Replace Ubuntu Server with Alpine Linux

[jiayihu]

Current OS is Ubuntu Server 20.04 as done in #18 but Alpine Linux is much smaller, although requires much more initial configuration. Alpine Linux requires only about 130MB storage, 8MB RAM.

Alpine Linux for Raspberry Pi aarch64 is available at https://alpinelinux.org/downloads/

• K3s bootstrap on Alpine Linux
• Installing Alpine Linux on a Raspberry Pi
• Installing in a Alpine VM error https://github.com/k3s-io/k3s/issues/1387
• Alpine Linux Init System

[jiayihu]

Steps:

• Enable root ssh
• Add /etc/init.d to lbu: https://wiki.alpinelinux.org/wiki/Alpine_local_backup
• Configure wpa_supplicant for wifi: https://gitlab.alpinelinux.org/alpine/aports/-/issues/8025
• Add sudo user: https://docs.alpinelinux.org/user-handbook/0.1a/Working/post-install.html
  • https://askubuntu.com/questions/147241/execute-sudo-without-password
• Copy ssh key and disable password login

[jiayihu]

I gave a shot at persistent storage as described in https://wiki.alpinelinux.org/wiki/Raspberry_Pi_4_-_Persistent_system_acting_as_a_NAS_and_Time_Machine but I had an issue where wlan0 device could not be found after reboot. Sticking with immutable storage is fine for the time being, I can revert to previous configs and be sure that a reboot resets to the last working config

[jiayihu]

It also seems that it's not possible to create an user. The changes are not committed and even so they are recreated as root after reboot. https://gitlab.alpinelinux.org/alpine/aports/-/issues/10124

[jiayihu]

K3s server doesn't seem to be working on Alpine Linux due to missing storage. I cannot add cgroup config to extlinux, which is not available in diskless. So I must find a way to mount persistent storage, maybe as described here: https://wiki.alpinelinux.org/wiki/Raspberry_Pi#Persistent_storage

Anyway memory cgroups seems not work neither: https://gitlab.alpinelinux.org/alpine/aports/-/issues/11308

[jiayihu]

Final status: all nodes have been migrated to Alpine Linux. The final status is a diskless mode with persistent overlay in /usr, /var/lib/rancher and /root up to 1GB. Maybe I should have used 2-3GB (4GB is the upper bound of FAT32), but 1GB should be enough. The important files are backed up and immutable, at worst data in overlay can be deleted and the cluster reset (including tokens and certs).

The memory usage of Alpine w/o k3s is 55MB, compared to about ~400MB for Ubuntu Server. With k3s-server it's up to ~500MB in the master, because Go is garbage collected and it prefers to increase the memory if available instead of running the collector. Worker nodes with k3s agent use ~128MB.

[jiayihu]

Opened PR in k3s-ansible adding support for Alpine Linux k3s-io/k3s-ansible#107