Terraform Lambda Event Template Creation

• Introduction
• Step-by-Step Guide
• Code Example
• Additional Notes
• Summary
• Conclusion
• References

While Terraform doesn't directly support creating Lambda test events within the aws_lambda_function resource, you can achieve this through a workaround using local files and the file function. This approach involves defining your test event in a JSON file, reading the file content using Terraform's file function, and then passing the content as an environment variable to your Lambda function resource.

While Terraform doesn't directly support creating Lambda test events within the aws_lambda_function resource, you can achieve this through a workaround using local files and the file function.

1. Define your test event in a JSON file:

   {
     "key1": "value1",
     "key2": "value2"
   }

2. Read the JSON file content using file function:

   locals {
     test_event = file("path/to/test_event.json")
   }

3. Pass the test_event variable to your Lambda function resource:

   resource "aws_lambda_function" "example" {
     # ... other configurations ...
   
     environment {
       variables = {
         TEST_EVENT = local.test_event
       }
     }
   }

This approach allows you to store test events in separate files and manage them through your version control system. Your Lambda function can then access these events via environment variables.

Remember that this method injects the entire event data into an environment variable. For larger events, consider using alternative approaches like storing the event in an S3 bucket and passing the bucket/object key to your Lambda function.

This code defines infrastructure using Terraform to create an AWS Lambda function and its dependencies. It sets up an IAM role for the function, reads a test event from a local JSON file, and configures the Lambda function to receive this test event as an environment variable. The code also includes instructions for creating a zip archive of the Lambda function code and deploying the entire setup using Terraform.

1. Create a directory for your Lambda function and navigate to it:

mkdir my-lambda-function
cd my-lambda-function

2. Create a file named test_event.json inside the directory and add your test event data:

{
  "key1": "value1",
  "key2": "value2"
}

3. Create a file named main.tf and add the following Terraform code:

terraform {
  required_providers {
    aws = {
      source  = "hashicorp/aws"
      version = "~> 4.0"
    }
  }
}

# Configure the AWS provider
provider "aws" {
  region = "us-east-1" # Replace with your desired region
}

# Read the test event from the JSON file
locals {
  test_event = file("test_event.json")
}

# Create a Lambda function
resource "aws_lambda_function" "example" {
  function_name = "my-lambda-function"
  runtime       = "nodejs16.x" # Replace with your desired runtime
  handler       = "index.handler" # Replace with your handler function

  # Define an inline function for demonstration purposes
  source_code_hash = data.archive_file.zip.output_base64sha256
  role             = aws_iam_role.lambda_exec.arn

  # Pass the test event as an environment variable
  environment {
    variables = {
      TEST_EVENT = local.test_event
    }
  }
}

# Create a zip archive of the Lambda function code
data "archive_file" "zip" {
  type        = "zip"
  source_dir = "./lambda_code" # Replace with your actual code directory
  output_path = "lambda_function.zip"
}

# Create an IAM role for the Lambda function
resource "aws_iam_role" "lambda_exec" {
  name = "lambda_exec_role"

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

4. Create a directory named lambda_code and add your Lambda function code (e.g., index.js):

// lambda_code/index.js
exports.handler = async (event) => {
  // Access the test event from the environment variable
  const testEvent = JSON.parse(process.env.TEST_EVENT);

  // Your Lambda function logic here...
  console.log("Test Event:", testEvent);

  return {
    statusCode: 200,
    body: JSON.stringify({ message: "Success!" }),
  };
};

5. Run Terraform to deploy your Lambda function:

terraform init
terraform apply

This will create a Lambda function with your specified configuration and inject the content of test_event.json into the TEST_EVENT environment variable. Your Lambda function can then access and utilize this test event data.

Remember to replace the placeholder values in the code with your actual configuration details.

• Security: Be mindful of storing sensitive data in test events. Avoid putting secrets directly in these files. Consider using environment variables or AWS Secrets Manager for sensitive information.
• Alternative for Large Events: For larger test events, directly injecting into environment variables can hit size limits. Consider:
  • S3: Store the event in an S3 bucket and pass the bucket name and object key to your Lambda function.
  • API Gateway: If invoking via API Gateway, pass the event in the request body.
• Testing Frameworks: This approach is primarily for basic testing during deployment. For more comprehensive testing, explore frameworks like:
  • AWS SAM: Offers local testing and event simulation.
  • Jest: Popular JavaScript testing framework that can be used with Lambda.
• Version Control: Store your test event JSON files in version control alongside your Terraform code to track changes and ensure consistency across environments.
• Organization: For multiple Lambda functions, consider organizing test events into subdirectories or using a naming convention to maintain clarity.
• Dynamic Events: While this example uses a static JSON file, you can generate dynamic event data using Terraform's templating features or external scripts if needed.
• Lambda Layers: If you have common test event structures, consider packaging them into a Lambda Layer for reuse across multiple functions.

This article outlines a workaround for creating Lambda test events in Terraform, as direct support is not available.

Method:

1. Store Test Event: Define your test event data in a JSON file.
2. Read with Terraform: Utilize the file function within a locals block to read the JSON file's content and store it in a variable.
3. Pass as Environment Variable: Include the variable containing the test event data within the environment block of your aws_lambda_function resource.

Benefits:

• Manage test events through version control alongside your Terraform code.
• Access test events within your Lambda function via environment variables.

Considerations:

• This method might not be suitable for large event data due to environment variable size limitations.
• For larger events, consider storing them in an S3 bucket and passing the bucket/object key to your Lambda function.

In conclusion, while Terraform doesn't offer a built-in way to define Lambda test events directly, the workaround using local JSON files and the file function provides a practical solution. This method allows for version-controlled management of test events and easy integration with your Lambda function deployments. However, be mindful of the limitations regarding environment variable sizes and consider alternative approaches like S3 for larger test events. Remember to prioritize security by avoiding storing sensitive information directly in these files and explore testing frameworks for more comprehensive testing scenarios. By understanding these aspects, you can effectively leverage Terraform to manage your Lambda test events and streamline your serverless application development workflow.

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