Initial publish

Author: Hans Klunder

README.md

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+Docker Voting App done Serverless Style
+=======================================
+
+# Introduction
+I was reading [Deploy the Voting App to AWS ECS with Fargate] by Tony Pujals where he describes how to run the [Docker Voting app demo] on AWS using [AWS Fargate]
+
+  [Deploy the Voting App to AWS ECS with Fargate]:https://medium.com/@tonypujals/deploy-the-voting-app-to-aws-ecs-with-fargate-
+  [Docker Voting app demo]:https://github.com/subfuzion/docker-voting-app-nodejs
+  [AWS Fargate]:https://aws.amazon.com/fargate/
+
+Of course I understand that the Docker Voting app is a showcase of Docker technology and that it's not the most exciting application from a business perspective. I also understand that people want to show how you can take Docker technology to AWS. However in my mind I started wondering: if I would take this to AWS would I be following the same path ? Or would I go Serverless ?
+
+Given the title: I went Serverless!
+
+The voting application is recreated using AWS ApiGateway and AWS DynamoDB only. The queue service could be implemented using SNS, however one typically uses a queue to ensure scalability of the database or to allow for maintenance. Both are handled by AWS DynamoDB automatically.
+
+# Creating the schema
+Looking at the sources of the voting app there are two endpoints:
+- POST /vote where you can post a vote by posting JSON like `{"vote":"a"}` or `{"vote":"b"}`
+- GET /results which will give you results like:
+```json
+{
+  "success" : true,
+  "result" : {
+    "a" : 0,
+    "b" : 0
+     }
+}
+```
+
+Creating a JSON schema produces the following for /vote
+
+```json
+{
+  "Vote": {
+    "type": "object",
+    "required": ["vote"],
+    "properties": {
+      "vote": {
+        "type": "string",
+        "enum": ["a", "b"]
+      }
+    },
+    "title": "Vote Schema"
+  }
+}
+```
+and for /results
+
+```json
+{
+  "type": "object",
+  "properties": {
+    "success": {
+      "type": "boolean"
+    },
+    "result": {
+      "type": "object",
+      "properties": {
+        "a": {
+          "type": "integer"
+        },
+        "b": {
+          "type": "integer"
+        }
+      }
+    }
+  },
+  "title": "Results schema"
+}
+```
+
+Loading these in APIgateway ensures for /vote that only valid POST requests are accepted.
+
+# DynamoDB
+The DynamoDB instance with partion key `topic` only holds one record with `topic` value `default` and a numeric value for `a` and `b`
+
+# APIgateway integration
+A succesful POST operation must result in a increment of the counter for the subject of the vote in the database.
+This is achieved by adding the following integration request mapping template to the POST operation:
+```json
+{
+    "TableName" : "VoteAppDynamoDBTable",
+    "Key": {
+        "topic": {
+            "S":"default"
+        }
+     },
+    "UpdateExpression": "ADD $input.path('$.vote') :inc",
+    "ExpressionAttributeValues": {
+        ":inc": {
+          "N": "1"
+        }
+    }
+}
+```
+This, together with the rest of the integration configuration, will transform the POST operation into a call to DynamoDB to increment the number of votes for the subject provided.
+
+Then when pulling results the GET operation needs to be transformed into a query on DynamoDB using an integration request mapping template
+```json
+{
+    "TableName" : "VoteAppDynamoDBTable",
+    "KeyConditionExpression": "topic = :v1",
+    "ExpressionAttributeValues": {
+        ":v1": {
+            "S": "default"
+        }
+    }
+}
+```
+and the response needs to be mapped to the schema listed above using an integration response mapping template
+```
+#set($inputRoot = $input.path('$'))
+{
+  "success" : true,
+  "result" : {
+#if($inputRoot.Count==0)
+    "a" : 0,
+    "b" : 0
+#{else}
+    "a" : #if($inputRoot.Items[0].a=="")0#{else}$inputRoot.Items[0].a.N#end,
+    "b" : #if($inputRoot.Items[0].b=="")0#{else}$inputRoot.Items[0].b.N#end
+#end
+     }
+}
+```
+As long as no votes have been casted it could be that the whole record does not exist yet or that `a` or `b` is still non-existent. This template takes care of these edge cases.
+
+The full template can be found [here].
+
+  [here]:voteApp-CF-template.json