feat: create environment variable for the config file

[wilmardo]

Introduces an environment variable for the configuration.yaml location.

Since the devices and groups can be split off this can be used to build the configuration into a Docker image since it doesn't require writing to.

For example:

# Home Assistant integration (MQTT discovery)
homeassistant: false

# allow new devices to join
permit_join: true

# MQTT settings
mqtt:
  # MQTT base topic for zigbee2mqtt MQTT messages
  base_topic: zigbee2mqtt
  # MQTT server URL
  server: "mqtt://localhost"
  # MQTT server authentication, uncomment if required:
  # user: my_user
  # password: my_password

# Serial settings
serial:
  # Location of CC2531 USB sniffer
  port: /dev/ttyACM0

# Map devices to persistent /data directory
devices: /data/devices.yaml
groups: /data/groups.yaml

advanced:
  log_output: ["console"]

This still persists the devices and groups to a volume but the configuration can be built into the image since it doesn't require changing.

I need this for to be able to use a Kubernetes configmap for the configuration. Kubernetes makes the folder where the configmap is mounted to read-only. In the current scenario this means that the whole /data directory becomes read-only. Zigbee2Mqtt tries to write the state.json to there so that results in an error.
This env var allows the configuration to exists in /config and keep the /data directory writable.

[wilmardo]

BTW, when you are open to merging this I will add some documentation :)

[Koenkk]

Currently it is already possible to set a different location for the data directory (which contains configuration.yaml) ZIGBEE2MQTT_DATA, does this have any added value?

[wilmardo]

Yes it does, I will try to elaborate it a bit more.

This is an example deployment for the container on Kubernetes (simplified, full example here)

---
apiVersion: apps/v1
kind: Statefulset
metadata:
  name: zigbee2mqtt
spec:
  template:
    spec:
      containers:
        - name: zigbee2mqtt
          image: lansible/zigbee2mqtt:master
          env:
            - name: ZIGBEE2MQTT_DATA
              value: /data
          volumeMounts:
            - name: zigbee2mqtt-data
              mountPath: /data
            - name: zigbee-usb
              mountPath: /dev/ttyACM0
      volumes:
        - name: zigbee2mqtt-config
          configMap:
            name: zigbee2mqtt-config
        - name: zigbee2mqtt-data
          hostPath:
            path: /data/zigbee2mqtt-zigbee2mqtt-data
        - name: zigbee-usb
          hostPath:
            path: /dev/serial/by-id/usb-Texas_Instruments_TI_CC2531_USB_CDC___0X00124B00194AD7EC-if00
            type: CharDevice

This works as expected, the only thing is, I need to login to the node to edit the configuration.yaml. Kubernetes has a nice resource dedicated to this named configmap (docs) which can be deployed with the app.

Example:

---
apiVersion: v1
kind: ConfigMap
metadata:
  name: zigbee2mqtt-config
data:
  configuration.yaml: |
    # Home Assistant integration (MQTT discovery)
    homeassistant: true

    # allow new devices to join
    permit_join: true

    # MQTT settings
    mqtt:
      # MQTT base topic for zigbee2mqtt MQTT messages
      base_topic: zigbee2mqtt
      # MQTT server URL
      server: 'mqtt://mosquitto:1883'
      user: zigbee2mqtt
      password: password

    # Serial settings
    serial:
      # Location of CC2531 USB sniffer
      port: /dev/ttyACM0

    # Map devices to persistant storage
    devices: /data/devices.yaml
    groups: /data/groups.yaml

    advanced:
      log_output: ["console"]
      log_level: debug

The problem here is that the folder where the configmap gets mounted will become readonly by design (issue).
So the current setup with /data/configuration.yaml does not work because /data will become readonly. Zigbee2Mqtt tries to write its state.json/devices.yaml/groups.yaml but errors since /data has become readonly.
This variable makes it possible to keep /data writable by mounting the config somewhere else (/config for example).

The patched deployment with /config readonly and the configmap mounted and /data still writeable:

---
apiVersion: apps/v1
kind: Statefulset
metadata:
  name: zigbee2mqtt
spec:
  template:
    spec:
      containers:
        - name: zigbee2mqtt
          image: lansible/zigbee2mqtt:master
          env:
            - name: ZIGBEE2MQTT_DATA
              value: /data
            - name: ZIGBEE2MQTT_CONFIG
              value: /config
          volumeMounts:
            - name: zigbee2mqtt-config
              mountPath: /config
            - name: zigbee2mqtt-data
              mountPath: /data
            - name: zigbee-usb
              mountPath: /dev/ttyACM0
      volumes:
        - name: zigbee2mqtt-config
          configMap:
            name: zigbee2mqtt-config
        - name: zigbee2mqtt-data
          hostPath:
            path: /data/zigbee2mqtt-zigbee2mqtt-data
        - name: zigbee-usb
          hostPath:
            path: /dev/serial/by-id/usb-Texas_Instruments_TI_CC2531_USB_CDC___0X00124B00194AD7EC-if00
            type: CharDevice

[Koenkk]

Definitely a valid case indeed, thanks for your comprehensive explanation!