Cloud-init is a tool used in OpenStack to configure and initialize virtual machines (VMs) running in the cloud. It allows users to customize and automate the initial setup of their VMs, including configuring network interfaces, setting up users and SSH keys, running scripts and commands, and more.
Cloud-init uses a YAML-based configuration file called user-data, which contains instructions on how to configure the VM. The user-data file can be provided when launching a new instance or injected into an existing instance.
When a VM boots, the cloud-init software running inside the VM reads the user-data file and performs the necessary actions to configure the VM based on the specified instructions. This allows for quick and automated provisioning of VMs, as well as consistent configuration across multiple instances.
Some common use cases for cloud-init in OpenStack are:
Setting up network interfaces and IP addresses
Adding SSH keys to enable remote access
Running scripts or commands during instance launch
Installing and configuring software packages
Configuring user accounts and passwords
Overall, cloud-init simplifies the process of customizing and configuring VMs in OpenStack, allowing for faster deployment and easier management of cloud infrastructure.