cloudformation template for simple slack bot (pingpong)

template.yaml

---
AWSTemplateFormatVersion: 2010-09-09
Description: "Slack bot"
Parameters:
  SlackBotUserOAuthAccessToken:
    Type: String
    Description: "Slack Bot User OAuth Access Token"
Resources:
  # Lambda
  LambdaExecutionRole:
    Type: AWS::IAM::Role
    Properties:
      AssumeRolePolicyDocument:
        Statement:
        - Action:
          - sts:AssumeRole
          Effect: Allow
          Principal:
            Service:
            - lambda.amazonaws.com
      ManagedPolicyArns:
      - arn:aws:iam::aws:policy/PowerUserAccess
      Path: /
      RoleName: lambdaRole
  LambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      Code:
        ZipFile: |
          const https = require('https')

          exports.handler = (slack_event, context, callback) => {
            if(slack_event.type == 'url_verification'){
                callback(null, { challenge: slack_event.challenge })
                return
            }

            if(slack_event.subtype == 'bot_message') {
                callback(null, "OK")
                return
            }

            if(!/ping/.test(slack_event.event.text)) {
                callback(null, "OK")
                return
            }

            postToSlack (
              'pong', 
              slack_event.event.channel, 
              process.env['BOT_USER_OAUTH_ACCESS_TOKEN']
            )
            
            callback(null, "OK")
          }

          function postToSlack (message, channel, access_token) {
            const data = JSON.stringify({
              token: access_token,
              channel: channel,
              text: message,
            })
            
            const options = {
              host: 'slack.com',
              port: 443,
              path: '/api/chat.postMessage',
              method: 'POST',
              headers: {
                'Content-Type': 'application/json; charset=UTF-8',
                'Authorization': `Bearer ${access_token}`
              }
            }
            
            const req = https.request(options);
            
            req.on('error', (e) => { console.log(e.message) })
            req.write(data)
            req.end()
          }
      Description: "Slack bot"
      FunctionName: slack_bot
      Handler: index.handler
      MemorySize: 128
      Role: !GetAtt LambdaExecutionRole.Arn
      Runtime: nodejs6.10
      Timeout: 3
      Environment:
        Variables:
          BOT_USER_OAUTH_ACCESS_TOKEN: !Sub ${SlackBotUserOAuthAccessToken}
  # ApiGateway
  Api:
    Type: "AWS::ApiGateway::RestApi"
    Properties:
      Name: "api"
  Resource:
    Type: "AWS::ApiGateway::Resource"
    DependsOn: "LambdaFunction"
    Properties:
      RestApiId: !Ref Api
      ParentId: !GetAtt Api.RootResourceId  
      PathPart: "slack_bot"
  LambdaPermission:
    Type: "AWS::Lambda::Permission"
    DependsOn: "LambdaFunction"
    Properties:
      FunctionName: !Ref LambdaFunction
      Action: "lambda:InvokeFunction"
      Principal: "apigateway.amazonaws.com"
      SourceArn: !Sub "arn:aws:execute-api:${AWS::Region}:${AWS::AccountId}:${Api}/*/POST/${LambdaFunction}"
  ResourceMethod:
    Type: "AWS::ApiGateway::Method"
    Properties:
      RestApiId: !Ref Api
      ResourceId: !Ref Resource
      AuthorizationType: "None"
      HttpMethod: "POST"
      MethodResponses:
        - StatusCode: 200
          ResponseModels: { "application/json": "Empty" }
      Integration:
        Type: "AWS"
        IntegrationResponses:
          - StatusCode: 200
            ResponseParameters: {}
            ResponseTemplates: {}
        IntegrationHttpMethod: "POST"
        Uri: !Sub "arn:aws:apigateway:${AWS::Region}:lambda:path/2015-03-31/functions/${LambdaFunction.Arn}/invocations"
    DependsOn: "LambdaPermission"
  Deployment:
    Type: "AWS::ApiGateway::Deployment"
    DependsOn: "ResourceMethod"
    Properties:
      Description: "Api gateway Deployment"
      RestApiId: { "Ref" : "Api" }
      StageName: "prod"
      StageDescription:
        Description: "Production Stage"
        MethodSettings:
          - ResourcePath: "/slack_bot"
            HttpMethod: "POST"
Outputs:
  ApiEndpoint:
    Value: !Sub "https://${Api}.execute-api.${AWS::Region}.amazonaws.com/prod/slack_bot"
    Description: "Slack Api Endpoint"