Machine-specific data, such as SSH keys, should not be included in the
immutable root filesystem image, as this would prevent multiple machines
running from the same image. These few files can be stored locally, on
the SD card on eMMC flash.
The first time a machine boots up using this image, its local storage is
initialized. This involves creating a new filesystem on the block
device and generating SSH host keys. Once the storage is initialized,
it is remounted read-only. All subsequent mounts are read-only as well.
Using zram to compress pages did not provide enough memory to run
Firefox, Node, and Python for an extended period of time. Here's hoping
swap-on-NBD will be fast and reliable enough to work.
Note that systemd's default behavior with respect to swap areas is to
enable them all rather early in the boot process, before the network is
fully configured. As such, we have to use the *noauto* flag to disable
the default dependencies and add our own in a later target.
[Playwright] is a cross-browser automation framework, intended for
automating browser-based GUI application tests. It also works as a
general remote-control tool for automating basically anything having to
do with a browser.
Playwright requires a special Firefox binary that it manages itself. To
avoid downloading and installing Playwright and Firefox, and thus
storing them in memory, we need them to be already available in the
rootfs image. Since I want the control software to be updated easily,
without rebooting the machine, I decided to separate it into its own
project, [Voonex]. A short shell script to install/update and run it is
launched by the systemd user instance.
[Playwright]: https://playwright.dev/
[Voonex]: https://git.pyrocufflink.blue/dustin/voonex
Matchbox Window Manager, being designed for mobile devices, does not
handle multiple monitors well. It manages the monitors together as one
giant screen, which will make it extremely difficult to manage separate
Firefox windows on each screen. Openbox is almost as lightweight as
Matchbox, but it works significantly better for this use case.
Dustin