Proxmox Easy VMs
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How to Create a VM Template - PVE 9.1.2

Being able to have a ready to go image to fire VMs up is extremely useful for quick and easy to use sandboxes for isolated projects.

Creating Templates from an already existing VM is really easy from the proxmox's GUI. If, for instance, an ubuntu-server image is used to generate the VM, it can be just set to be a Template, but there are some things to take into account.

Problem - Duplicated IP

There's a catch, the machine-id, when using the template to create a cloned instance, the machine-id is duplicated, also the MAC address and consequently the IP address will not differ between instances.

A way of fixing this issue is by manually removing the machine-id (systemd - Is it OK to change /etc/machine-id? - Unix & Linux Stack Exchange) and then creating a template out of that instance:

rm -f /etc/machine-id && dbus-uuidgen --ensure=/etc/machine-id && rm /var/lib/dbus/machine-id && dbus-uuidgen --ensure

Then the cloned instance should regenerate the machine-id the first time it boots... Well, it doesn't, the instance cannot boot properly

A second approach would be changing the IP for each new clone, but it's an ugly solution and tedious to do.

With the ip a command we can get the network link associated with our ip address. In this case it's ens18.

So, using vim to write the config file:

sudo vim /etc/netplan/50-cloud-init.yaml

The following:

network:
  version: 2
  ethernets:
    ens18:
        dhcp4: false
        addresses:
          - 192.168.0.254/24
        nameservers:
          addresses:
            - 8.8.8.8
            - 8.8.4.4
        routes:
          - to: default
            via: 192.168.0.1

And applying the changes with:

sudo netplan apply

The static IP address should be set. Take into account that the router plays a big role in this, it may differ quite a lot. Ideally a sub network could be made for all the VM instances so the static IP addresses doesn't alter the "main" network.

It may work but it doesn't scale well. cloud-init gives more flexibility.

Solution - Cloud Init

To make it work, an ubuntu server vm can be created and configured with cloud-init or even simpler, an already created image can be used from Ubuntu Cloud Images. A QCow2 UEFI/GPT Bootable disk image is needed, it can be downloaded from the proxmox's GUI with Download from URL button (Also the sha256sum can be validated with the same tool)

Then, to create the template the docs have a dedicated section: Cloud-Init Support - Proxmox VE. There are some extra tweaks that may be worth mentioning:

  • Set the CPU to host.
  • Set the disk to SSD emulation (if an SSD is being used).
  • Enlarge the template's boot disk, by doing so the cloned instances will have more disk available with no extra steps.
  • Set the cloud-init file, the user, password, enable dhcp and set the ssh-keys of the PCs that need to access the VM.

There is an excellent video tutorial that explains the steps from the documentation in detail: Use Proxmox Cloud-Init to Deploy Your Virtual Machines! Kubernetes At Home - Part 2 - YouTube

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