CloudFormation & IaC

Duration: 60 min

Infrastructure as Code (IaC) lets you define AWS resources in code instead of clicking the console. AWS CloudFormation is the native IaC service. It uses JSON or YAML templates to create and manage stacks of resources. This module covers templates, stacks, parameters, outputs, and drift detection.

CloudFormation Basics

CloudFormation is AWS's IaC service. You write a template describing resources (EC2, S3, RDS, etc.), and CloudFormation creates and manages them as a stack.

Templates are JSON or YAML files. CloudFormation handles dependencies, rollback on failure, and updates.

Template Structure

A CloudFormation template has these sections:

AWSTemplateFormatVersion specifies the template version (usually "2010-09-09").

Description explains the template.

Parameters are input values you provide when creating the stack.

Resources define the AWS resources to create.

Outputs return values from the stack (e.g., instance IP, database endpoint).

Mappings define lookup tables for conditional values.

Stack Operations

Create a stack from a template. CloudFormation provisions all resources.

Update a stack to change resources. CloudFormation applies changes with minimal downtime.

Delete a stack to remove all resources (with some exceptions like S3 buckets with data).

Drift detection identifies resources that were manually changed outside CloudFormation.

Hands-On: Create CloudFormation Stack

Create a template file (template.yaml):

AWSTemplateFormatVersion: '2010-09-09'
Description: 'Simple EC2 instance'

Parameters:
  InstanceType:
    Type: String
    Default: t3.micro
    Description: EC2 instance type

Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: ami-0c55b159cbfafe1f0
      InstanceType: !Ref InstanceType
      Tags:
        - Key: Name
          Value: MyInstance

Outputs:
  InstanceId:
    Value: !Ref MyInstance
    Description: Instance ID
  InstancePublicIp:
    Value: !GetAtt MyInstance.PublicIp
    Description: Public IP address

Create the stack:

aws cloudformation create-stack --stack-name my-stack \
  --template-body file://template.yaml \
  --parameters ParameterKey=InstanceType,ParameterValue=t3.small

Describe stack:

aws cloudformation describe-stacks --stack-name my-stack

Get stack outputs:

aws cloudformation describe-stacks --stack-name my-stack \
  --query 'Stacks[0].Outputs'

Detect drift:

aws cloudformation detect-stack-drift --stack-name my-stack
aws cloudformation describe-stack-drift-detection-status \
  --stack-drift-detection-id drift-id

Python Boto3 Example

import boto3
import json

cf = boto3.client('cloudformation')

# Create stack
cf.create_stack(
    StackName='my-stack',
    TemplateBody=open('template.yaml').read(),
    Parameters=[
        {'ParameterKey': 'InstanceType', 'ParameterValue': 't3.micro'}
    ]
)

# Describe stack
response = cf.describe_stacks(StackName='my-stack')
for stack in response['Stacks']:
    print(f"Status: {stack['StackStatus']}")
    for output in stack.get('Outputs', []):
        print(f"{output['OutputKey']}: {output['OutputValue']}")

# Update stack
cf.update_stack(
    StackName='my-stack',
    TemplateBody=open('template.yaml').read()
)

# Delete stack
cf.delete_stack(StackName='my-stack')

Advanced Template Example

AWSTemplateFormatVersion: '2010-09-09'
Description: 'VPC with public and private subnets'

Parameters:
  VpcCidr:
    Type: String
    Default: 10.0.0.0/16

Resources:
  VPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: !Ref VpcCidr

  PublicSubnet:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: !Ref VPC
      CidrBlock: 10.0.1.0/24
      AvailabilityZone: us-east-1a

  InternetGateway:
    Type: AWS::EC2::InternetGateway

  AttachGateway:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      VpcId: !Ref VPC
      InternetGatewayId: !Ref InternetGateway

  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: !Ref VPC

  PublicRoute:
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: !Ref PublicRouteTable
      DestinationCidrBlock: 0.0.0.0/0
      GatewayId: !Ref InternetGateway

Outputs:
  VpcId:
    Value: !Ref VPC
  SubnetId:
    Value: !Ref PublicSubnet

Terraform Example

resource "aws_instance" "web" {
  ami           = "ami-0c55b159cbfafe1f0"
  instance_type = var.instance_type

  tags = {
    Name = "MyInstance"
  }
}

variable "instance_type" {
  type    = string
  default = "t3.micro"
}

output "instance_id" {
  value = aws_instance.web.id
}

output "public_ip" {
  value = aws_instance.web.public_ip
}

Quiz 1

Quiz 2

Quiz 3

Quiz 4

Quiz 5