Infrastructure as Code Testing

Infrastructure as Code Testing validates that infrastructure provisioning and configuration, managed as code, functions correctly, securely, and meets desired specifications before deployment.

Detailed explanation

Infrastructure as Code (IaC) has revolutionized how we manage and provision infrastructure. Instead of manually configuring servers and networks, we define infrastructure using code, allowing for automation, version control, and repeatability. However, just like any other code, IaC needs rigorous testing to ensure it behaves as expected and doesn't introduce vulnerabilities or misconfigurations. Infrastructure as Code Testing is the process of validating IaC code to ensure it provisions and configures infrastructure correctly, securely, and efficiently.

Why is IaC Testing Important?

Without proper testing, IaC can lead to several problems:

  • Configuration Drift: Inconsistencies between the intended infrastructure state (defined in the code) and the actual deployed infrastructure. This can lead to unpredictable behavior and failures.
  • Security Vulnerabilities: Misconfigured security groups, open ports, or insecure credentials can expose infrastructure to attacks.
  • Compliance Issues: Failure to adhere to regulatory requirements can result in fines and legal repercussions.
  • Downtime: Incorrect infrastructure provisioning can lead to application outages and business disruption.
  • Cost Overruns: Inefficient resource allocation or misconfigured scaling policies can result in unnecessary expenses.

Types of IaC Tests

Several types of tests can be performed on IaC code:

  • Static Analysis: This involves analyzing the code for syntax errors, style violations, and potential security vulnerabilities without actually executing it. Tools like yamllint for YAML files and terraform fmt for Terraform configurations can be used for static analysis.

    yamllint my_terraform_config.tf
terraform fmt my_terraform_terraform_config.tf

  • Unit Tests: These tests focus on individual modules or components of the IaC code. For example, you might unit test a Terraform module that creates a security group to ensure it allows the correct ports and protocols. Frameworks like Terratest are commonly used for unit testing Terraform code.

    package test
 
import (
	"testing"
 
	"github.com/gruntwork-io/terratest/modules/terraform"
	"github.com/stretchr/testify/assert"
)
 
func TestTerraformSecurityGroup(t *testing.T) {
	t.Parallel()
 
	terraformOptions := &terraform.Options{
		TerraformDir: "../examples/security-group",
	}
 
	defer terraform.Destroy(t, terraformOptions)
 
	terraform.InitAndApply(t, terraformOptions)
 
 // Example assertion: Check if the security group has the correct name
	securityGroupName := terraform.Output(t, terraformOptions, "security_group_name")
	assert.Equal(t, "example-security-group", securityGroupName)
}

  • Integration Tests: These tests verify that different components of the infrastructure work together correctly. For instance, you might test that a web server can communicate with a database server provisioned by the IaC code.

  • End-to-End Tests: These tests simulate real-world scenarios to ensure the entire infrastructure functions as expected. This might involve deploying an application to the provisioned infrastructure and testing its functionality.

  • Compliance Tests: These tests ensure that the infrastructure adheres to specific security and regulatory requirements. Tools like InSpec can be used to define and run compliance tests.

    control 'ssh-1.0' do
  impact 1.0
  title 'Verify SSH is properly configured'
  desc 'Ensures SSH is configured securely'
 
  describe service('ssh') do
    it { should be_installed }
    it { should be_enabled }
    it { should be_running }
  end
 
  describe port(22) do
    it { should be_listening }
    its('protocols') { should include('tcp') }
  end
end

  • Idempotence Tests: Idempotence means that applying the same IaC code multiple times should result in the same infrastructure state. These tests verify that the IaC code is idempotent and doesn't create duplicate resources or unexpected changes.

Best Practices for IaC Testing

  • Treat IaC as Code: Apply the same software development best practices to IaC as you would to application code, including version control, code reviews, and automated testing.
  • Automate Testing: Integrate IaC testing into your CI/CD pipeline to ensure that every change is thoroughly tested before deployment.
  • Use a Testing Framework: Leverage testing frameworks like Terratest or InSpec to simplify the process of writing and running tests.
  • Test Early and Often: Start testing early in the development process and run tests frequently to catch issues before they become major problems.
  • Define Clear Test Cases: Create well-defined test cases that cover different aspects of the infrastructure, including functionality, security, and compliance.
  • Use Mocking and Stubs: When testing individual components, use mocking and stubs to isolate them from external dependencies.
  • Monitor Infrastructure: Continuously monitor the deployed infrastructure to detect configuration drift and other issues.
  • Implement Rollback Strategies: Have a plan for rolling back changes if a deployment fails or introduces problems.
  • Secure Credentials: Never hardcode credentials in IaC code. Use secrets management tools to securely store and retrieve sensitive information.

Common Tools for IaC Testing

  • Terratest: A Go library for testing Terraform, Packer, and other infrastructure tools.
  • InSpec: An open-source framework for automating compliance, security, and other policy requirements.
  • Kitchen: A tool for testing infrastructure code across different platforms.
  • Serverspec: A framework for writing tests to validate the state of servers.
  • Testinfra: A Python framework for testing infrastructure.
  • Cloud specific testing tools: AWS CloudFormation Guard, Azure Policy as Code.

Example: Testing a Terraform Module with Terratest

Let's say you have a Terraform module that creates an AWS EC2 instance. You can use Terratest to write a unit test that verifies the instance is created with the correct AMI, instance type, and tags.

package test
 
import (
	"testing"
 
	"github.com/gruntwork-io/terratest/modules/terraform"
	"github.com/stretchr/testify/assert"
)
 
func TestTerraformEC2Instance(t *testing.T) {
	t.Parallel()
 
	terraformOptions := &terraform.Options{
		TerraformDir: "../examples/ec2-instance",
		Vars: map[string]interface{}{
			"ami_id":      "ami-0c55b9928c5d81c1c", // Example AMI ID
			"instance_type": "t2.micro",
			"tags": map[string]string{
				"Name": "example-ec2-instance",
			},
		},
	}
 
	defer terraform.Destroy(t, terraformOptions)
 
	terraform.InitAndApply(t, terraformOptions)
 
	instanceID := terraform.Output(t, terraformOptions, "instance_id")
	assert.NotEmpty(t, instanceID)
 
 // Add more assertions to verify other properties of the EC2 instance
}

This test first defines the Terraform options, including the directory containing the Terraform code and any variables that need to be passed. It then initializes and applies the Terraform code, creating the EC2 instance. Finally, it asserts that the instance ID is not empty, indicating that the instance was created successfully. You can add more assertions to verify other properties of the EC2 instance, such as the AMI, instance type, and tags.

By implementing a comprehensive IaC testing strategy, you can ensure that your infrastructure is reliable, secure, and compliant, reducing the risk of costly errors and downtime.

Further reading

Related Terms

A/B Testing

Acceptance Testing

Accessibility Tester