Both *zwavejs2mqtt* and *zigbee2mqtt* have various bugs that can cause
them to crash in the face of errors that should be recoverable.
Specifically, when there are network errors, the processes do not always
handle these well. Especially during first startup, they tend to crash
instead of retry. Thus, we'll move the retry logic into systemd.
The *zwavejs2mqtt* and *zigbee2mqtt* services need to wait until the
system clock is fully synchronized before starting. If the system clock
is wrong, they may fail to validate the MQTT server certificate.
The *time-sync.target* unit is not started until after services that
sync the clock, e.g. using NTP. Notably, the *chrony-wait.service* unit
delays *time-sync.target* until `chrony waitsync` returns.
The first time launching a container after pulling a new image, it can
take several minutes for the container to actually start. Podman has to
set up the overlay filesystems, which is very slow on a Raspberry Pi.
With the default start timeout, systemd may end up killing the process
before the container is completely set up. Thus, we need to increase
the timeout to ensure there is plenty of time for Podman to work.
Processes running in containers only have access to a limited set of
devices, based on their SELinux type label. The USB serial devices
exposed by the Zwave and Zigbee adapters are not labelled correctly by
default to allow them to be used in containers.
Using `chcon` to change the type label of the device before starting the
container seems to work, but seems a bit kludgy. It would probably be
better to use a SELinux file context rule and/or a udev rule to ensure
the label is set correctly when the device node is created.
Home Assistant no longer recommends using the built-in libopenzwave
integration for communicating with Z-Wave devices. Evidently, OpenZWave
is no longer maintained, and community efforts have shifted toward
Z-Wave JS.
Z-Wave JS is architecturally much different than the legacy Z-Wave
integration. Instead of running the network controller inside the Home
Assistant process, a separate daemon communicates with the Z-Wave radio.
Home Assistant integrates with that daemon using a WebSockets API. This
has the advantage of decoupling the network operation from the lifecycle
of the Home Assistant process: restarting Home Assistant (e.g. to load
new configuration changes) does not take the Z-Wave network offline.
ZwaveJS2Mqtt is a distribution of the Z-Wave JS daemon, as well as a
web-based user interface for configuring it. Although its name implies
that it uses MQTT for communication, this feature is actually optional,
and the native WebSockets API can still be used for integration with
Home Assistant.
I decided to follow the same deployment pattern for ZwaveJS2Mqtt as for
Home Assistant itself: run the application from a container image using
Podman. This of course simplifies the installation of the application
significantly, leaving most of that work up to the maintainer of the
container image. Podman provides the container runtime, managing the
privileges, etc. The systemd service unit starts Podman, configuring an
ephemeral container on each run. The container uses the default network
namespace, avoiding the unnecessary overhead of port mapping. It uses
Podman's "rootless" mode, via the `--uidmap` and `--gidmap` arguments,
mapping users inside the container, including root, to unprivileged
users on the host. The Z-Wave radio, which is specified by the
`zwavejs_device` Ansible variable, is passed into the container via the
`--device` argument.
Dustin