Use Terraform to set up a Lambda function triggered by a scheduled event source

AWS Lambda functions can be triggered by scheduled events, such as cron jobs, using Amazon EventBridge (formerly CloudWatch Events). Terraform makes it easy to set up this integration.

Prerequisites

• An AWS account with appropriate permissions.
• Terraform installed on your system.

Steps to Set Up a Lambda Function with a Scheduled Event

Step 1: Write the Lambda Function Code

Create a simple Python script for the Lambda function. Save it as lambda_function.py:

def lambda_handler(event, context):
    print("Scheduled event triggered")
    return {
        'statusCode': 200,
        'body': 'Success'
    }

Step 2: Create a Terraform Configuration

Define the resources needed for the Lambda function and the scheduled event.

resource "aws_iam_role" "lambda_role" {
  name = "lambda_execution_role"

  assume_role_policy = jsonencode({
    Version = "2012-10-17",
    Statement = [
      {
        Action = "sts:AssumeRole",
        Effect = "Allow",
        Principal = {
          Service = "lambda.amazonaws.com"
        }
      }
    ]
  })
}

resource "aws_iam_role_policy_attachment" "lambda_policy" {
  role       = aws_iam_role.lambda_role.name
  policy_arn = "arn:aws:iam::aws:policy/service-role/AWSLambdaBasicExecutionRole"
}

resource "aws_lambda_function" "example" {
  filename         = "lambda_function.zip"
  function_name    = "example_lambda"
  role             = aws_iam_role.lambda_role.arn
  handler          = "lambda_function.lambda_handler"
  runtime          = "python3.9"
  source_code_hash = filebase64sha256("lambda_function.zip")
}

resource "aws_cloudwatch_event_rule" "schedule" {
  name                = "example-schedule"
  schedule_expression = "rate(5 minutes)"
}

resource "aws_cloudwatch_event_target" "lambda_target" {
  rule      = aws_cloudwatch_event_rule.schedule.name
  target_id = "lambda"
  arn       = aws_lambda_function.example.arn
}

resource "aws_lambda_permission" "allow_cloudwatch" {
  statement_id  = "AllowExecutionFromCloudWatch"
  action        = "lambda:InvokeFunction"
  function_name = aws_lambda_function.example.function_name
  principal     = "events.amazonaws.com"
  source_arn    = aws_cloudwatch_event_rule.schedule.arn
}

Step 3: Deploy the Configuration

1. Zip the Lambda function code:

   zip lambda_function.zip lambda_function.py
   

2. Initialize Terraform:

   terraform init
   

3. Apply the configuration:

   terraform apply
   

Step 4: Verify the Setup

Check the AWS Management Console to ensure the Lambda function and scheduled event are set up correctly. The function should trigger every 5 minutes.

Best Practices

• Use environment variables to configure your Lambda function dynamically.
• Monitor your Lambda function with Amazon CloudWatch Logs.
• Use Terraform modules to organize your code for reusability.

By following these steps, you can efficiently set up a Lambda function triggered by a scheduled event using Terraform.