Create a detector model to represent device states in AWS IoT Events

In Create an AWS IoT Events input to capture device data, you created an input based on a message that reports pressure data from a motor. To continue with the example, here is a detector model that responds to an over-pressure event in a motor.

You create two states: "Normal", and "Dangerous". Each detector (instance) enters the "Normal" state when it's created. The instance is created when an input with a unique value for the key "motorid" arrives.

If the detector instance receives a pressure reading of 70 or greater, it enters the "Dangerous" state and sends an Amazon SNS message as a warning. If the pressure readings return to normal (less than 70) for three consecutive inputs, the detector returns to the "Normal" state and sends another Amazon SNS message as an all clear.

This example detector model assumes you have created two Amazon SNS topics whose Amazon Resource Names (ARNs) are shown in the definition as "targetArn": "arn:aws:sns:us-east-1:123456789012:underPressureAction" and "targetArn": "arn:aws:sns:us-east-1:123456789012:pressureClearedAction".

For more information, see the Amazon Simple Notification Service Developer Guide and, more specifically, the documentation of the CreateTopic operation in the Amazon Simple Notification Service API Reference.

This example also assumes you have created an AWS Identity and Access Management (IAM) role with appropriate permissions. The ARN of this role is shown in the detector model definition as "roleArn": "arn:aws:iam::123456789012:role/IoTEventsRole". Follow the steps in Setting up permissions for AWS IoT Events to create this role and copy the ARN of the role in the appropriate place in the detector model definition.

You can create the detector model using the following AWS CLI command.

aws iotevents create-detector-model  --cli-input-json file://motorDetectorModel.json

The file "motorDetectorModel.json" contains the following.

{
  "detectorModelName": "motorDetectorModel",
  "detectorModelDefinition": {
    "states": [
      {
        "stateName": "Normal",
        "onEnter": {
          "events": [
            {
              "eventName": "init",
              "condition": "true",
              "actions": [
                {
                  "setVariable": {
                    "variableName": "pressureThresholdBreached",
                    "value": "0"
                  }
                }
              ]
            }
          ]
        },
        "onInput": {
          "transitionEvents": [
            {
              "eventName": "Overpressurized",
              "condition": "$input.PressureInput.sensorData.pressure > 70",
              "actions": [
                {
                  "setVariable": {
                    "variableName": "pressureThresholdBreached",
                    "value": "$variable.pressureThresholdBreached + 3"
                  }
                }
              ],
              "nextState": "Dangerous"
            }
          ]
        }
      }, 
      {
        "stateName": "Dangerous",
        "onEnter": {
          "events": [
            {
              "eventName": "Pressure Threshold Breached",
              "condition": "$variable.pressureThresholdBreached > 1",
              "actions": [
                {
                  "sns": {
                    "targetArn": "arn:aws:sns:us-east-1:123456789012:underPressureAction"
                  }
                }
              ]
            }
          ]
        },
        "onInput": {
          "events": [
            {
              "eventName": "Overpressurized",
              "condition": "$input.PressureInput.sensorData.pressure > 70",
              "actions": [
                {
                  "setVariable": {
                    "variableName": "pressureThresholdBreached",
                    "value": "3"
                  }
                }
              ]
            },
            {
              "eventName": "Pressure Okay",
              "condition": "$input.PressureInput.sensorData.pressure <= 70",
              "actions": [
                {
                  "setVariable": {
                    "variableName": "pressureThresholdBreached",
                    "value": "$variable.pressureThresholdBreached - 1"
                  }
                }
              ]
            }
          ],
          "transitionEvents": [
            {
              "eventName": "BackToNormal",
              "condition": "$input.PressureInput.sensorData.pressure <= 70 && $variable.pressureThresholdBreached <= 1",
              "nextState": "Normal"
            }
          ]
        },
        "onExit": {
          "events": [
            {
              "eventName": "Normal Pressure Restored",
              "condition": "true",
              "actions": [
                {
                  "sns": {
                    "targetArn": "arn:aws:sns:us-east-1:123456789012:pressureClearedAction"
                  }
                }
              ]
            }
          ]
        }
      }
    ],
    "initialStateName": "Normal"
  },
  "key" : "motorid",
  "roleArn": "arn:aws:iam::123456789012:role/IoTEventsRole"
}