Configuring Transports for the Broker

The Message Broker profile of WSO2 EI uses two transport protocols for the purpose of brokering messages between publishers and subscribers. These protocols are the Advanced Message Queueing Protocol (AMQP) and the Message Queueing and Telemetry Transport (MQTT).

The following topics explain how these protocols are enabled and configured for the Message Broker profile:

Advanced Message Queuing Protocol (AMQP)

The Advance Message Queueing Protocol (AMQP) is a wire-level messaging protocol used for message queueing. The <EI_HOME>/wso2/broker/repository/conf/broker.xml file contains parameters related to configuring the AMQP transport. 

Enabling the transport

The AMQP transport is enabled by default, as shown in the following extract of the broker.xml file:

<amqp enabled="true">
	<defaultConnection enabled="true" port="5672" />
</amqp>

As shown above, if the value of this parameter is true, the AMQP transport is enabled and the AMQP protocol will be applied to messages sent to the specified listening port. The default listening port specified for the AMQP transport is 5672. That is, the AMQP broker will be initialized with this port by default. This value will be incremented based on the offset specified in the carbon.xml.

Configuring the SSL connection

You can configure a SSL connection for the AMQP transport using the <sslConnection> element in the broker.xml file. See Enabling SSL Support in the Broker for information.

Related Parameters

Once you have enabled the AMQP transport, you can update the following related parameters as required.

<amqp enabled="true">
	............
    <maximumRedeliveryAttempts>10</maximumRedeliveryAttempts>
    <allowSharedTopicSubscriptions>false</allowSharedTopicSubscriptions>
    <allowStrictNameValidation>true</allowStrictNameValidation>
	............
</amqp>

Message Queueing and Telemetry Transport (MQTT)

The Message Queueing and Telemetry Transport (MQTT) is a lightweight, broker-based publish/subscribe messaging protocol, which enables an extremely lightweight publish/subscribe messaging model. The Message Broker profile of WSO2 EI fully supports MQTT version 3.1.0, and partially supports version 3.1.1.

The MQTT protocol allows a message to be sent to a topic based on three levels of QoS (Quality of Service) as explained below.

• QoS 1 - At Most One - At this level, messages are delivered to subscribers in the most efficient manner. A message is dispatched only once.
• QoS 2 - At Least One - At this level, the system will ensure that a message is received by the subscriber at least once. The level of delivery is assured through acknowledged delivery.
• QoS 3 - Exactly Once - At this level, the message is delivered only once to its subscriber. This level is also defined as Assured Delivery.

Just as the AMQP transport, the MQTT transport can be configured using the <EI_HOME>/wso2/broker/repository/conf/broker.xml file.

Enabling the transport

The MQTT transport is enabled by default, as shown in the following extract of the broker.xml file:

<mqtt enabled="true">
	<defaultConnection enabled="true" port="1883" />
	.......
</mqtt>

As shown above, If the value for this parameter is true, the MQTT transport is enabled and the MQTT protocol will be applied to messages that are sent to the specified listening port. The listening port for the MQTT transport is 1883. The MQTT broker will be initialized with this specified port by default. This value will be incremented based on the offset specified in the carbon.xml.

Configuring the SSL connection

You can configure a secure SSL connection for the MQTT transport using the <sslConnection> element in the broker.xml file. See Enabling SSL Support in the Broker for information.

Configuring authentication and authorization

Authentication and authorization of the MQTT connection can be configured using the following settings in the broker.xml file.

<mqtt enabled="true">
	..............
    <security>
             <authentication>OPTIONAL</authentication>
             <authenticator>org.wso2.carbon.andes.authentication.andes.CarbonBasedMQTTAuthenticator</authenticator>
			 <!--authenticator class="org.wso2.carbon.andes.authentication.andes.OAuth2BasedMQTTAuthenticator">
                <property name="hostURL">https://localhost:9443/services/OAuth2TokenValidationService</property>
				<property name="username">admin</property>
				<property name="password">admin</property>
				<property name="maxConnectionsPerHost">10</property>
				<property name="maxTotalConnections">150</property>
			</authenticator-->
			<authorization>NOT_REQUIRED</authorization>
			<authorizer class="org.wso2.carbon.andes.authorization.andes.CarbonPermissionBasedMQTTAuthorizer">
				<property name="connectionPermission">/permission/admin/mqtt/connect</property>
			</authorizer>
    </security>
</mqtt>

The above configurations are explained below:

• The <authentication> element instructs the MQTT server on whether clients should always send credentials when establishing a connection. Possible values are as follows:

  OPTIONAL	This is the default value. If an MQTT client sends credentials, the server will validate them. If the client does not send credentials, the server will allow the client to establish the connection without authentication. This behavior adheres to the MQTT 3.1 specification.
  REQUIRED	If the MQTT client doesn't send credentials or if the credentials are invalid, the server will reject the connection. Note that if authentication is REQUIRED, the permissions linked to the credentials may also be checked depending on the value specified for <authorization> element.

• The <authenticator> element specifies the class that implements authentication. By default, the org.wso2.carbon.andes.authentication.andes.CarbonBasedMQTTAuthenticator class is enabled, which authenticates the user's credentials against the Carbon user store.

  If required, you can disable the default authenticator and enable the org.wso2.carbon.andes.authentication.andes.OAuth2BasedMQTTAuthenticator authenticator class as shown below. This class enables OAuth-based authentication and authorization for MQTT.

  <mqtt enabled="true">
  	..............
      <security>
               .........
  			 <authenticator class="org.wso2.carbon.andes.authentication.andes.OAuth2BasedMQTTAuthenticator">
                  <property name="hostURL">https://localhost:9443/services/OAuth2TokenValidationService</property>
  				<property name="username">admin</property>
  				<property name="password">admin</property>
  				<property name="maxConnectionsPerHost">10</property>
  				<property name="maxTotalConnections">150</property>
  			</authenticator>
  			......
      </security>
  </mqtt>

• The <authorization> element instructs the MQTT server on whether clients should have permission to publish messages to the broker or to subscribe to the broker. Possible values are as follows:

  NOT_REQUIRED	This is the default value. The MQTT client does not require permission for the purpose of publishing messages or to subscribe.
  REQUIRED	The permissions granted to the MQTT client will be checked before allowing the client to publish messages. This check will execute the class given in the <authorizer> element that is explained below. Note that the <authentication> element should be set to REQUIRED for authorization to be REQUIRED.

• The <authorizer> element specifies the permissions required by a user to connect to the broker. This is applicable if the <authorization> element is set to REQUIRED.

  <mqtt enabled="true">
  	..............
      <security>
               ........
  			<authorizer class="org.wso2.carbon.andes.authorization.andes.CarbonPermissionBasedMQTTAuthorizer">
  				<property name="connectionPermission">/permission/admin/mqtt/connect</property>
  			</authorizer>
      </security>
  </mqtt>