Terraform: How to perform integration tests

Integration testing plays a crucial role in the infrastructure as code (IAC) lifecycle, especially when utilizing Terraform to manage resources. It ensures that the entire system—comprising various resources and modules—works together seamlessly. In this tutorial, we’ll delve into how to perform integration tests on your Terraform configurations, moving from basic concepts to more advanced scenarios, complete with code examples.

Getting Started with Terraform Testing

Before diving into integration testing, it’s important to understand what it entails. Integration testing in the Terraform context involves deploying resources with Terraform code, then verifying if they work together as expected. This could include checking if a web server can connect to a database, or if security group rules allow for specific network traffic.

To get started, you’ll need the following prerequisites:

• Terraform installed
• An AWS account (for this example)
• Basic understanding of Terraform syntax and structure

Basic Integration Testing Example

Let’s kick things off with a simple testing scenario: deploying an AWS EC2 instance and validating its accessibility over SSH.

Step 1: Define Terraform Configuration

resource "aws_instance" "web" {
  ami           = "ami-123456"
  instance_type = "t2.micro"
}

Step 2: Deploy & Verify

Next, initialize Terraform, apply the configuration, and then use a testing tool like Inspect, rspec-terraform, or even a simple Bash script to verify SSH connectivity.

Step 3: Example Verification Script

#!/bin/bash
IP=$(terraform output -raw instance_ip)
ssh -o ConnectTimeout=10 "$IP" echo "Success!"

If the script returns “Success!”, your basic integration test passes.

Advanced Integration Testing

As your infrastructure grows in complexity, so do your integration testing needs. Let’s explore a scenario where you’re deploying an entire VPC, with subnets, an EC2 instance, and a database, then verifying connectivity and data flow.

Step 1: Terraform Configuration for VPC

module "vpc" {
  source  = "terraform-aws-modules/vpc/aws"
  version = "2.77.0"
  name    = "my-vpc"
  cidr    = "10.0.0.0/16"
  ...
}

Step 2: Set Up EC2 Instance and Database

Within the VPC module, include the Terraform code for an EC2 instance and a RDS database, ensuring they’re configured to communicate.

Step 3: Testing Connectivity

After deployment, use a test script or tool to verify that the EC2 instance can communicate with the RDS database, such as making a simple query or accessing a particular service.

Automating Terraform Tests

Manual tests can be time-consuming. As such, integrating your Terraform tests into a CI/CD pipeline can streamline the process. Tools like Terratest offer a framework for writing and automating tests in Go. Here’s a simple example:

package test

import (
    "testing"
    terraform "github.com/gruntwork-io/terratest/modules/terraform"
)

func TestMyTerraform(t *testing.T) {
    terraformOptions := &terraform.Options{
        TerraformDir: "/path/to/terraform/code",
    }

    defer terraform.Destroy(t, terraformOptions)
    terraform.InitAndApply(t, terraformOptions)

    // Add your verification code here
}

This Terratest example initiates and applies Terraform configurations, then tears them down post-test, making it perfect for integration tests in ephemeral environments.

Testing Best Practices

Few practices to consider for robust Terraform integration tests include:

• Ensure your tests are idempotent. They should clean up resources post-verification to prevent cost overrun and configuration drift.
• Utilize modules for reusable components, making your infrastructure easier to test and deploy.
• Incorporate randomness in resource names to allow parallel test executions without collision.

Conclusion

Integration testing is essential for verifying the functionality of complex Terraform deployments. Through incremental complexity, from basic network checks to fully automated testing frameworks like Terratest, you can ensure your infrastructure behaves as expected in a real-world environment. Embrace these practices to maintain robust, reliable, and repeatable infrastructure deployments.