Tutorial: Formatting a notification by using an AWS Lambda function

Create a new AWS Lambda function.

1. In the AWS Lambda console, choose Create function.

2. In Create function, select Use a blueprint.

   Search for and select the hello-world-python blueprint, and then choose Configure.

3. In Basic information:

   1. In Function name, enter the name of this function, format-high-temp-notification.

   2. In Execution role, choose Create a new role from AWS policy templates.

   3. In Role name, enter the name of the new role, format-high-temp-notification-role.

   4. In Policy templates - optional, search for and select Amazon SNS publish policy.

   5. Choose Create function.

Modify the blueprint code to format and send an Amazon SNS notification.

1. After you created your function, you should see the format-high-temp-notification details page. If you don't, open it from the Lambda Functions page.

2. In the format-high-temp-notification details page, choose the Configuration tab and scroll to the Function code panel.

3. In the Function code window, in the Environment pane, choose the Python file, lambda_function.py.

4. In the Function code window, delete all of the original program code from the blueprint and replace it with this code.

   import boto3
   #
   #   expects event parameter to contain:
   #   {
   #       "device_id": "32",
   #       "reported_temperature": 38,
   #       "max_temperature": 30,
   #       "notify_topic_arn": "arn:aws:sns:us-east-1:57EXAMPLE833:high_temp_notice"
   #   }
   # 
   #   sends a plain text string to be used in a text message
   #
   #      "Device {0} reports a temperature of {1}, which exceeds the limit of {2}."
   #   
   #   where:
   #       {0} is the device_id value
   #       {1} is the reported_temperature value
   #       {2} is the max_temperature value
   #
   def lambda_handler(event, context):
   
       # Create an SNS client to send notification
       sns = boto3.client('sns')
   
       # Format text message from data
       message_text = "Device {0} reports a temperature of {1}, which exceeds the limit of {2}.".format(
               str(event['device_id']),
               str(event['reported_temperature']),
               str(event['max_temperature'])
           )
   
       # Publish the formatted message
       response = sns.publish(
               TopicArn = event['notify_topic_arn'],
               Message = message_text
           )
   
       return response

5. Choose Deploy.

In a new window, look up the Amazon Resource Name (ARN) of your Amazon SNS topic from the tutorial about how to Tutorial: Sending an Amazon SNS notification.

1. In a new window, open the Topics page of the Amazon SNS console.

2. In the Topics page, find the high_temp_notice notification topic in the list of Amazon SNS topics.

3. Find the ARN of the high_temp_notice notification topic to use in the next step.

Create a test case for your Lambda function.

1. In the Lambda Functions page of the console, on the format-high-temp-notification details page, choose Select a test event in the upper right corner of the page (even though it looks disabled), and then choose Configure test events.

2. In Configure test event, choose Create new test event.

3. In Event name, enter SampleRuleOutput.

4. In the JSON editor below Event name, paste this sample JSON document. This is an example of what your AWS IoT rule will send to the Lambda function.

   {
     "device_id": "32",
     "reported_temperature": 38,
     "max_temperature": 30,
     "notify_topic_arn": "arn:aws:sns:us-east-1:57EXAMPLE833:high_temp_notice"
   }

5. Refer to the window that has the ARN of the high_temp_notice notification topic and copy the ARN value.

6. Replace the notify_topic_arn value in the JSON editor with the ARN from your notification topic.

   Keep this window open so you can use this ARN value again when you create the AWS IoT rule.

7. Choose Create.

Test the function with sample data.

1. In the format-high-temp-notification details page, in the upper-right corner of the page, confirm that SampleRuleOutput appears next to the Test button. If it doesn't, choose it from the list of available test events.

2. To send the sample rule output message to your function, choose Test.

Open the Rules hub of the AWS IoT console.

To start creating your new rule in Rules, choose Create.

In the top part of Create a rule:

1. In Name, enter the rule's name, wx_friendly_text.

   Remember that a rule name must be unique within your AWS account and Region, and it can't have any spaces. We've used an underscore character in this name to separate the two words in the rule's name.

