领航计划（四）理解 KubeEdge Device twin

• 【本文正在参加2023年第一期优质创作者激励计划】

什么是 Device twin

Device twin

• 设备的动态属性，在 KubeEdge 中的设备孪生 包含了desired value(期望值)和reported value(真实值)，这对于开放你自己边缘应用的使用是更重要的
• 在 KubeEdge 利用 Device Model 和 Device Instance 的机制，通过一套 Device Model 生成大量 Device Instance 的机制实现关联管理，模具和事物的关系

Device Commpents in KubeEdge

Membership Module

• 该模块主要负责绑定新加入的设备与指定的边缘节点（其实就是NodeSelector的体现）

Twin Module

• 该模块主要负责所有设备孪生相关的操作。比如，设备孪生更新（device twin update）、设备孪生获取（device twin get）和设备孪生同步至云端（device twin sync-to-cloud）

Communication Module

• 该模块主要负责各个子模块之间的通信

Device Module

• 该模块主要负责执行设备相关的操作，比如处理设备状态（device status）更新和设备属性（device attribute）更新
• 此外，DeviceTwin模块会在本地数据库（SQLite）中创建3张表，即Device Table、Device Attribute Table和Device Twin Table，分别记录设备的基本信息、设备的属性信息和设备孪生信息。

MoreInfo Device Model

• 如何定义Device Model
  一个 Device Model 的资源文件大概是:

apiVersion: devices.kubeedge.io/v1alpha2
kind: DeviceModel
metadata:
 name: sensor-tag-model
 namespace: default
spec:
 properties:
  - name: temperature
    description: temperature in degree celsius
    type:
     int:
      accessMode: ReadWrite
      maximum: 100
      unit: degree celsius
  - name: temperature-enable
    description: enable data collection of temperature sensor
    type:
      string:
        accessMode: ReadWrite
        defaultValue: 'OFF'

MoreInfo Device Instance

• 如何定义Device Instance

一个 Device Instance 大概是：

apiVersion: devices.kubeedge.io/v1alpha2
kind: Device
metadata:
  name: sensor-tag-instance-01
  labels:
    description: TISimplelinkSensorTag
    manufacturer: TexasInstruments
    model: CC2650
spec:
  deviceModelRef:
    name: sensor-tag-model
  protocol:
    modbus:
      slaveID: 1
    common:
      com:
        serialPort: '1'
        baudRate: 115200
        dataBits: 8
        parity: even
        stopBits: 1
  nodeSelector:
    nodeSelectorTerms:
    - matchExpressions:
      - key: ''
        operator: In
        values:
        - node1
  propertyVisitors:
    - propertyName: temperature
      modbus:
        register: CoilRegister
        offset: 2
        limit: 1
        scale: 1
        isSwap: true
        isRegisterSwap: true
    - propertyName: temperature-enable
      modbus:
        register: DiscreteInputRegister
        offset: 3
        limit: 1
        scale: 1.0
        isSwap: true
        isRegisterSwap: true
status:
  twins:
    - propertyName: temperature
      reported:
        metadata:
          timestamp: '1550049403598'
          type: int
        value: '10'
      desired:
        metadata:
          timestamp: '1550049403598'
          type: int

Data Topic

• 在KubeEdge v1.4之后，也添加了可以在边缘端的Data topic模块

apiVersion: devices.kubeedge.io/v1alpha1
kind: Device
metadata:
    ...
spec:
  deviceModelRef:
    ...
  protocol:
    ...
  nodeSelector:
    ...
  propertyVisitors:
    ...
  data:
    dataTopic: "$ke/events/device/+/data/update"
    dataProperties:
      - propertyName: pressure
        metadata:
          type: int
      - propertyName: temperature
        metadata:
          type: int

Topic 汇总