cloud-init

cloud-init is the de facto standard for early initialization of cloud instances across major cloud providers including AWS, Azure, GCP, OpenStack, and others. It automates tasks like instance configuration, user setup, package installation, and running custom scripts during the first boot.

What cloud-init Does

cloud-init automates cloud VM provisioning by reading metadata and user-provided configuration, typically via user-data. Its key functions include:

  • Setting the hostname

  • Creating users and setting SSH keys

  • Installing packages

  • Configuring the network

  • Mounting volumes

  • Running arbitrary scripts or configuration management tools

Initialization Lifecycle

cloud-init executes in multiple stages:

  1. local – Reads instance metadata and configures low-level settings

  2. network – Waits for and verifies networking

  3. config – Applies configuration modules (user-data, package installs)

  4. final – Runs final scripts, reports status, and completes setup

Check status with:

cloud-init status --long

Key Directories and Files

Path
Description

/var/lib/cloud/

State and instance cache directory

/etc/cloud/cloud.cfg

Main configuration file

/etc/cloud/cloud.cfg.d/

Drop-in configuration fragments

/var/log/cloud-init.log

Main log file for debugging

/var/lib/cloud/instances/

Per-instance runtime data

Supported user-data Formats

cloud-init can process various data formats:

  • Shell script (must begin with #!/bin/bash or similar)

  • Cloud-config YAML (#cloud-config)

  • Multi-part MIME (combines scripts, cloud-config, etc.)

  • Include or Bootstrap formats (e.g., pointing to Ansible playbooks or remote URLs)

Example cloud-config

#cloud-config
hostname: example-vm
users:
  - name: devops
    groups: sudo
    sudo: ['ALL=(ALL) NOPASSWD:ALL']
    shell: /bin/bash
    ssh-authorized-keys:
      - ssh-rsa AAAAB3...

packages:
  - nginx
  - htop

runcmd:
  - systemctl start nginx
  - echo "Provisioning complete" > /home/devops/complete.txt

Useful Commands

Command
Description

cloud-init status

Check current status

cloud-init analyze

Analyze boot stages

cloud-init clean

Reset state and re-trigger on reboot

cloud-init single --file

Run a specific cloud-init module

cloud-init devel schema

Validate cloud-config YAML

Re-running cloud-init

To reinitialize cloud-init (e.g., after snapshotting or testing):

sudo cloud-init clean --logs

This clears all instance state from /var/lib/cloud.

Security Consideration

Avoid embedding passwords or sensitive credentials directly in user-data. Use encrypted secrets, external vaults, or secure boot-time provisioning mechanisms when possible.

Supported Environments

cloud-init is supported on:

  • AWS EC2

  • Microsoft Azure

  • Google Cloud Platform

  • OpenStack

  • Oracle Cloud

  • DigitalOcean

  • VMware (with customization)

  • LXC/LXD containers

  • Bare metal (via NoCloud or ISO seed images)

Adoption and Activity

GitHub (https://github.com/canonical/cloud-init):

  • Stars: ~2.6k

  • Open issues: ~160

  • Closed issues: 2.7k+

  • Primary Maintainer: Canonical (Ubuntu developers)

StackOverflow:

  • Approx. 1,500 questions under the cloud-init tag

  • Frequent topics: SSH key provisioning, cloud-config formatting, EC2 user-data, OpenStack instance customization

Let me know if you'd like to compare this with Ignition, kickstart, or Ansible cloud-init integration, or need help crafting complex multi-part MIME templates.

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