A Comprehensive Guide to Mastering Terraform Lambda Modules

A Comprehensive Guide to Mastering Terraform Lambda Modules

Once upon a time, in the world of modern cloud infrastructure and serverless architecture, a DevOps team worked with an ever-growing business. The business had many applications that required automation and quick responses to various events. To handle this need efficiently, the team used AWS Lambda functions. However, deploying and managing multiple Lambda functions for different applications became challenging.

That’s when our hero – Terraform – entered the scene! With Terraform’s robust Infrastructure as Code (IaC) capabilities, the DevOps team could create reusable modules for their Lambda functions. This story will guide you through creating a Terraform module for a Lambda function step-by-step while discussing its advantages, limitations, and trade-offs.

What is Terraform?

Terraform is an open-source IaC tool that allows you to define your infrastructure using configuration files in HashiCorp Configuration Language (HCL). This enables teams to manage their infrastructure code as with application code—using version control systems and automated testing.

Why Use a Terraform Module?

Creating reusable modules in Terraform can provide several benefits:

  1. Consistency: Reusable modules ensure consistent configuration across different environments.
  2. Maintainability: Updating or modifying module configurations becomes easier since changes must only be made in one place.
  3. Efficiency: Developers can spend less time writing boilerplate code and more time focusing on business requirements.

You can learn more about Terraform Modules with our complete and deep tutorial.

Getting Started with Your First Lambda Module

To begin creating your first simple terraforming lambda module:

module "lambda_function" {
  source = "./modules/lambda"

  function_name = "my_lambda_function"
  handler       = "index.handler"
  runtime       = "nodejs14.x"

  environment_variables {


As you create more advanced modules, there might be some trade-offs to consider:

  1. Complexity: As the module grows in functionality, it may become difficult to maintain and use.
  2. Flexibility: Highly configurable modules can lead to over-engineering, making them less flexible for specific use cases.

Expanding Your Module from Simple to Complex

As your project requirements change and grow, you may need to expand your Terraform module’s capabilities. Let’s use an example of adding additional features, such as VPC support and deploying multiple Lambda functions within a single module.

module "lambda_function" {
  source = "./modules/lambda"

  # Required parameters
  function_name = "my_lambda_function"
  handler       = "index.handler"
  runtime       = "nodejs14.x"

  # Optional parameters (VPC support)
  vpc_config {
    security_group_ids = ["sg-12345678"]
    subnet_ids         = ["subnet-12345678", "subnet-87654321"]

  # Deploy multiple lambda functions with different configurations
  additional_lambdas = [
      function_name          = "additional_lambda_1"
      handler                = "index.additionalHandler1"
      environment_variables2 = { ... } // key-value pairs for env variables
      function_name         = "additional_lambda_2"
      handler               = "index.additionalHandler2"
      environment_variables3 ={...}// key-value pairs for env variables


Although Terraform offers many advantages, it also has some limitations:

  1. Provider-specific features: Some AWS Lambda features or settings may not be supported by the Terraform provider. In such cases, you might need to rely on AWS CloudFormation or custom scripts instead.
  2. State management: Managing Terraform state files can be challenging depending on your team’s workflow, especially with multiple team members working on the same infrastructure.


Despite some limitations, using Terraform for managing Lambda functions offers several advantages:

  1. Version control: Your infrastructure code can be stored and versioned alongside your application code.
  2. Reusability: You can create reusable modules for different applications and environments.
  3. Streamlined deployments: Deploying changes to Lambda functions becomes more efficient when managed through Terraform.

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Testing Your Lambda Module with Terratest

This section will explore how to test your custom Terraform Lambda module using an automated testing framework called Terratest. Terratest is a popular infrastructure testing library written in Go (Golang) that provides an easy-to-use interface for validating Terraform code against deployed resources. This ensures your infrastructure always works as expected and increases overall quality assurance.

Setting Up Your Test Environment

Before starting, you’ll need to have the following tools installed:

  1. Go: Install the latest version of Go from the official website.
  2. Terraform: Make sure you have installed the latest version of Terraform.

Next, create a new directory

inside your Terraform module folder to store your test files.

Writing the Test Code

Inside the tests directory, create a file named lambda_test.go. This file will contain our test functions written in Golang using Terratest’s built-in helpers.

First, import the necessary packages:

package tests

import (


Now, write a test function that performs these steps:

  1. Create unique names for AWS resources using random strings.
  2. Define terraform options containing input variables and settings.
  3. Run terraform init and terraform apply.
  4. Retrieve outputs from terraform and get AWS resources data.
  5. Verify if configured resources match desired values.
  6. Clean up by running terraform destroy.

Here’s a sample test function:

func TestTerraformLambdaModule(t *testing.T) {

	region := "us-west-2"
	functionName := fmt.Sprintf("test_lambda_%s", random.UniqueId())

	terraformOptions := &terraform.Options{
		TerraformDir: "../",
		Vars: map[string]interface{}{
			"function_name": functionName,
			"handler":       "index.handler",
			"runtime":       "nodejs14.x",
			"region":        region,
                        // Add any additional variables here
                        // ...
                EnvVars: map[string]string {
                  // Specify credential environment variables for AWS provider authentication
                  "AWS_DEFAULT_REGION": region,


	defer terraform.Destroy(t, terraformOptions)


After defining the test function, run terraform init and terraform apply:

terraform.InitAndApply(t, terraformOptions)

Now you can use Terratest assertions to validate the created resources. For example:

// Verify if the Lambda function was created successfully.
lambdaARN := aws.GetLambdaFunctionARN(t, region, functionName)
assert.NotNil(t, lambdaARN)

// Retrieve environment variables and validate their values.
lambdaEnvVars := aws.GetLambdaFunctionEnvironmentVariables(t, region, functionName)
assert.Equal(t, "some_value", lambdaEnvVars["SOME_ENVIRONMENT_VARIABLE"])

Running Your Tests

To execute your tests using Terratest, open a terminal window and navigate to the tests directory of your Terraform module.

Run this command to initiate testing:

go test -v -timeout 30m

Terratest will now start running your tests. If successful, you’ll see a message similar to this:

ok      path/to/your/tests   7.160s


In this tutorial, we’ve explored the process of creating, deploying, and testing a Terraform Lambda module for real-world projects. We delved into the benefits of working with reusable modules, discussed trade-offs and limitations, and demonstrated how to expand your module from a simple setup to more complex scenarios.

By diving deeper into advanced topics like automated testing using Terratest, you’ve comprehensively understood how to improve quality assurance within your infrastructure codebase. Implementing the methods discussed in this tutorial will streamline your DevOps processes and ensure consistency and maintainability throughout various projects.

As you continue your journey in modern cloud infrastructure and serverless architectures, remember that learning from real-world examples is invaluable. Keep embracing new tools like Terraform while adapting to ever-changing business requirements. With continuous learning and practice, you’ll become an expert in managing serverless resources efficiently and confidently tackle any challenges that come your way.

Happy terraforming!

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