Running Voonex (Python), Playwight (Node.js), and Firefox simultaneously
takes way too much memory. Using the NBD swap prevents hard lockups and
crashes in OOM situations, but it makes the machine *incredibly* slow.
To avoid needing to push anything into the network swap, I want to try
and reduce the memory footprint as much as possible. To that end, we
will go back to running just Firefox. To control it, we will use the
Marionette protocol.
Firefox only allows control via Marionette over the loopback interface.
This is hard-coded in the Marionette server, and cannot be changed at
runtime. To allow a remote machine (running Voonex) to control it, we
need to expose the socket to the network. Fortunately, *systemd*
includes a tool for exactly this purpose: `systemd-socket-proxyd`.
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.
[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