We allow customers to attach their own ISO to virtual machines using direct download links over HTTP/HTTPS. As long as you have your ISO hosted on a publicly available web server, with a direct download link, you can attach it to your server easily in one-click.
At ExtraVM we provide mountable Netboot.xyz ISO which lets you network install any common Linux operating systems, liveCD images, rescue systems, and more. You can read about Netboot.xyz at the link below.
If you prefer to do a manual install of an operating system over VNC, we highly recommend using the Netboot.xyz installer.