MQTT

Lightweight messaging protocol ideal for IoT use cases

Overview

This page provides an overview of how Joule utilises the MQTT protocol to subscribe to events, specifically in IoT use cases.

MQTT is a lightweight, publish-subscribe network protocol used for message queuing services, making it ideal for machine-to-machine communication in IoT.

Joule enables the subscription to events through an MQTT source consumer, which allows for the consumption of events from a specified MQTT topic.

Client library: org.eclipse.paho:org.eclipse.paho.mqttv5.client:1.2.5

Examples & DSL attributes

This example illustrates how to configure an MQTT consumer to subscribe to events from the customers topic.

The consumer connects to the MQTT broker at tcp://127.0.0.1:1883 and consumes events with a Quality of Service (QoS) level of 1.

1. Client settings The consumer is identified by the clientId (jouleCustomerConsumer), with authentication using the username joule and the tenant uk.

2. Event deserialisation The events are consumed as customer objects and then transformed into Joule StreamEvent objects using the CustomerToStreamEventTranslator class.

3. Additional settings The configuration also includes settings for compressed (set to false) and batch (set to f

4. alse), which affect how events are processed and transformed.

DSL

mqttConsumer:
  broker: tcp://127.0.0.1:1883
  topic: customers

  clientId: jouleCustomerConsumer
  username: joule
  password: joule
  tenant: uk
  qos: 1

  deserializer:
    parser: com.fractalworks.streams.transport.mqtt.CustomerToStreamEventTranslator
    compressed: false
    batch: false

Parser

Use the Joule SDK to build a custom parser and deploy the resulting jar file to the userlibs directory. See Joule SDK for further information.

import com.fasterxml.jackson.annotation.JsonRootName;
import com.fractalworks.streams.core.data.streams.StreamEvent;
import com.fractalworks.streams.core.exceptions.TranslationException;
import com.fractalworks.streams.sdk.codec.StreamEventParser;
import com.fractalworks.streams.transport.Customer;

import java.util.Collection;
import java.util.Collections;

@JsonRootName(value = "customer parser")
public class CustomerToStreamEventTranslator implements StreamEventParser {

    public CustomerToStreamEventTranslator() {
        // REQUIRED
    }

    @Override
    public Collection<StreamEvent> translate(Object o) throws TranslationException {
        Collection<StreamEvent> events = null;
        if(o instanceof Customer customer){
            StreamEvent event = new StreamEvent("customer");
            event.addValue("id", customer.getId());
            event.addValue("firstname", customer.getFirstname());
            event.addValue("surname", customer.getSurname());
            event.addValue("age", customer.getAge());

            events = Collections.singletonList( event);
        }
        return events;
    }
}

MQTT Configuration

Create a local configuration as mosquitto.conf within the /etc/mosquitto/conf.d/ directory.

per_listener_settings true
pid_file /run/mosquitto/mosquitto.pid

persistence true
persistence_location /var/lib/mosquitto/

log_dest file /var/log/mosquitto/mosquitto.log

listener 1883
allow_anonymous true
password_file /etc/mosquitto/passwd

include_dir /etc/mosquitto/conf.d

Password setting

You create the password file using the command. This will create the user joule using the password/tenant pair within the passwd file.

mosquitto_passwd -b passwd joule joule/uk

Attributes schema

Attribute	Description	Data Type	Required
name	Name of source stream	String
broker	Broker server address	http://<ip-address>:port
topic	Message topic to subscribe too	Strings
clientId	A unique client identifier on the server being connected too	String
username	Username	String
password	password	String
tenant	Namespace for created topics	String
qos	Quality of service	Integer Default: 0
auto reconnect	Automatically reconnect to broker on disconnection	Boolean Default: true
clean restart	This means that if a client disconnects and reconnects within 5 minutes with clean restart=false,qos > 1 then session state data ( i.e. subscribed topics, queued messages) are retained	Boolean Default: true
sessionExpiry interval	Maximum time that the broker will maintain the session for once the client disconnects	Long Default: 300 (seconds) 5 minutes
registration message	Message to send to broker when a Joule process registers	String
user properties	Sets the user properties	Map<String, String>
connection timeout	This value, measured in seconds, defines the maximum time interval the client will wait for the network connection to the MQTT server to be established	Integer Default: 30 (Seconds)
keepalive interval	This value, measured in seconds, defines the maximum time interval between messages sent or received. It enables the client to detect if the server is no longer available, without having to wait for the TCP/IP timeout	Integer Default: 30 (Seconds)
lwt handler	Last Will and Testament message handler.	See Last Will and Testament page
deserializer	Deserialisation configuration	See Deserialisation attributes section
security	Security configuration	See Security documentation

Deserialisation attributes schema

This topic provides configuration parameters available object deserialisation process.

Attribute	Description	Data Type	Required
parser	User provided implementation	Implementation of StreamEventParser
compressed	Uncompress payload using Snappy	Boolean Default: false
batch	Flag to inform process multiple messages have been sent in payload	Boolean Default: false

Deserialiser example

In the given MQTT consumer configuration, the deserializer section defines how the incoming events should be processed and transformed before being consumed by the Joule platform.

1. parser The parser attribute specifies the class (com.fractalworks.streams.transport.mqtt.CustomerToStreamEventTranslator) responsible for converting the incoming message into a Joule StreamEvent object. This transformation is necessary to make the data compatible with the platform’s processing system.

2. compressed The compressed: false setting indicates that the incoming data is not compressed. If the data were compressed, this setting would need to be set to true and the system would decompress the data before processing.

3. batch The batch: false setting means that the events will not be grouped into batches for processing. Each event is processed individually as it is received. If set to true, it would allow the consumer to handle multiple events in a single batch, which can improve efficiency in some scenarios.

DSL

mqttConsumer:
  ...
  deserializer:
    parser: com.fractalworks.streams.transport.mqtt.CustomerToStreamEventTranslator
    compressed: false
    batch: false

Parser

import com.fasterxml.jackson.annotation.JsonRootName;
import com.fractalworks.streams.core.data.streams.StreamEvent;
import com.fractalworks.streams.core.exceptions.TranslationException;
import com.fractalworks.streams.sdk.codec.StreamEventParser;
import com.fractalworks.streams.transport.Customer;

import java.util.Collection;
import java.util.Collections;

@JsonRootName(value = "customer parser")
public class CustomerToStreamEventTranslator implements StreamEventParser {

    public CustomerToStreamEventTranslator() {
        // REQUIRED
    }

    @Override
    public Collection<StreamEvent> translate(Object o) throws TranslationException {
        Collection<StreamEvent> events = null;
        if(o instanceof Customer customer){
            StreamEvent event = new StreamEvent("customer");
            event.addValue("id", customer.getId());
            event.addValue("firstname", customer.getFirstname());
            event.addValue("surname", customer.getSurname());
            event.addValue("age", customer.getAge());

            events = Collections.singletonList( event);
        }
        return events;
    }
}

Additional resources

• Official Mosquitto documentation

• Good user documentation

• MQTT X UI for testing