Cloud-init is the industry standard multi-distribution method for cross-platform cloud instance initialization. It is supported across all major public cloud providers, provisioning systems for private cloud infrastructure, and bare-metal installations.
On instance boot, cloud-init will identify the cloud it is running on, read any provided metadata from the cloud, and initialize the system accordingly. This may involve setting up the network and storage devices, configuring SSH access keys, and setting up many other aspects of a system. Later, cloud-init will parse and process any optional user or vendor data that was passed to the instance.