Summary of CloudFormation Helper Scripts Training

• Problems with User Data:
  • Inflexibility with large instance configurations.
  • Difficulty in evolving EC2 instance state without termination.
  • Readability issues with user data scripts.
  • Uncertainty about the success of user data scripts.
• Solution: CloudFormation Helper Scripts:
  • Python scripts included with Amazon Linux AMIs or installable via yum or dnf.
  • Important scripts include cfn-init, cfn-signal, cfn-get-metadata, and cfn-hup.
• Focus on cfn-init:
  • Retrieves and interprets resource metadata.
  • Installs packages, creates files, and starts services on EC2 instances.
  • Makes complex EC2 configurations readable.
  • Logs are stored in /var/log/cfn-init.log.
• CloudFormation Init Block:
  • Part of the metadata block within a resource.
  • Components include packages, groups, users, sources, files, commands, and services.
• Example of cfn-init Usage:
  • EC2 instance queries CloudFormation service for init data.
  • User data script updates and runs cfn-init with StackId, resource name, and region.
  • Metadata block contains CloudFormation init block with configuration details.
  • Instance creation and configuration are more readable and manageable.
• Debugging and Logs:
  • Check /var/log/cloud-init.log for basic run information.
  • Detailed command output and errors are logged in /var/log/cfn-init.log and cfn-init-cmd.log.
• Cleanup:
  • Remember to delete the stack after the training.

Example Configuration in Markdown

Resources:
  MyInstance:
    Type: AWS::EC2::Instance
    Metadata:
      AWS::CloudFormation::Init:
        configSets:
          setup:
            - install_server
        install_server:
          packages:
            yum:
              httpd: []
          files:
            "/var/www/html/index.html":
              content: |
                Hello world!
              mode: 000644
              owner: root
              group: root
          services:
            sysvinit:
              httpd:
                enabled: true
                ensureRunning: true
    Properties:
      # ... other properties ...
      UserData:
        Fn::Base64: !Sub |
          #!/bin/bash -xe
          yum update -y aws-cfn-bootstrap
          /opt/aws/bin/cfn-init -v --stack ${AWS::StackName} --resource MyInstance --configsets setup --region ${AWS::Region}
          /opt/aws/bin/cfn-signal -e $? --stack ${AWS::StackName} --resource MyInstance --region ${AWS::Region}