Infrastructure as Code (IaC) Concepts Cheat Sheet
Summarizes core IaC principles including declarative vs imperative approaches, idempotency, state management, and drift detection.
1 PageBeginnerFeb 20, 2026
Core IaC Concepts
Foundational vocabulary shared across IaC tools.
- Declarative- You describe the desired end state; the tool figures out how to get there (Terraform, CloudFormation)
- Imperative- You specify the exact steps/commands to reach a state (shell scripts, older Chef recipes)
- Idempotency- Applying the same configuration repeatedly produces the same result without side effects
- State File- Record of the resources IaC currently manages and their real-world attributes
- Drift- When real infrastructure diverges from what's defined in code (e.g. manual console change)
- Plan/Diff- A dry-run showing what will change before applying, without modifying real resources
- Immutable Infrastructure- Servers are replaced rather than modified in place when a change is needed
IaC Tool Landscape
Common tools and where they fit.
- Terraform- Multi-cloud declarative provisioning using HCL, tracked via state files
- AWS CloudFormation- AWS-native declarative IaC using JSON/YAML templates
- Pulumi- Declarative infra defined using general-purpose languages (TypeScript, Python, Go)
- Ansible- Primarily configuration management, agentless, uses YAML playbooks
- AWS CDK- Defines CloudFormation stacks using imperative code that synthesizes to declarative templates
Minimal Terraform Example
Declarative resource definition demonstrating idempotent provisioning.
hcl
resource "aws_instance" "web" { ami = "ami-0abcdef1234567890" instance_type = "t3.micro" tags = { Name = "web-server" }}# terraform plan -> shows proposed changes# terraform apply -> reconciles real infra to match this file# terraform destroy -> tears down managed resources
Pro Tip
Never let engineers make manual console changes to IaC-managed resources — even small manual edits cause drift that silently gets reverted (or conflicts) on the next apply.
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