Proxmox Cloud-Init OS template creation

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October 4, 2019 | What The Server

Introduction

In this guide we will go over creating a Proxmox KVM Template from a Cloud Image. This same process will work for any Cloud-Init Openstack based image type you can find online.

Having done a number of these for our Proxmox based VPS service I wanted to post up a guide to help anyone else looking to do the same thing.

My workflow for customizing one of those for use with Proxmox with cloud-init deployment from WHMCS and root login is below. Once you setup one template you can rapidly reinstall new containers and test stuff.

Setup Environment

If not installed already installed you will need libguestfs-tools :

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To edit the image before importing. We will use virt-edit which is a part of libguestfs-tools.

For the sake of sanity, I highly advise setting your default editor to “nano” because using the default libguestfs-tools editor is a really frustrating experience to learn and will save a lot of wasted time and errors.

You can see your default editor with the the below command.

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To set nano as default if it’s not already. use the below command. Please Note: nano should be installed(should be by default on Ubuntu/Debian systems)

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It should now look like the below.

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Grab the Cloud Image

Grab the cloud image base link for desired OS: Openstack has a nice page on this: https://docs.openstack.org/image-guide/obtain-images.html

These are some direct links:
https://cloud.centos.org/centos/7/images/
https://cloud-images.ubuntu.com/
https://repo.almalinux.org/almalinux/8/cloud/x86_64/images/

Ssh into your Proxmox server and fetch the image directly to the server. This saves you having to upload it to the server later. Im grabbing latest Centos 7 for this guide.

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Customize Image

We can now use virt-edit to edit the image to enable our desired defaults. The modifications below allows root and password-based logins. Not being able to login to the VPS in novnc without a password is a real pain when trying to fix a network-related issue with the template and it’s locked to key-based.

Here is the format for the command to edit by hand.

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So for our example of “CentOS-7-x86_64-GenericCloud-1907.qcow2” to open up the “/etc/cloud/cloud.cfg” so we can modify it to enable root and password logins. The below command will be used. Note it may take a second to open so be patient.

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Once opened it will look something like this.

The first thing you want to do is carefully edit the disable_root: 1 to disable_root: 0 This will set cloud-init to not disable this in the /etc/ssh/sshd_config on first boot and allow root based logins. It should look like the below.

Please note some OS cloud images use “true” or “false” where 1=true and 0=false. If they are using true and false vs 1 and 0 please use that formatting.

Next we need to toggle the “lock_passwd” from “true” to “false” Without this you will be unable to use password-based authentication for the account. Scroll down towards the bottom of the file and look for the default user section. See below.

Once fixed it will look like this.

Another way to do the above is automatically via sed like manner non-interactively as outlined in the below link.

https://libguestfs.org/virt-edit.1.html#non-interactive-editing

To enable root and password logins for example the below commands could be used which accounts for all variations of True/true/1 being set which has it disabled.

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Next part is optional and would go in this same file. I find it handy to splice in the qemu-guest-agent and other stuff I want to be installed right out of the box for the template. The formatting is crucial so make sure you copy it and maintain the yaml formatting that cloud-init config file is based on.

packages:
 - qemu-guest-agent
 - nano
 - wget
 - curl
 - net-tools

Should look like this. Sometimes I have to put these packages above the ssh_svcname: sshd block for some OS. So if it doesn’t work insert it above that block. See the cloud-init documentation for more details.

Now you can use ctrl+x and hit y to save and exit.

You can also splice in packages which is faster directly into the image which saves on the install first boot time by using virt-customize to inject/install packages into the image like in the below command.

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Modify the sshd_config

Now we need to ensure the default /etc/ssh/sshd_config is setup to our liking and allows root login. We need to ensure the below values are set.

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So now we reopen the image but this time were editing the file “/etc/ssh/sshd_config”

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Now we need to look for “PermitRootLogin” it may be commented out or set to “PermitRootLogin no” or “PermitRootLogin without-password”. make sure only one occurrence is enabled and it says “PermitRootLogin yes” like the below example.

To enable root logins via ssh and password authentication the below command will also handle that for you.

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Now we will scroll down and verify that “PasswordAuthentication yes” is set. Sometimes it is sometimes it isn’t so always check. In this template it was enabled. So we can save and close this now if no other customization’s are needed.

Editing existing images of imported images

Occasionally you will find you got everything except one thing working and you want to modify the image of existing VM. This is totally possible just ensure that the guest VM is completely powered off first.

To edit an already imported disk. This example is based on the vm with id 104. You may need to verify the full path to the disk as the disk image name may vary depending on your environment.

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Creating VM

Here we are going to tie it all together.

Create the VM: See the official link > https://pve.proxmox.com/wiki/Cloud-Init_Support

You may need to create the container if it does not exist already. The below is based on my storage for OS template VM using “local” storage yours may be “zfs” or “local-lvm” etc so may need to update those paths to suit your environment.

Create a new VM

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Import the downloaded disk to local storage

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Finally attach the new disk to the VM as scsi drive

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Add Cloud-Init CDROM drive

The next step is to configure a CDROM drive which will be used to pass the Cloud-Init data to the VM.

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To be able to boot directly from the Cloud-Init image, set the bootdisk parameter to scsi0, and restrict BIOS to boot from disk only. This will speed up booting, because VM BIOS skips the testing for a bootable CDROM.

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Also configure a serial console and use it as a display. Many Cloud-Init images rely on this, as it is an requirement for OpenStack images.

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In a last step, it is helpful to convert the VM into a template. From this template you can then quickly create linked clones. The deployment from VM templates is much faster than creating a full clone (copy).

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Create a clone from the previous template.

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Batch mode:

If you want to do this for a lot it can be tedious but you can do it pretty quickly with the below as a reference. The only thing to really change would be the cloud_image_url and vm_id variable and the rest should just go like clockwork.

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Create a text file named images.txt

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Then you can run the below. I have done a loop through a bunch of urls like the below to prep them all in batch mode.

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Conclusion

I hope you found this tutorial helpful in creating a Proxmox cloud-init KVM template. There is so much more you can do with cloud-init and libguestfs-tools like injecting apps and repos in the image before its even booted. We recommend making backups before major edits so you can revert back to the base image if there is an issue.

Resource and reference links.

https://docs.openstack.org/image-guide/modify-images.html

http://libguestfs.org/virt-edit.1.html

https://www.poftut.com/linux-kvm-qemu-virt-customize-tutorial/

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