HowTo: Create AWS Lambda with Cloudformation

exchange-rate.yaml

AWSTemplateFormatVersion: 2010-09-09
Parameters:
  AwsRegion:
    Type: String
    Default: us-east-1
  # This bucket stores the lambda function package
  LambdaCodeBucket:
    Type: String
    Default: my-lambda
  LambdaCodeKey:
    Type: String
    Default: exchange-rate.zip
  ExchangeRateURL:
    Type: String
    Default: https://api.exchangeratesapi.io/latest
  # This bucket stores the JSON file generated.
  S3Bucket:
    Type: String
    Default: my-output
  S3ObjectKey:
    Type: String
    Default: exchange-rate.json
  S3ObjectCacheMaxAge:
    Type: Number
    Default: 14400
  # This parameter controls trigger interval
  # You can find the expression format in https://docs.aws.amazon.com/AmazonCloudWatch/latest/events/ScheduledEvents.html
  ExchangeRateTriggerRate:
    Type: String
    Default: rate(4 hours)
  ExchangeRateTimeout:
    Type: Number
    Default: 90
Resources:
  ExchangeRateLambdaRole:
    Type: AWS::IAM::Role
    Properties:
      RoleName: my-exchange-rate-lambda-role
      AssumeRolePolicyDocument:
        Statement:
          - Action:
            - sts:AssumeRole
            Effect: Allow
            Principal:
              Service:
              - lambda.amazonaws.com
        Version: 2012-10-17
      ManagedPolicyArns:
        - arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole
      Path: /
      Policies:
        # This policy allows our lambda function to write to S3 bucket
        - PolicyName: LambdaWriteS3Policy
          PolicyDocument:
            Version: 2012-10-17
            Statement:
              - Action:
                - s3:PutObject
                Effect: Allow
                Resource: '*'

  ExchangeRateLambdaFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: my-exchange-rate
      # Handler is file name + '.' + function name
      Handler: index.getExchangeRate
      Runtime: nodejs8.10
      Role: !GetAtt ExchangeRateLambdaRole.Arn
      Code:
        S3Bucket:
          Ref: LambdaCodeBucket
        S3Key:
          Ref: LambdaCodeKey
      Timeout: !Ref ExchangeRateTimeout
      Environment:
        Variables:
          AwsRegion: !Ref AwsRegion
          ExchangeRateURL: !Ref ExchangeRateURL
          S3Bucket: !Ref S3Bucket
          S3ObjectKey: !Ref S3ObjectKey
          S3ObjectCacheMaxAge: !Ref S3ObjectCacheMaxAge

  ExchangeRateLogGroup:
    Type: AWS::Logs::LogGroup
    Properties:
      LogGroupName:
        !Join
          - ''
          - - '/aws'
            - '/lambda'
            - '/'
            - !Ref ExchangeRateLambdaFunction
      RetentionInDays: 1

  # Scheduling rule is defined here
  ExchangeRateSchedule:
    Type: AWS::Events::Rule
    Properties:
      ScheduleExpression: !Ref ExchangeRateTriggerRate
      State: ENABLED
      Targets:
        - Arn: !Sub ${ExchangeRateLambdaFunction.Arn}
          Id: MyExchangeRateSchedule

  # We give permission to scheduler to invoke lambda function
  ExchangeRateSchedulePermission:
    Type: AWS::Lambda::Permission
    Properties:
      Action: lambda:InvokeFunction
      FunctionName: !Sub ${ExchangeRateLambdaFunction.Arn}
      Principal: events.amazonaws.com
      SourceArn: !Sub ${ExchangeRateSchedule.Arn}

  ExchangeRateOutputBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Ref S3Bucket