Infrastructure as Code (IaC)

What Is IaC?

Infrastructure as Code (IaC) is the practice of defining and provisioning infrastructure (such as servers, storage, networking) using code. It can be done in two main styles:

• Declarative: Describe what the infrastructure should look like.
• Imperative: Write how to build it using real code.

Common Categories and Tools

Category	Tools	Language Used	Purpose
Declarative IaC	Terraform, CloudFormation	HCL, YAML, JSON	Define infrastructure as a desired state
Imperative IaC	AWS CDK, Pulumi	TypeScript, Python, etc.	Define and deploy infrastructure using real programming
Container Definition (not IaC itself)	Dockerfile, docker-compose	Docker syntax, YAML	Define app containers and services layout
Configuration Management	Ansible, Chef, Puppet	YAML, Ruby	Set up OS-level configurations

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Declarative vs. Imperative IaC

Aspect	Declarative	Imperative
You write...	What you want	How to achieve it
Tools	Terraform, CloudFormation	AWS CDK, Pulumi
Style	Configuration	Programming code
Analogy	"Build a 3 BHK house with garden"	"Lay bricks, install plumbing, then paint"
Flexibility	Limited, static	High, with loops, conditions, classes
Ease of use	Easier to read and manage	Easier to reuse and integrate with logic
Debugging	Less transparent	Easy to debug with standard tools

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Declarative IaC Example (Terraform)

resource "aws_s3_bucket" "my_bucket" {
  bucket = "my-cool-bucket"
  versioning {
    enabled = true
  }
}

• You describe the final outcome.
• Terraform figures out the steps to achieve it.

Pros:

• Simple and readable
• Great for managing large infra at scale
• Easy auditing and compliance

Cons:

• Limited logic (no loops, conditions without workarounds)

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Imperative IaC Example (AWS CDK, Pulumi)

const bucket = new s3.Bucket(this, 'MyBucket', {
  versioned: true,
});

• You write code that builds infrastructure.
• Supports logic, reuse, and integration with app pipelines.

Pros:

• Familiar to developers
• Flexible and reusable
• More automation-friendly

Cons:

• More complex for non-developers
• Slightly harder to audit visually

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Why Both Styles Exist

Use Case	Best Fit
Large-scale infra teams	Declarative (e.g., Terraform)
DevOps teams building infra with apps	Imperative (e.g., CDK, Pulumi)
Environments needing full visibility/compliance	Declarative
Code-based logic reuse	Imperative

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Tools That Mix Both

• AWS CDK generates CloudFormation templates, blending both styles.
• Pulumi uses imperative code but also tracks desired state like declarative tools.

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Quick Summary

Goal	Recommended Approach
Simplicity and visibility	Declarative (e.g., Terraform)
Logic and flexibility	Imperative (e.g., CDK, Pulumi)
Hybrid usage	Tools that support both (CDK, Pulumi)

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Related Terms and Concepts in IaC

Core Concepts

Term	Description
Provisioning	Automatically creating cloud resources
Declarative Configuration	Defines what infrastructure should exist
Imperative Configuration	Defines how to create infrastructure
Desired State	The target infrastructure configuration
Idempotency	Running code multiple times produces the same result
State Management	Tracks current vs. desired infrastructure state (e.g., Terraform .tfstate)

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Common IaC Tools

Tool	Type
Terraform	Declarative, multi-cloud
AWS CloudFormation	Declarative, AWS-only
AWS CDK	Imperative, AWS
Pulumi	Imperative, multi-cloud
Ansible	Declarative (mostly for config)
Chef / Puppet	Config management
Kubernetes YAML	Declarative (container infra)

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DevOps Practices Related to IaC

Practice	How It Relates to IaC
CI/CD	IaC is used to set up infra automatically in pipelines
GitOps	Infra code stored in Git and applied via automation
Immutable Infrastructure	Destroy and recreate infra instead of editing in-place
Blue-Green Deployment	Use IaC to switch traffic safely between environments
Rolling Update	Gradually deploy updates using IaC
Automated Testing	Infrastructure can be tested like application code

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Cloud Resources Commonly Managed by IaC

Cloud Component	Example Use via IaC
EC2 / Compute Engine / Azure VM	Create virtual machines
S3 / GCS / Blob Storage	Create storage buckets
VPC / Subnets / Route Tables	Define networking and connectivity
IAM Roles / Policies	Set up permissions and access control
RDS / DynamoDB / Cloud SQL	Provision managed databases
ECS / EKS / AKS	Set up container orchestration (including services, tasks, etc.)

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Supporting Concepts

Term	Description
Dockerfile	Describes how to build container images (used with IaC)
Container Orchestration	Kubernetes and IaC often used together
Secrets Management	IaC integrates with tools like AWS Secrets Manager, Vault
Monitoring and Logging	IaC can provision tools like CloudWatch, Datadog
Cost Optimization	IaC can define auto-scaling and shut down idle resources

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