In the previous post Deploying AWS Lambda Functions with AWS SAM, we saw how easy it is to deploy an AWS Lambda function with Amazon API Gateway. Today we want to complement it by using SNS and SQS as triggers for the Lambda function when dealing with event-driven architectures.

Pre-requisites

• Have an IAM User with programmatic access.

• Install the Amazon Lambda Templates (dotnet new -i Amazon.Lambda.Templates)

• Install the Amazon Lambda Tools (dotnet tool install -g Amazon.Lambda.Tools)

• Install AWS SAM CLI.

SQS

Main features:

• Lambda polls the SQS queue and invokes the function synchronously.

• Lambda can read messages in batches and invoke the function once per batch.

• On errors, the message is automatically returned to the queue.

Create a Lambda function to handle SQS events running the following command:

dotnet new lambda.SQS -n SQSTrigger -o .

Create a template.yaml file with the following content:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  SQS

Globals:
  Function:
    Timeout: 15
    MemorySize: 512
    Runtime: dotnet6
    Architectures:
      - x86_64

Resources:
  SQSQueue:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: "mySQSQueue"

  SQSFunction:
    Type: AWS::Serverless::Function
    Properties:
      Runtime: dotnet6
      Handler: SQSTrigger::SQSTrigger.Function::FunctionHandler
      CodeUri: ./src/SQSTrigger/
      Policies:  
        - SQSPollerPolicy:
            QueueName: !GetAtt SQSQueue.QueueName
      Events:
        SQSEvent:
          Type: SQS
          Properties:
            Queue: !GetAtt SQSQueue.Arn
            BatchSize: 10

Outputs:
  SQSConsumerFunction:
    Description: SQS consumer function name
    Value: !Ref SQSFunction

The event type SQS has the following properties:

• BatchSize: Number of records that will be read at once and delivered to the function.

• Queue: The ARN of the queue.

• FilterCriteria: Defines the criteria to determine whether Lambda should process an event.

• FunctionResponseTypes: A list of the response types currently applied to the event source mapping. There is only one value allowed ReportBatchItemFailures.

• MaximumBatchingWindowInSeconds: The maximum amount of time to gather records before invoking the function.

• ScalingConfig: With only one property MaximumConcurrency limits the number of concurrent instances that the Amazon SQS event source can invoke.

Run sam build to build the application, and then sam deploy --guided to deploy it.

SNS

Main features:

• SNS invokes the function asynchronously.

• Batching is not available, messages are delivered one by one.

• On errors, the event is lost unless DLQ is configured in the function.

Create a Lambda function to handle SNS events running the following command:

dotnet new lambda.SNS -n SNSTrigger -o .

Create a template.yaml file with the following content:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  SNS

Globals:
  Function:
    Timeout: 15
    MemorySize: 512
    Runtime: dotnet6
    Architectures:
      - x86_64

Resources:
  SNSTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: "mySNSTopic"

  SNSFunction:
    Type: AWS::Serverless::Function
    Properties:
      Runtime: dotnet6
      Handler: SNSTrigger::SNSTrigger.Function::FunctionHandler
      CodeUri: ./src/SNSTrigger/
      Events:
        SNSEvent:
          Type: SNS
          Properties:
            Topic: !Ref SNSTopic

Outputs:
  SNSConsumerFunction:
    Description: SNS consumer function name
    Value: !Ref SNSFunction

The event type SNS has the following properties:

• Topic: The ARN of the topic to subscribe to.

• RedrivePolicy: Sends undeliverable messages to the specified Amazon SQS dead-letter queue.

    {
      "deadLetterTargetArn": "arn:aws:sqs:us-east 2:123456789012:MyDeadLetterQueue"
    }
  

• FilterPolicy: Enables the subscriber to filter out unwanted messages.

• SqsSubscription: Enable batching SNS topic notifications in an SQS queue.

Run sam build to build the application and then sam deploy --guided to deploy it.

SNS to SQS

There are several advantages to having an SQS between SNS and Lambda, especially when you do not want to lose any messages or reprocess them in case of failures. Therefore, you can change the template.yaml above with:

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31
Description: >
  SNS to SQS

Globals:
  Function:
    Timeout: 15
    MemorySize: 512
    Runtime: dotnet6
    Architectures:
      - x86_64

Resources:
  SQSSubscriptionQueue:
    Type: AWS::SQS::Queue
    Properties:
      QueueName: "mySubscriptionSQSQueue"

  SNSTopic:
    Type: AWS::SNS::Topic
    Properties:
      TopicName: "mySNSTopic"

  SNSFunction:
    Type: AWS::Serverless::Function
    Properties:
      Runtime: dotnet6
      Handler: SNSTrigger::SNSTrigger.Function::FunctionHandler
      CodeUri: ./src/SNSTrigger/
      Events:
        SNSEvent:
          Type: SNS
          Properties:
            Topic: !Ref SNSTopic
            SqsSubscription:
              BatchSize: 10
              QueueArn: !GetAtt SQSSubscriptionQueue.Arn
              QueueUrl: !Ref SQSSubscriptionQueue
              Enabled: true

Outputs:
  SNSConsumerFunction:
    Description: SNS consumer function name
    Value: !Ref SNSFunction

Thanks, and happy coding.