a specific resource in the same region where your stack exists. 
+Let's modify the above example to use a policy template called ``DynamoDBCrudPolicy``:
+
+.. code:: yaml
+
+  MyFunction:
+    Type: AWS::Serverless::Function
+    Properties:
+      ...
+      Policies:
+
+        # Give just CRUD permissions to one table
+        - DynamoDBCrudPolicy:
+            TableName: !Ref MyTable
+
+      ...
+
+  MyTable:
+    Type: AWS::Serverless::SimpleTable
+
+
+How to Use
+----------
+
+Policy Templates are specified in ``Policies`` property of AWS::Serverless::Function resource. You can mix policy 
+templates with AWS Managed Policies, custom managed policies or inline policy statements. Behind the scenes
+SAM will expand the policy template to a inline policy statement based on the definition listed in 
+`policy_templates.json`_ file.
+
+Every policy template requires zero or more parameters, which are the resource that this policy is scoped to. 
+Your template will fail to deploy if the value for a required parameter is not specified. You can consult the 
+`policy_templates.json`_ file for name of the policy templates, parameter names as well as the actual policy statement
+it represents. 
+
+If you want a quick reference of all policies, checkout the `all_policy_templates.yaml`_ SAM template in examples 
+folder. 
+
+  NOTE: If a policy template does not require a parameter, you should still specify the value to be an empty dictionary
+  like this:
+
+    .. code: yaml
+
+      Policies:
+        - CloudWatchPutMetricPolicy: {}      
+
+.. _policy_templates.json: policy_templates_data/policy_templates.json
+.. _all_policy_templates.yaml: ../examples/2016-10-31/policy_templates/all_policy_templates.yaml