AWS - CloudFormation

Theory

What is CloudFormation?

CloudFormation is a way to declare AWS infrastructure as code. You can create or delete AWS infrastructure resources that have been predefined in code. A similar service is Terraform, and these are collectively called IaC (Infrastructure as Code).

Template

A file that defines infrastructure resources to be created in code. JSON and YAML formats can be used.

Creation Order

Upload the template to CloudFormation
Execute the stack creation command in CloudFormation
AWS automatically creates resources in the order written in the template

Deletion Order

Execute the stack deletion command in CloudFormation
AWS automatically deletes the infrastructure resources

Hands-on Lab

Stack Creation

Parameters:
  KeyName:
    Description: Name of an existing EC2 KeyPair to enable SSH access to the instances. Linked to AWS Parameter
    Type: AWS::EC2::KeyPair::KeyName
    ConstraintDescription: must be the name of an existing EC2 KeyPair.
  LatestAmiId:
    Description: (DO NOT CHANGE)
    Type: "AWS::SSM::Parameter::Value<AWS::EC2::Image::Id>"
    Default: "/aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2"
    AllowedValues:
      - /aws/service/ami-amazon-linux-latest/amzn2-ami-hvm-x86_64-gp2

Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      ImageId: !Ref LatestAmiId
      InstanceType: t2.micro
      KeyName: !Ref KeyName
      Tags:
        - Key: Name
          Value: WebServer
      SecurityGroups:
        - !Ref MySG
      UserData:
        Fn::Base64: !Sub |
          #!/bin/bash
          yum install httpd -y
          systemctl start httpd && systemctl enable httpd
          echo "<h1>Test Web Server</h1>" > /var/www/html/index.html

  MySG:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Enable HTTP access via port 80 and SSH access via port 22
      SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 0.0.0.0/0
        - IpProtocol: tcp
          FromPort: 22
          ToPort: 22
          CidrIp: 0.0.0.0/0

Save the above code as test_lab1.yaml and proceed with the following steps

Access the CloudFormation Console and click Create stack
Select Prepared template -> Upload a template file
Specify an arbitrary stack name (CF-TEST)
KeyName: Select the key pair you are using

Verify Created Resources

Access the EC2 Console
Instances -> Instances
Check the WebServer instance IP
Verify SSH and HTTP access

Stack Deletion

Access the CloudFormation Console
Stacks tab
Select the created stack (CF-TEST)
Click Delete

Verify Deleted Resources

Access the EC2 Console
Instances -> Instances
Check the WebServer instance status (Terminated)

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