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Image with Packer

MAAS Custom Images

By default, MAAS only includes an image for Ubuntu. If you want to add an image for another operating system, you need to build it in the appropriate format using the Packer application.

Packer Docs

🎯 Goal

To build a clean debian-custom-cloudimg.tar.gz image for MAAS deployment.

🛠️ Environment & Tools

Host Environment:

  • Windows 11 / WSL2 (Ubuntu)
  • Builder: Packer with QEMU builder

Repository:

Clone Canonical's MAAS Image Builder (based on HCL format):

git clone https://github.com/canonical/packer-maas.git
cd packer-maas

1. Packer Configuration (WSL2/QEMU)

The default configuration required modifications primarily due to the Nested Virtualization environment (QEMU running inside WSL2/Hyper-V).

1.1. KVM Acceleration Fix (Crucial for WSL2)

The main build may fail because QEMU attempts to use KVM acceleration (accel=kvm), which is inaccessible from within WSL2, resulting in a "Permission denied" error.

File Modified: debian-cloudimg.pkr.hcl

Original configuration:

# Original (doesn't work in WSL2)
qemu_machine = { "amd64" = "accel=kvm" }
qemu_cpu = { "amd64" = "host" }

Fixed configuration for WSL2 emulation:

locals {
    qemu_machine = { "amd64" = "q35" }   # Use standard machine without KVM flag
    qemu_cpu = { "amd64" = "max" }       # Use safe CPU setting
}

Explanation:

  • Removed hardcoded KVM flags in the locals block
  • Forces pure software emulation (slower but works in WSL2)
  • Uses q35 machine type (standard x86_64 chipset)
  • Uses max CPU model (safe fallback without host-passthrough)

1.2. Boot Mode Configuration

Switched the boot mode to BIOS (BOOT=bios) to avoid potential conflicts with UEFI/OVMF firmware copying and usage within the QEMU environment.

1.3. Build the Image

Run the build command:

make debian SERIES=trixie BOOT=bios

Build process:

  1. Packer downloads the Debian Trixie ISO
  2. QEMU starts the VM in software emulation mode
  3. Automated installation proceeds via preseed
  4. Image is packaged as debian-custom-cloudimg.tar.gz

Expected output:

==> Builds finished. The artifacts of successful builds are:
--> qemu.debian: debian-custom-cloudimg.tar.gz

2. MAAS Deployment Steps

After a successful build, the image is ready for deployment.

2.1. File Transfer

Copy the image to the MAAS server:

scp debian-custom-cloudimg.tar.gz user@maas_server_ip:/home/user/

2.2. Upload Image to MAAS

SSH to the MAAS server and upload the custom image:

ssh user@maas_server_ip

# Upload the custom image
maas admin boot-resources create \
    name='custom/debian-trixie' \
    title='Debian 13 Trixie Custom' \
    architecture='amd64/generic' \
    filetype='tgz' \
    content@=debian-custom-cloudimg.tar.gz

2.3. Verify Image Upload

Check if the image was uploaded successfully:

maas admin boot-resources read

Look for your custom image in the list:

custom/debian-trixie (amd64/generic)

2.4. Deploy to Nodes

Via MAAS UI:

  1. Navigate to Machines
  2. Select a node in Ready state
  3. Click Deploy
  4. Choose custom/debian-trixie from the OS dropdown
  5. Confirm deployment

Via CLI:

maas admin machine deploy <system_id> \
    distro_series='custom/debian-trixie'

🐛 Troubleshooting

Build Fails with "Permission denied" (KVM)

Symptom:

qemu-system-x86_64: failed to initialize kvm: Permission denied

Solution:

Apply the KVM fix in section 1.1 - force software emulation by removing accel=kvm.

Build is Very Slow

Cause:

Software emulation (no KVM) is significantly slower than hardware acceleration.

Expected time:

  • With KVM: 5-10 minutes
  • Without KVM (WSL2): 30-60 minutes

Solution:

Be patient. Consider building on native Linux with KVM support for faster builds.

OVMF/UEFI Boot Issues

Symptom:

Could not find firmware for UEFI boot

Solution:

Use BOOT=bios flag as shown in section 1.2.

📚 Additional Resources