Cloud-init is a tool that runs automatically the first time a virtual machine or cloud server starts up. Its job is to configure the new machine based on instructions provided at launch, so the system arrives in a usable state without a human logging in and doing it manually. When a server boots on a cloud platform like AWS, Azure, or Google Cloud, cloud-init reads setup instructions from two sources. The first is metadata provided by the cloud platform itself, such as the hostname or network configuration. The second is optional user data, which is a script or configuration file you supply when launching the instance. Cloud-init processes these instructions and carries out tasks like setting up network interfaces, configuring storage, installing packages, creating user accounts, and placing SSH keys so you can log in securely. The tool is described as the industry-standard approach for this kind of first-boot setup. It ships by default in most major Linux distributions and is supported by virtually all public cloud providers as well as private cloud systems. Because it speaks a common format, the same user-data configuration file can work across different cloud platforms and Linux distributions without modification. The project is maintained by Canonical, the company behind Ubuntu, but it is not Ubuntu-specific. The README links to documentation covering supported clouds, supported distributions, and a contributing guide for developers who want to help with the code. The README itself is brief, as most of the detail lives in the external documentation site at docs.cloud-init.io.
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