cloud-init/CUSTOM.md

Custom Cloud Images

When creating a "cloud image" that is intended to be as dynamic as possible for various environments and custom deployments, there are several key considerations and components to include. Here's a summary of what's required:

1. Base Operating System

• Choose a minimal installation of a well-supported OS (e.g., Ubuntu, Debian, Fedora) that’s widely compatible with various cloud platforms.
• Strip down unnecessary packages to keep the image lightweight and reduce attack surfaces.

2. Cloud-Init Configuration

• Cloud-Init: This is the industry-standard tool for initializing cloud instances. It should be installed and properly configured in the image. Cloud-init allows for dynamic configuration of network settings, SSH keys, user data, hostname, and more when the image is deployed.
• Ensure that the cloud.cfg file is set up to handle common initialization tasks such as setting the hostname, user account creation, SSH key injection, and package installation.

3. Default User and SSH Configuration

• Default User: Set up a default user (e.g., ubuntu, debian, etc.) with sudo privileges. Ensure that this user can be easily overridden via cloud-init.
• SSH Key Injection: Ensure the image is configured to accept SSH keys through cloud-init or similar initialization systems to facilitate secure remote access.

4. Networking

• Dynamic Networking Configuration: Use DHCP for network configuration by default, but ensure that cloud-init can dynamically reconfigure network settings during initialization.
• No Hardcoded Network Configurations: Avoid hardcoding IP addresses or other network configurations to maintain flexibility.

5. Disk Partitioning

• Growable Partitions: Configure the disk partition to automatically resize on first boot to use all available disk space, ensuring that the image can be deployed on varying disk sizes without manual intervention.

6. Package Management and Updates

• Minimal Set of Packages: Include only essential packages and dependencies. This ensures that the image is lean and reduces potential attack vectors.
• Automatic Updates: Depending on your security posture, configure the image to apply security updates automatically. However, this should be easily overridden or managed by the user.

7. Security Configurations

• Disable Root Login: Ensure that root login via SSH is disabled by default to enhance security.
• Firewall and SELinux: Configure basic firewall rules and SELinux/AppArmor to enforce security policies out-of-the-box. However, these should be configurable during the deployment.

8. Customization Options

• Pre-Installed Tools: Depending on the use case, you might include pre-installed tools (e.g., monitoring agents, logging tools) that can be customized through cloud-init scripts.
• Custom Scripts: Allow for custom scripts to be run during the first boot, providing flexibility to install additional software or apply specific configurations as needed.

9. Testing and Validation

• Before distributing the image, thoroughly test it in various environments to ensure compatibility and functionality. This includes testing with different cloud-init configurations, network setups, and disk sizes.

10. Documentation

• Provide clear documentation that outlines how to use the image, including how to pass custom configurations via cloud-init, what defaults are set, and how users can modify the image for their needs.

Summary:

By following these guidelines, you can create a cloud image that is versatile, secure, and easy to use in a variety of cloud environments. The focus should be on ensuring that the image can be dynamically configured at deployment time, minimizing the need for manual intervention post-deployment.