Zigbee2MQTT commits the cardinal sin of storing state in its
configuration file. This means the file has to be writable and thus
stored in persistent storage rather than in a ConfigMap. As a
consequence, making changes to the configuration when the application is
not running is rather difficult. Case in point: when I added the
internal alias for _mqtt.pyrocufflink.blue_ pointing to the in-cluster
service, Zigbee2MQTT became unable to connect to the broker because it
was using the node port instead of the internal port. Since it could
not connect to the broker, it refused to start, and thus the container
would not stay running long enough to fix the configuration to point
to the correct port.
Fortunately, Zigbee2MQTT also allows configuring settings via
environment variables, which can be managed with a ConfigMap. Luckily,
the values read from environment variables override those from the
configuration file, so pointing to the correct broker port with the
environment variable was sufficient to allow the application to start.
Dustin