Immutable Infrastructure: Creating Machine Images with Packer and Terraform

The Drift Vulnerability (Mutable Servers)

Deploying code to running servers using SSH scripts results in Configuration Drift—packages, dependencies, and settings diverge across servers, causing release bugs.

Immutable infrastructure solves this by packaging configurations into machine images, replacing servers completely on updates.

DevOps Guideline: Never patch running servers. Build a fresh machine image and replace instances on release.

The Tooling Pipeline: Packer and Terraform

In 2014, HashiCorp's release of Terraform combined with Packer simplifies image creation and infrastructure provisioning:

• ◆Packer: Automates the creation of identical VM images (like AWS AMIs) using json configuration templates.
• ◆Terraform: Declaratively defines cloud infrastructure (servers, load balancers, databases) as code files.

# Simple Terraform instance configuration in late 2014
resource "aws_instance" "web_server" {
  ami           = "ami-12345678" # Packer generated AMI
  instance_type = "t2.micro"
  
  tags = {
    Name = "ShivamWebNode"
  }
}

By coding infrastructure, teams provision configurations programmatically, minimizing release errors.