Build Kubernetes QEMU/KVM Image with Packer

Packer is a tools to automate creation of multiple machine images build by Hashicorp. Its support multiple builders such as AWS EC2, DigitalOcean, LXD, VMWare, QEMU, etc. In this post, I will share how to create a packer template to build kubernetes image for QEMU/KVM on top of Ubuntu minimal cloud image based on my homelab setup.

Prerequisites

  • packer
  • cloud-localds (from cloud-image-utils in ubuntu)
  • QEMU/KVM enabled host

Step by Step

  1. Ensure you have QEMU/KVM enabled host, and also packer installed in your machine. If you use Linux, you could use following commands:

    export PACKER_VERSION=1.5.4
    curl -SL https://releases.hashicorp.com/packer/$(PACKER_VERSION)/packer_$(PACKER_VERSION)_linux_amd64.zip -o packer_$(PACKER_VERSION)_linux_amd64.zip
    unzip packer_$(PACKER_VERSION)_linux_amd64.zip
    sudo mv packer /usr/bin/packer
    
  2. Create packer configuration file named kubernetes.json

    Notes the variables section,

    • image_checksum, can be found from SHA256SUMS or use sha256sum <image_file>
    • image_url, can be local path or http(s) path, in this case we use https path from ubuntu cloud minimal release.
    • cloud_init_image, minimal ubuntu cloud image has cloud-init support and need to configured in order to use it properly. We will create the cloud-init image in next step.
    • ssh_username, by default ubuntu cloud minimal image use ubuntu as default user.
    • ssh_password, this value need to be defined in our cloud-init userdata.
  3. Create cloud-init image with following userdata:

    After that, build cloud-init image with following command:

    # ensure cloud-localds command exist, install cloud-image-utils in ubuntu
    sudo apt-get install cloud-image-utils -y
    cloud-localds cloud-init.img userdata.cfg
    
  4. Create Kubernetes setup script, you could follow from Kubernetes docs or use following script:

    Notes following commands:

    • kubeadm config images pull, this command will pull required docker images for kubernetes to run. This will save your time when you bootstrap a cluster, because the docker images are baked to the VM image.
    • sudo apt-mark hold kubelet kubeadm kubectl, this command will ensure the mentioned packages are not upgraded to prevent break when auto-upgrade triggered.
  5. Everything is set! The next step is validate the config and then build the image:

    # might need sudo if user don't have permission to KVM module
    packer validate kubernetes.json
    packer build kubernetes.json
    

    The following logs is an output part of packer build process:

    ==> qemu: Provisioning with shell script: /tmp/packer-shell168629488
    ==> qemu: Halting the virtual machine...
    ==> qemu: Converting hard drive...
    ==> qemu: Error getting file lock for conversion; retrying...
    Build 'qemu' finished.
    
    ==> Builds finished. The artifacts of successful builds are:
    --> qemu: VM files in directory: build
    
  6. Image are ready to use, please note that the size might be too small. You could resize the image with following command qemu-img resize <IMAGE_FILE> +DESIRED_SIZE. Let say we want kubernetes-1584350145.qcow2 which currently has 8GB size, resized to 100GB, then the command will be:

    qemu-img resize kubernetes-1584350145.qcow2 +92G
    
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