custom cloudformation resource for scale up adustment

lib/template.js

@@ -470,7 +470,7 @@ module.exports = (options = {}) => {
         MetricAggregationType: 'Average',
         StepAdjustments: [
           {
-            ScalingAdjustment: Math.ceil(options.maxSize / 10),
+            ScalingAdjustment: cf.getAtt(prefixed('CustomScalingResource'), 'ScalingAdjustment'),
             MetricIntervalLowerBound: 0.0
           }
         ]
@@ -664,6 +664,63 @@ module.exports = (options = {}) => {
     }
   };
 
+  Resources[prefixed('ScalingRole')] = {
+    Type: 'AWS::IAM::Role',
+    Properties: {
+      AssumeRolePolicyDocument: {
+        Statement: [
+          {
+            Effect: 'Allow',
+            Principal: { Service: ['lambda.amazonaws.com'] },
+            Action: ['sts:AssumeRole']
+          }
+        ]
+      },
+      Policies: [{
+        PolicyName: 'CustomcfnScalingLambdaLogs',
+        PolicyDocument: {
+          Statement: [
+            {
+              Effect: 'Allow',
+              Action: [
+                'logs:*'
+              ],
+              Resource: 'arn:aws:logs:*:*:*'
+            }
+          ]
+        }
+      }]
+    }
+  },
+
+  Resources[prefixed('ScalingLambda')] = {
+    Type: 'AWS::Lambda::Function',
+    Properties: {
+      Handler: 'index.handler',
+      Role: cf.getAtt(prefixed('ScalingRole'), 'Arn'),
+      Code: {
+        ZipFile: cf.sub(`
+          var response = require('cfn-response');
+          exports.handler = function(event,context){
+            var result = Math.round(Math.max(Math.min(parseInt(event.ResourceProperties.maxSize) / 10, 100), 1));
+            response.send(event, context, response.SUCCESS, { ScalingAdjustment: result });
+          }
+          `)
+      },
+      Runtime: 'nodejs6.10'
+    }
+  };
+
+  Resources[prefixed('CustomScalingResource')] = {
+    Type: 'AWS::CloudFormation::CustomResource',
+    Properties: {
+      ServiceToken: cf.getAtt(prefixed('ScalingLambda'), 'Arn'),
+      maxSize: options.maxSize
+    }
+  };
+
+
+
   const ref = {
     logGroup: cf.ref(prefixed('LogGroup')),
     topic: cf.ref(prefixed('Topic')),