2. In Description, describe the rule.

   A meaningful description makes it easier to remember what this rule does and why you created it. The description can be as long as needed, so be as detailed as possible.

In Rule query statement of Create a rule:

1. In Using SQL version, select 2016-03-23.

2. In the Rule query statement edit box, enter the statement:

   SELECT 
     cast(topic(2) AS DECIMAL) as device_id, 
     temperature as reported_temperature,
     30 as max_temperature,
     'arn:aws:sns:us-east-1:57EXAMPLE833:high_temp_notice' as notify_topic_arn
   FROM 'device/+/data' WHERE temperature > 30

   This statement:

   • Listens for MQTT messages with a topic that matches the device/+/data topic filter and that have a temperature value greater than 30.

   • Selects the second element from the topic string, converts it to a decimal number, and then assigns it to the device_id field.

   • Selects the value of the temperature field from the message payload and assigns it to the reported_temperature field.

   • Creates a constant value, 30, to represent the limit value and assigns it to the max_temperature field.

   • Creates a constant value for the notify_topic_arn field.

3. Refer to the window that has the ARN of the high_temp_notice notification topic and copy the ARN value.

4. Replace the ARN value (arn:aws:sns:us-east-1:57EXAMPLE833:high_temp_notice) in the rule query statement editor with the ARN of your notification topic.

In Set one or more actions:

1. To open up the list of rule actions for this rule, choose Add action.

2. In Select an action, choose Send a message to a Lambda function.

3. To open the selected action's configuration page, at the bottom of the action list, choose Configure action.

In Configure action:

1. In Function name, choose Select.

2. Choose format-high-temp-notification.

3. At the bottom of Configure action, choose Add action.

4. To create the rule, at the bottom of Create a rule, choose Create rule.

In the MQTT client in the AWS IoT console, subscribe to the input topics, in this case, device/+/data.

1. In the MQTT client, under Subscriptions, choose Subscribe to a topic.

2. In Subscription topic, enter the topic of the input topic filter, device/+/data.

3. Keep the rest of the fields at their default settings.

4. Choose Subscribe to topic.

   In the Subscriptions column, under Publish to a topic, device/+/data appears.

Publish a message to the input topic with a specific device ID, device/32/data. You can't publish to MQTT topics that contain wildcard characters.

1. In the MQTT client, under Subscriptions, choose Publish to topic.

2. In the Publish field, enter the input topic name, device/32/data.

3. Copy the sample data shown here and, in the edit box below the topic name, paste the sample data.

   {
     "temperature": 38,
     "humidity": 80,
     "barometer": 1013,
     "wind": {
       "velocity": 22,
       "bearing": 255
     }
   }

4. To publish your MQTT message, choose Publish to topic.

Confirm that the text message was sent.

1. In the MQTT client, under Subscriptions, there is a green dot next to the topic to which you subscribed earlier.

   The green dot indicates that one or more new messages have been received since the last time you looked at them.

2. Under Subscriptions, choose device/+/data to check that the message payload matches what you just published and looks like this:

   {
     "temperature": 38,
     "humidity": 80,
     "barometer": 1013,
     "wind": {
       "velocity": 22,
       "bearing": 255
     }
   }

3. Check the phone that you used to subscribe to the SNS topic and confirm the contents of the message payload look like this:

   Device 32 reports a temperature of 38, which exceeds the limit of 30.

   If you change the topic ID element in the message topic, remember that casting the topic(2) value to a numeric value will only work if that element in the message topic contains only numeric characters.

Try sending an MQTT message in which the temperature does not exceed the limit.

1. In the MQTT client, under Subscriptions, choose Publish to topic.

2. In the Publish field, enter the input topic name, device/33/data.

3. Copy the sample data shown here and, in the edit box below the topic name, paste the sample data.

   {
     "temperature": 28,
     "humidity": 80,
     "barometer": 1013,
     "wind": {
       "velocity": 22,
       "bearing": 255
     }
   }

4. To send your MQTT message, choose Publish to topic.

You should see the message that you sent in the device/+/data subscription; however, because the temperature value is below the max temperature in the rule query statement, you shouldn't receive a text message.

If you don't see the correct behavior, check the troubleshooting tips.