This page explains how to build a deployable Ubuntu image with packer.
Install packer
Packer is easily installed from its Debian package:
sudo apt install packer
This should install with no additional prompts.
Install dependencies
sudo apt install qemu-utils
sudo apt install qemu-system
sudo apt install ovmf
sudo apt install cloud-image-utils
All of these should install with no additional prompts.
Get templates
You can obtain the packer templates by cloning the packer-maas github repository^, like this:
git clone https://github.com/canonical/packer-maas.git
Make sure to pay attention to where the repository is cloned. The Packer template in this cloned repository creates a Ubuntu AMD64 image for use with MAAS.
Create the image
Build a raw image
To build a packer image, you must change to the template repository directory, then to the subdirectory for the image you want to build. From that subdirectory, you can easily build a raw image with LVM, using the Makefile:
$ make custom-ubuntu-lvm.dd.gz
This makefile will run for a couple of minutes before attempting to boot the image. While waiting for the image to boot, packer will attempt to SSH into the machine repeatedly until it succeeds. You will see terminal messages similar to this one for upwards of three to five minutes:
2022/05/09 15:50:46 packer-builder-qemu plugin: [DEBUG] handshaking with SSH
2022/05/09 15:50:50 packer-builder-qemu plugin: [DEBUG] SSH handshake err: ssh: handshake failed: ssh: unable to authenticate, attempted methods [none password], no supported methods remain
2022/05/09 15:50:50 packer-builder-qemu plugin: [DEBUG] Detected authentication error. Increasing handshake attempts.
Eventually, you should see a successful SSH connection:
2022/05/09 15:50:57 packer-builder-qemu plugin: [INFO] Attempting SSH connection to 127.0.0.1:2351...
2022/05/09 15:50:57 packer-builder-qemu plugin: [DEBUG] reconnecting to TCP connection for SSH
2022/05/09 15:50:57 packer-builder-qemu plugin: [DEBUG] handshaking with SSH
2022/05/09 15:51:17 packer-builder-qemu plugin: [DEBUG] handshake complete!
If the process seems to run for a long time, you can predict whether it’s going to work by doing a series of netstat -a on the IP:port given in the connection attempt. Attempts may fail repeatedly, but if you repeat the netstat -a command frequently, you will see some tentative connections, like this one:
stormrider@neuromancer:~$ netstat -a | grep 2281
tcp 0 0 0.0.0.0:2281 0.0.0.0:* LISTEN
tcp 0 0 localhost:46142 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46120 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46138 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46134 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46130 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46124 localhost:2281 TIME_WAIT
stormrider@neuromancer:~$ netstat -a | grep 2281
tcp 0 0 0.0.0.0:2281 0.0.0.0:* LISTEN
tcp 0 0 localhost:46142 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46146 localhost:2281 ESTABLISHED
tcp 0 0 localhost:2281 localhost:46146 ESTABLISHED
tcp 0 0 localhost:46138 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46134 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46130 localhost:2281 TIME_WAIT
tcp 0 0 localhost:46124 localhost:2281 TIME_WAIT
This ESTABLISHED connection may not hold the first few times, but eventually, the SSH connection will be made, and the provisioning process will finish. If you want to walk away and come back, be advised that the Makefile clears the terminal buffer at the end, but echoes one final instruction:
rm OVMF_VARS.fd
Validate the build
You can check the validity of the operation with ls, like this:
stormrider@neuromancer:~/mnt/Dropbox/src/git/packer-maas/ubuntu$ ls
custom-ubuntu-lvm.dd.gz packages seeds-lvm.iso user-data-lvm
http packer_cache ubuntu-flat.json
Makefile README.md ubuntu-lvm.json
meta-data scripts user-data-flat
OR run manually
You can also manually run packer. Your current working directory must be in the subdirectory where the packer template is located. In the case of this example, that’s packer-maas/ubuntu. Once in packer-maas/ubuntu, you can generate an image with the following command sequence:
$ sudo PACKER_LOG=1 packer build ubuntu-lvm.json
ubuntu-lvm.json is configured to run Packer in headless mode. Only Packer output will be seen. If you wish to see the installation output connect to the VNC port given in the Packer output, or change the value of headless to false in the JSON file.
This process is non-interactive.
Upload to MAAS
You can upload an Ubuntu raw packer image with the following command:
$ maas admin boot-resources create \
name='custom/ubuntu-raw' \
title='Ubuntu Custom RAW' \
architecture='amd64/generic' \
filetype='ddgz' \
content@=custom-ubuntu-lvm.dd.gz
Verify the image
Before relying on it in production, you should test your custom image by deploying it to a test (virtual) machine. It’s the machine named open-gannet in this listing:
maas admin machines read | jq -r '(["HOSTNAME","SYSID","POWER","STATUS",
"OWNER", "OS", "DISTRO"] | (., map(length*"-"))),
(.[] | [.hostname, .system_id, .power_state, .status_name, .owner // "-",
.osystem, .distro_series]) | @tsv' | column -t
HOSTNAME SYSID POWER STATUS OWNER OS DISTRO
-------- ----- ----- ------ ----- -- ------
valued-moth e86c7h on Deployed admin ubuntu focal
open-gannet nk7x8y on Deployed admin custom ubuntu-raw
Log in to verify
You should log into your newly-deployed image and verify that it has all the customisations you added to the build process. The default username for packer-created images is ubuntu, the same as the default username for other MAAS images.