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.
