Demo Immutable Infrastructure With CloudFormation

#!/bin/bash
# For demo purposes, install and start a simple web server
yum install -y httpd
systemctl enable httpd
systemctl start httpd

# Create a simple page showing instance metadata
INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
AZ=$(curl -s http://169.254.169.254/latest/meta-data/placement/availability-zone)
VERSION="v1.0.0"

cat > /var/www/html/index.html << EOF
<html>
<head><title>Immutable Infrastructure Demo</title></head>
<body>
<h1>Immutable Infrastructure Demo</h1>
<p><strong>Instance ID:</strong> $INSTANCE_ID</p>
<p><strong>Availability Zone:</strong> $AZ</p>
<p><strong>Application Version:</strong> $VERSION</p>
<p><strong>Launch Template:</strong> devops-020-380-lt</p>
<hr>
<p>This instance was launched from a versioned launch template.</p>
<p>Updates deploy new AMI via instance refresh - no in-place changes.</p>
</body>
</html>
EOF

AWSTemplateFormatVersion: '2010-09-09'
Description: >
  Immutable Infrastructure Demo - Auto Scaling Group with Rolling Update
  and Launch Template versioning for Golden AMI deployments

Parameters:
  AMIId:
    Type: AWS::EC2::Image::Id
    Description: Golden AMI ID for application servers

  Environment:
    Type: String
    AllowedValues:
      - dev
      - test
      - prod
    Default: dev

  InstanceType:
    Type: String
    Default: t3.micro
    AllowedValues:
      - t3.micro
      - t3.small
      - t3.medium
      - t3.large
      - t3.xlarge

  VPCId:
    Type: AWS::EC2::VPC::Id
    Description: VPC for deployment

  PrivateSubnets:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Private subnets for Auto Scaling Group

  PublicSubnets:
    Type: List<AWS::EC2::Subnet::Id>
    Description: Public subnets for Load Balancer

  MinCapacity:
    Type: Number
  MaxCapacity:
    Type: Number
  DesiredCapacity:
    Type: Number

LaunchTemplate:
  Type: AWS::EC2::LaunchTemplate
  UpdateReplacePolicy: Retain
  DeletionPolicy: Delete
  Properties:
    LaunchTemplateName: !Sub '${AWS::StackName}-lt'
    VersionDescription: !Sub 'AMI: ${AMIId}'
    LaunchTemplateData:
      ImageId: !Ref AMIId
      InstanceType: !Ref InstanceType
      IamInstanceProfile:
        Arn: !GetAtt InstanceProfile.Arn
      SecurityGroupIds:
        - !Ref ApplicationSecurityGroup
      Monitoring:
        Enabled: true
      MetadataOptions:
        HttpTokens: required
        HttpPutResponseHopLimit: 1
        HttpEndpoint: enabled
      TagSpecifications:
        - ResourceType: instance
          Tags:
            - Key: Name
              Value: !Sub '${AWS::StackName}-instance'
            - Key: Environment
              Value: !Ref Environment
            - Key: AMI
              Value: !Ref AMIId

AutoScalingGroup:
  Type: AWS::AutoScaling::AutoScalingGroup
  Properties:
    AutoScalingGroupName: !Sub '${AWS::StackName}-asg'
    LaunchTemplate:
      LaunchTemplateId: !Ref LaunchTemplate
      Version: !GetAtt LaunchTemplate.LatestVersionNumber
    MinSize: !Ref MinCapacity
    MaxSize: !Ref MaxCapacity
    DesiredCapacity: !Ref DesiredCapacity
    HealthCheckType: ELB
    HealthCheckGracePeriod: 300
    TargetGroupARNs:
      - !Ref ApplicationTargetGroup
    VPCZoneIdentifier: !Ref PrivateSubnets
    TerminationPolicies:
      - OldestLaunchTemplate
      - OldestInstance
    Tags:
      - Key: Name
        Value: !Sub '${AWS::StackName}-asg'
        PropagateAtLaunch: false
      - Key: Environment
        Value: !Ref Environment
        PropagateAtLaunch: true

  UpdatePolicy:
    AutoScalingRollingUpdate:
      MinInstancesInService: !Ref MinCapacity
      MaxBatchSize: 2
      PauseTime: PT5M
      WaitOnResourceSignals: true
      SuspendProcesses:
        - HealthCheck
        - ReplaceUnhealthy
        - AZRebalance
        - AlarmNotification
        - ScheduledActions

  CreationPolicy:
    ResourceSignal:
      Count: !Ref DesiredCapacity
      Timeout: PT15M

ApplicationTargetGroup:
  Type: AWS::ElasticLoadBalancingV2::TargetGroup
  Properties:
    Name: !Sub '${AWS::StackName}-tg'
    Port: 80
    Protocol: HTTP
    VpcId: !Ref VPCId
    TargetType: instance
    HealthCheckEnabled: true
    HealthCheckPath: /
    HealthCheckProtocol: HTTP
    HealthCheckIntervalSeconds: 30
    HealthCheckTimeoutSeconds: 5
    HealthyThresholdCount: 2
    UnhealthyThresholdCount: 3
    Matcher:
      HttpCode: '200'
    Tags:
      - Key: Name
        Value: !Sub '${AWS::StackName}-tg'

HTTPListener:
  Type: AWS::ElasticLoadBalancingV2::Listener
  Properties:
    LoadBalancerArn: !Ref ApplicationLoadBalancer
    Port: 80
    Protocol: HTTP
    DefaultActions:
      - Type: forward
        TargetGroupArn: !Ref ApplicationTargetGroup

# Wait for httpd to respond on port 80
MAX_RETRIES=30
RETRY_COUNT=0

while [ $RETRY_COUNT -lt $MAX_RETRIES ]; do
    if [ "$(curl -s -o /dev/null -w '%{http_code}' http://localhost:80/)" = "200" ]; then
        echo "Application is healthy"
        break
    fi
    echo "Waiting for application... (attempt $RETRY_COUNT/$MAX_RETRIES)"
    sleep 10
    RETRY_COUNT=$((RETRY_COUNT + 1))
done

if [ $RETRY_COUNT -eq $MAX_RETRIES ]; then
    echo "Application health check failed"
    /opt/aws/bin/cfn-signal -e 1 \
        --stack "${AWS::StackName}" \
        --resource AutoScalingGroup \
        --region "${AWS::Region}"
    exit 1
fi

/opt/aws/bin/cfn-signal -e 0 \
    --stack "${AWS::StackName}" \
    --resource AutoScalingGroup \
    --region "${AWS::Region}"