3: CloudFormation Helper Scripts

What are CF helper scripts?

• Python scripts to install software and start services on ec2 boxes
• Called directly from CF template
• Work with resource metadata defined in template
• Send signals back to the stack

cfn-init

• Retrieve and interpret resource metadata
• Install packages, create files, start services
• e.g. start web server

cfn-signal

• Signal between wait condition and the stack what’s going on
• Is the stack ready to continue build/update?
• Used with both wait conditions and creation policies

cfn-hup

• Continuously running daemon
• Checks for updates to metadata
• Executes custom hooks when changes detected
• Has an arg to make it run once then exit without daemon’ing

cfn-get-metadata

• Retrieve all metadata for a resource, or:
• Retrieve path to specific key or subtree of resource data
• Good for troubleshooting