How to Republish MQTT Messages Using AWS IoT Rules
AWS IoT provides a feature called AWS IoT Rules.
AWS IoT rules send data from your devices to other AWS services. They listen for specific MQTT messages, format the data in the message payloads, and send the result to other AWS services.
Creating AWS IoT rules to route device data to other services
By using AWS IoT Rules, you can send data within messages to various AWS resources.
In this article, we will explore how to republish received MQTT messages. We will create AWS IoT Rules and an IAM role to republish messages from one topic to another. As a result, you can efficiently extract and process message content and redistribute it to different topics.
Refer to the following page to see how to re-issue received MQTT messages.
Configuration
- Create an AWS IoT Rule that republishes messages published to a topic to another topic.
- Create an IAM role for the AWS IoT Rule.
Resources
AWS IoT Rule
The rule is structured like an SQL statement. For details, please refer to the following page:
Data
In this rule, we create a message composed of two data elements: device_id and temperature.
- temperature: Use the data of the same name contained in the message that was the subject of the rule.
- device_id: Use the second string from the topic name split with slashes using the topic function.
Returns the topic to which the message that triggered the rule was sent. If no parameter is specified, the entire topic is returned.
topic(Decimal)
FROM Clause
In the FROM clause, we specify the topic name from which to retrieve data. We target the topic device/+/data.
SQL Version
You can set the SQL version. The “2016-03-23” version we specify is explained by AWS as follows:
2016-03-23 – The SQL version built on 2016-03-23 (recommended).
SQL versions
Republish Action
You can set the level of Quality of Service (QoS) with the Qos property. The levels can be “0” or “1”; we specify “0” this time. AWS explains this level as follows:
Sent zero or more times
This level should be used for messages that are sent over reliable communication links or that can be missed without a problem.
MQTT Quality of Service (QoS) options
We specify device/data/temp as the destination topic for republishing.
IAM Role
In the trust policy, we allow the iot.amazonaws.com service to assume this IAM role. The IAM policy attached to the role permits the iot:Publish action. We specify the ARN of the destination topic for republishing, allowing messages to be sent to this topic.
CloudFormation Template
AWS IoT Rule
Resources:
TopicRule:
Type: AWS::IoT::TopicRule
Properties:
RuleName: republish_temp
TopicRulePayload:
Actions:
-
Republish:
Qos: 0
RoleArn: !GetAtt TopicRuleRole.Arn
Topic: !Ref DestTopicName
AwsIotSqlVersion: 2016-03-23
RuleDisabled: false
Sql: !Sub "SELECT topic(2) as device_id, temperature FROM '${SourceTopicName}'"
Code language: YAML (yaml)IAM Role
Resources:
TopicRuleRole:
Type: AWS::IAM::Role
DeletionPolicy: Delete
Properties:
AssumeRolePolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Action: sts:AssumeRole
Principal:
Service:
- iot.amazonaws.com
Policies:
- PolicyName: TopicRulePolicy
PolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Action:
- iot:Publish
Resource:
- !Sub "arn:aws:iot:${AWS::Region}:${AWS::AccountId}:topic/${DestTopicName}"
Code language: YAML (yaml)Full Template
Verification
Now that everything is set up, we will verify the operation by accessing the MQTT test client page.
First, subscribe to two topics:
- device/+/data
- device/data/temp
Next, publish a message to the topic device/22/data.
We can receive the message on device/+/data. This topic uses wildcard notation and can receive the message we just published.
Now, check device/data/temp.
A message has also arrived here. AWS IoT Rules republished the message to this topic.
Looking at the content of the message, it includes two data elements: device_id and temperature. The former is part of the topic name, and the latter is data included in the original message before republishing.
Conclusion
By using AWS IoT Rules, you can republish messages. By properly configuring the SQL expression, which is the essence of the rule, you can extract and process the content of the messages to be republished. This enables efficient management and utilization of IoT data.