What is cloud-init and how is it used in Azure?

Experience Level: Junior
Tags: Azure Cloud Azure Virtual Machines

Answer

cloud-init is a widely used approach to customize a Linux VM as it boots for the first time. You can use cloud-init to install packages and write files, or to configure users and security.

Because cloud-init is called during the initial boot process, there are no additional steps or required agents to apply your configuration. For more information on how to properly format your #cloud-config files or other inputs, see the cloud-init documentation site. #cloud-config files are text files encoded in base64.

cloud-init also works across distributions. For example, you don't use apt-get install or yum install to install a package. Instead you can define a list of packages to install. cloud-init automatically uses the native package management tool for the distro you select.

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.

Cloud instances are initialized from a disk image and instance data:

  • Cloud metadata
  • User data (optional)
  • Vendor data (optional)
cloud-init will identify the cloud it is running on during boot, read any provided metadata from the cloud and initialize the system accordingly. This may involve setting up the network and storage devices to configuring SSH access key and many other aspects of a system. Later on the cloud-init will also parse and process any optional user or vendor data that was passed to the instance.
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