DevSecOps in Practice

How Immutable Infrastructure Improves Security

In the next section, we will create the Kubernetes cluster. Since we want to focus on the DevOps and security aspects, we are going to use Terraform to create the cluster. In this way, we can automate the creation of the infrastructure and ensure that it is reproducible. Also, we can store the Terraform code in a version control system like Git to track changes and collaborate with other team members. Most importantly, Terraform (or OpenTofu) is an immutable infrastructure tool, which means, from a security perspective, it has more security advantages over mutable infrastructure. Let's explore how immutable infrastructure improves security. In the following sections, we will take a practical example to show how immutable infrastructure can bring more security to our infrastructure.

Eliminating Configuration Drift

Imagine you have two production servers running an application. In a mutable setup, administrators may manually update one server with a security patch but forget to apply it to the second server, leading to configuration drift. This inconsistency creates security gaps that attackers can exploit.

With immutable infrastructure as code tools, infrastructure is recreated from scratch with the latest configuration every time a change is needed. This guarantees that all instances are identical and fully patched, and as a result, eliminates the risk of an outdated or vulnerable machine running in production.

Example:

resource "aws_instance" "web" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = "t2.micro"
  user_data     = file("init.sh")
}

In this Terraform example, the aws_instance resource provisions a new EC2 instance with the latest AMI and user data script. This ensures that every deployment starts from a known good state and eliminates configuration drift.

### Reducing the Attack Surface for Persistent Threats

A developer manually updates an application on a traditional server but unknowingly leaves a **backdoor open**. This creates a long-lived security risk since the server is not automatically replaced or validated.

With Terraform, every deployment provisions a **new machine** instead of modifying the existing one. Any potential backdoor or compromised state does **not persist** because old instances are **destroyed and replaced** with secure, fresh instances. In an organization, security professionals, in collaboration with developers and operations teams, have to secure a model that is **immutable by design** and reproducible (secure once, deploy many times).

### Providing Faster Response to Vulnerabilities

A **zero-day vulnerability** is found in an outdated version of OpenSSL running on a cloud instance. In a **mutable** setup, an admin must manually update each affected server, which is time-consuming and error-prone.

Using Terraform, the infrastructure can be **redeployed with the latest patched version** within minutes. This provides a **faster response** to vulnerabilities and verifies that all instances are quickly secured without manual intervention.

**example:**

```hcl
resource "cluster" "example" {
  name    = "example"
  version = "1.21.3"
}

In this Terraform example, the cluster uses the version 1.21.3. If this version is vulnerable, it can be easily updated to the latest version by changing the version attribute and applying the Terraform configuration. Instead of manually updating each cluster and accumulating human errors (updates over time), the infrastructure is built from scratch with a new version.

Enforcing Security Compliance Automatically

An organization follows strict compliance policies (e.g., SOC 2, HIPAA). In a mutable setup, administrators must manually audit configurations and ensure compliance, which increases human error.

With Terraform (or its alternatives), compliance policies are enforced once in code (Infrastructure as Code - IaC). This guarantees continuous auditability and security enforcement. Since immutable infrastructure is reproducible, compliance checks can be automated and run at every deployment to ensure that the infrastructure is always compliant.

Preventing Unauthorized Modifications

A malicious insider or an attacker with stolen credentials modifies firewall rules to allow external access to a database. In a mutable environment, this change can go unnoticed for days or weeks.

Using infrastructure as code tools, administrators can create a continuous deployment pipeline that continuously enforces the desired state. An authorized change (e.g., modifying firewall rules) will be considered a drift from the desired state and reverted automatically on the next deployment (or even in real-time). Security policies, in this case, can be enforced programmatically.

Secure Software Updates and Rollbacks