lambda-event-filtering

Lambda Event Filtering with DynamoDB and SQS

Key	Value
Services	Lambda, DynamoDB, SQS
Integrations	AWS SAM
Categories	Serverless; Event-Driven

Introduction

A demo application illustrating AWS Lambda event source filtering with DynamoDB and SQS using LocalStack. The sample uses AWS SAM and samlocal to deploy a Lambda function that is triggered only when SQS messages match specific filtering criteria defined on the DynamoDB stream.

Prerequisites

• A valid LocalStack for AWS license. Your license provides a LOCALSTACK_AUTH_TOKEN to activate LocalStack.
• Docker
• localstack CLI
• awslocal CLI
• samlocal — install with pip install aws-sam-cli-local
• Node.js with npm and ulid (npm install --save ulid)

Check prerequisites

make check

Installation

make install

Start LocalStack

export LOCALSTACK_AUTH_TOKEN=<your-auth-token>
make start

Deploy the Application

To set up the infrastructure on LocalStack for the first time, use the guided deploy (prompts for a stack name and confirmation):

samlocal deploy -g

Use the default options for the prompts and enter Y for the confirmation. For subsequent deploys after making changes:

samlocal deploy

Run the application

After deploying, send an SQS message to trigger the Lambda via the filter criteria:

awslocal sqs send-message \
    --queue-url http://localhost:4566/000000000000/MyQueue \
    --message-body '{"data": "A"}' \
    --delay-seconds 10

You will see a JSON output similar to the following:

{
    "MD5OfMessageBody": "64dfee8647a8264b25b01b7f22d72d3a",
    "MessageId": "22fbddd2-5add-4a03-a850-152780d786c1"
}

In the template.yaml we have defined the DynamoDB table and the Stream function with a filtering criteria. We instruct the Stream function to trigger the Lambda function only when the filtering criteria is satisfied.

Using the SQS, we send a message body to the DynamoDB stream to match the specific filtering criteria. After the message is sent, we can see the Lambda function being triggered and you can check the logs to verify it.

Destroy the application

samlocal delete

License

This code is available under the Apache 2.0 license.