Infrastructure as Code Patterns

IaC: infrastructure (servers, networks, databases) is described in code files that are versioned, reviewed, and applied automatically. This enables reproducibility, auditability, and treating infrastructure with the same rigor as application code.

Idempotent IaC: running terraform apply or ansible-playbook on already-converged infrastructure makes no changes. You can safely re-apply to fix drift or add resources without worrying about duplicating existing ones.

Configuration drift: when engineers make manual changes (hotfixes, console clicks) outside the IaC workflow, infrastructure diverges from the code. IaC tools detect and reconcile drift; drift also signals process problems.

Terraform state: Terraform stores the mapping between resource declarations and actual cloud resources (e.g., which aws_instance maps to i-1234). On plan, it compares current state to desired, showing what would change.

Declarative vs imperative: Terraform and Pulumi (declarative) say "I want 3 EC2 instances"; the tool calculates the diff. Ansible playbooks can be either; shell scripts are fully imperative. Declarative IaC is self-documenting and idempotent by nature.