Introduction

AWS Lambda is a serverless compute service that allows developers to run code in response to events without having to manage server infrastructure. One powerful feature of AWS Lambda is the ability to trigger functions on a scheduled basis using CloudWatch Events or EventBridge. AWS CloudFormation offers the ability to define and provision AWS infrastructure as code, including setting up scheduled event sources for AWS Lambda functions.

Understanding Scheduled Event Sources in AWS Lambda

Scheduled events enable Lambda functions to run at specified intervals, similar to the functionality of cron jobs. This can be immensely useful for automating routine checks, batch processing, cleanup jobs, and more.

Cron and Rate Expressions

AWS supports two types of expressions to set up scheduling:

1. Rate Expressions: Define frequencies in terms of fixed units like minutes, hours, or days. For example, `rate(5 minutes)` signifies a trigger every five minutes.
2. Cron Expressions: Offer complex schedules using a format similar to Unix cron syntax. For example, `cron(0/15 * * * ? *)` triggers every 15 minutes.

CloudFormation Support for Scheduled Events

Using AWS CloudFormation, you can define and automate the creation of AWS resources including the setup of scheduled events for AWS Lambda functions. Below is a technical example demonstrating how to implement a scheduled event source using CloudFormation.

CloudFormation Template

Here's a step-by-step explanation and example template for setting up a scheduled event source for an AWS Lambda function using AWS CloudFormation:

• Arn: !GetAtt MyLambdaFunction.Arn
• Lambda Function: The resource `MyLambdaFunction` defines the Lambda function's properties, such as its handler, execution role, and the location of the code in S3.
• Event Rule: The `MyEventRule` resource specifies an EventBridge (previously CloudWatch Events) rule. The `ScheduleExpression` defines a rate of one hour for executing the function.
• Permission: The `PermissionForEventsToInvokeLambda` resource grants EventBridge permission to trigger the Lambda function, which is essential for the rule to function effectively.