cfn inti and signal

cfn-init

• The script must be called from user data
• takes in stack id, region, instance
• You’ll need to give AWS::Cloudformation::Init content in the metadata section

---
Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      AvailabilityZone: us-east-1a
      ImageId: ami-0a3c3a20c09d6f377
      InstanceType: t2.micro
      SecurityGroups:
        - !Ref SSHSecurityGroup
      # we install our web server with user data
      UserData: 
        Fn::Base64:
          !Sub |
            #!/bin/bash -xe
            # Get the latest CloudFormation package
            dnf update -y aws-cfn-bootstrap
            # Start cfn-init
            /opt/aws/bin/cfn-init -s ${AWS::StackId} -r MyInstance --region ${AWS::Region} || error_exit 'Failed to run cfn-init'
    Metadata:
      Comment: Install a simple Apache HTTP page
      AWS::CloudFormation::Init:
        config:
          packages:
            yum:
              httpd: []
          files:
            "/var/www/html/index.html":
              content: |
                <h1>Hello World from EC2 instance!</h1>
                <p>This was created using cfn-init</p>
              mode: '000644'
          commands:
            hello:
              command: "echo 'hello world'"
          services:
            sysvinit:
              httpd:
                enabled: 'true'
                ensureRunning: 'true'
 
  # our EC2 security group
  SSHSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: SSH and HTTP
      SecurityGroupIngress:
      - CidrIp: 0.0.0.0/0
        FromPort: 22
        IpProtocol: tcp
        ToPort: 22
      - CidrIp: 0.0.0.0/0
        FromPort: 80
        IpProtocol: tcp
        ToPort: 80
 

cfn-Signal

• Need to be invoked in the user-data script
• Takes in stack name, resource as wait condition, region and an exit code which you pass the previous commands exit code or anything of your wish
• Needs a resource of type AWS::CloudFormation::Waticondition with appropirate properties
• There are two things for reporting

  • Waitcondition

  • resource singaling

---
Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Properties:
      AvailabilityZone: us-east-1a
      ImageId: ami-0a3c3a20c09d6f377
      InstanceType: t2.micro
      SecurityGroups:
        - !Ref SSHSecurityGroup
      # we install our web server with user data
      UserData: 
        Fn::Base64:
          !Sub |
            #!/bin/bash -x
            # Get the latest CloudFormation package
            dnf update -y aws-cfn-bootstrap
            # Initialize EC2 Instance
            /opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource MyInstance --region ${AWS::Region}
            # Get result of last command
            INIT_STATUS=$?
            # send result back using cfn-signal
            /opt/aws/bin/cfn-signal -e $INIT_STATUS --stack ${AWS::StackName} --resource SampleWaitCondition --region ${AWS::Region}
            # exit the script
            exit $INIT_STATUS
    Metadata:
      Comment: Install a simple Apache HTTP page
      AWS::CloudFormation::Init:
        config:
          packages:
            yum:
              httpd: []
          files:
            "/var/www/html/index.html":
              content: |
                <h1>Hello World from EC2 instance!</h1>
                <p>This was created using cfn-init</p>
              mode: '000644'
          commands:
            hello:
              command: "echo 'boom' && exit 1"
          services:
            sysvinit:
              httpd:
                enabled: 'true'
                ensureRunning: 'true'

  SampleWaitCondition:
    CreationPolicy:
      ResourceSignal:
        Timeout: PT3M
        Count: 1
    Type: AWS::CloudFormation::WaitCondition

  # our EC2 security group
  SSHSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: SSH and HTTP
      SecurityGroupIngress:
      - CidrIp: 0.0.0.0/0
        FromPort: 22
        IpProtocol: tcp
        ToPort: 22
      - CidrIp: 0.0.0.0/0
        FromPort: 80
        IpProtocol: tcp
        ToPort: 80