AWS CloudFormation

Name: cloud-formation
Rating: 88
Author: Tyler-R-Kendrick

Overview

CloudFormation is AWS's native IaC service for provisioning and managing AWS resources declaratively using JSON or YAML templates. Stacks are the unit of deployment — create, update, or delete all resources as a single unit.

Template Structure

yaml

AWSTemplateFormatVersion: "2010-09-09"
Description: "My application stack"

Parameters:
  Environment:
    Type: String
    Default: dev
    AllowedValues: [dev, staging, prod]

  InstanceType:
    Type: String
    Default: t3.micro

Resources:
  WebServer:
    Type: AWS::EC2::Instance
    Properties:
      InstanceType: !Ref InstanceType
      ImageId: ami-0abcdef1234567890
      Tags:
        - Key: Environment
          Value: !Ref Environment

  WebBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: !Sub "${AWS::StackName}-assets-${Environment}"

Outputs:
  InstanceId:
    Value: !Ref WebServer
    Export:
      Name: !Sub "${AWS::StackName}-InstanceId"

  BucketArn:
    Value: !GetAtt WebBucket.Arn

Key Intrinsic Functions

Function	Usage
`!Ref`	Reference a parameter or resource
`!Sub`	String substitution with variables
`!GetAtt`	Get an attribute of a resource
`!Join`	Join strings with a delimiter
`!Select`	Select from a list by index
`!If`	Conditional value
`!ImportValue`	Import from another stack's outputs

Stack Operations

bash

# Create a stack
aws cloudformation create-stack \
  --stack-name my-app \
  --template-body file://template.yaml \
  --parameters ParameterKey=Environment,ParameterValue=prod

# Preview changes
aws cloudformation create-change-set \
  --stack-name my-app \
  --change-set-name my-changes \
  --template-body file://template.yaml

# Update a stack
aws cloudformation update-stack \
  --stack-name my-app \
  --template-body file://template.yaml

# Delete a stack
aws cloudformation delete-stack --stack-name my-app

Nested Stacks

Break large templates into reusable components:

yaml

Resources:
  NetworkStack:
    Type: AWS::CloudFormation::Stack
    Properties:
      TemplateURL: https://s3.amazonaws.com/my-bucket/network.yaml
      Parameters:
        VpcCidr: "10.0.0.0/16"

  AppStack:
    Type: AWS::CloudFormation::Stack
    DependsOn: NetworkStack
    Properties:
      TemplateURL: https://s3.amazonaws.com/my-bucket/app.yaml
      Parameters:
        VpcId: !GetAtt NetworkStack.Outputs.VpcId

Best Practices

•Always use change sets to preview updates before applying.
•Use parameters and conditions to make templates reusable across environments.
•Enable termination protection on production stacks.
•Use DependsOn only when CloudFormation can't infer dependencies automatically.
•Export outputs for cross-stack references instead of hardcoding values.
•Use DeletionPolicy: Retain on stateful resources (databases, S3 buckets).
•Validate templates before deploying: aws cloudformation validate-template.