Invoking an AWS Lambda Function from Another Lambda Function and Scheduling the Function

AWS Lambda allows you to run code without provisioning or managing servers. You can invoke one Lambda function from another and schedule Lambda functions using Amazon CloudWatch Events. In this blog post, we'll explore both processes.

Prerequisites

Before we start, ensure you have the following:

  • An AWS account
  • Basic knowledge of AWS Lambda and IAM roles
  • AWS CLI installed and configured

1. Invoking a Lambda Function from Another Lambda Function

To invoke a Lambda function from another Lambda function, follow these steps:

Step 1: Create the Lambda Functions

  1. Function A (Invoker): This function will invoke another Lambda function.



  2. Function B (Invoked): This function will be invoked by Function A.



Step 2: Set Up IAM Roles and Permissions

  • Create an IAM Role for Lambda with the following policies:

    • AWSLambdaBasicExecutionRole

    • Custom policy to allow lambda:InvokeFunction



  • Attach the IAM Role to both Lambda functions.

2. Scheduling a Lambda Function

To schedule a Lambda function using CloudWatch Events, follow these steps:

Step 1: Create a Lambda Function

Create a Lambda function (e.g., ScheduledFunction) that will be triggered on a schedule.






Step 2: Create a CloudWatch Events Rule

  1. Navigate to the CloudWatch console and select Rules.

  2. Create a new rule with the following settings:

    • Event Source: Event Source - Schedule
    • Schedule Expression: cron(0 12 * * ? *) (This expression schedules the function to run every day at 12 PM UTC).

  3. Add Target:

    • Target: Lambda function
    • Function: ScheduledFunction

  4. Configure Permissions: Ensure that the CloudWatch Events rule has permission to invoke the Lambda function. This can be done by adding a resource-based policy to the Lambda function.




Conclusion

In this blog post, we covered how to invoke an AWS Lambda function from another Lambda function and how to schedule a Lambda function using CloudWatch Events. These techniques can be useful for building serverless workflows and automating tasks in AWS.

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