TripleO Style Guidelines

Element Specific Guidelines

Idempotency. A new version of metadata can be pushed at any time, for example due to a heat stack-update. Elements' os-refresh-config scripts must handle this gracefully. If they cannot be fully idempotent, they must fence their once-only sections.

For example, the keepalived element's configure.d script either reloads or restarts the service based on whether it appears to be already running. Another method of fencing would be to write a marker to ephemeral storage on first execution and skip once-only sections if the marker is present.