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Learn how to effectively pass parameters to your Lambda function invoked by AWS CloudWatch events using custom input configurations.
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How to Pass Parameters to an AWS CloudWatch Event Target Lambda Function

When working with AWS services, especially when dealing with event-driven architectures, it’s common to need a way to pass parameters to your Lambda functions. One common scenario arises when setting up AWS CloudWatch events to trigger these functions. In this guide, we’ll dive into how to effectively pass parameters, specifically focusing on a use case with the alarmActions parameter.

The Challenge: Passing Parameters through CloudWatch Events

In many instances, you may need to notify your Lambda function with specific information when an event occurs. Suppose you have a CloudWatch event rule configured and you want to pass parameters directly to the target Lambda function. The challenge is to ensure that the parameters, like alarmActions, are correctly set in the CloudFormation template.

Consider the example CloudFormation template below, where LambdaInvokeScheduler triggers a Lambda function based on certain ECS events:

[[See Video to Reveal this Text or Code Snippet]]

While using the Input property as shown above, you may encounter difficulties in accessing this parameter in the Lambda function itself.

Solution: Correctly Accessing Parameters in Your Lambda Function

The key to resolving the issue lies in how you access these input parameters within your Lambda function. Initially, you might try to reference alarmActions directly as a function parameter. Here’s a simple example:

[[See Video to Reveal this Text or Code Snippet]]

While this may seem intuitive, it’s incorrect. The correct approach is to extract the value from the event object passed to the function. Here’s the modified code:

[[See Video to Reveal this Text or Code Snippet]]

Explanation of the Changes

Original Function Signature: The original attempt included alarmActions as a parameter, but this was not how the CloudWatch event triggers were designed to work.

Accessing the Parameter: By using event['alarmActions'], you tap directly into the data structure that the CloudWatch event generates, which contains all the parameters you defined, including alarmActions.

Conclusion

In summary, when working with AWS CloudWatch events and Lambda functions, it's essential to ensure you’re correctly passing and accessing parameters. Always keep in mind that input parameters should be extracted from the event object in your Lambda function.

By adopting this approach, you’ll be able to effectively pass any necessary parameters and ensure your Lambda functions operate as intended upon triggering from CloudWatch events. This not only enhances utility but also streamlines event-driven processes in your AWS environment.

If you have any questions or need further clarification, feel free to share in the comments below!