ApsaraMQ for MQTT:FAQ about client connections

Android Demo Reports 'Connection Failed' Error

Problem description

• The resources are correctly configured, and the network can be accessed.

• The AccessKey ID and AccessKey secret are authorized and correctly entered.

Possible cause

The format of the endpoint is incorrect. Specify the endpoint in one of the following formats: tcp://Endpoint:1883 or tls://Endpoint:8883.

Why can the client connect, but the consumer disconnects immediately upon subscription?

Why is the number of subscriptions that are displayed in the console higher than the number of subscriptions that are used in actual scenarios?

If the cleanSession parameter is set to false, the subscriptions are not cleared even after the client is disconnected.

If you do not want to retain subscriptions after the client goes offline, use the subscription cleanup feature to automatically clear offline client subscriptions.

Client Keeps Disconnecting and Reconnecting, and Returns "invalid param" Error.

Possible cause: The broker denied the connection request because the size of the message body exceeded the limit. In ApsaraMQ for MQTT, the size of a message body cannot exceed 64 KB.

Business side unchanged, client and server connection suddenly disconnects

Possible causes:

• A device shutdown or loss of network connectivity disconnects the client connection.

• If you use token-based authentication, the client disconnects after the token expires. If the client fails to obtain a new token before retrying the connection, the connection fails.

How do I specify the heartbeat timeout period of the client?

You can call the MqttConnectOptions class.

String clientId = mqttTools.getClientId();
mqttConnectOptions = new MqttConnectOptions();
// An Alibaba Cloud account AccessKey has permissions to call all APIs. We recommend that you use a Resource Access Management (RAM) user for API calls and routine O&M.
// Do not store the AccessKey ID in your source code. Doing so may lead to credential leaks and compromise all resources under your account.
// This example stores the AccessKey in an environment variable.
mqttConnectOptions.setUserName("Signature|" + System.getenv("MQTT_AK_ENV") + "|" + instanceId);
mqttConnectOptions.setPassword(mqttTools.macSignature(clientId).toCharArray());
mqttConnectOptions.setCleanSession(true);
// The heartbeat timeout period of the client. Default value: 90 seconds.
mqttConnectOptions.setKeepAliveInterval(90);
mqttConnectOptions.setAutomaticReconnect(true);
mqttConnectOptions.setMqttVersion(MQTT_VERSION_3_1_1);
mqttConnectOptions.setConnectionTimeout(5000);
mqttLogger.info("MQTT is connect setting={},clientId={}", JSON.toJSONString(mqttConnectOptions), clientId);
mqttClient = new MqttClient("tcp://" + endPoint + ":1883", clientId, memoryPersistence);
mqttClient.setTimeToWait(5000);
mqttClient.setCallback(this.getMqttCallbackExtended());
mqttClient.connect(mqttConnectOptions);

Client encounters 'valid owner failed' error when connecting

The device occasionally encounters a "connection reset by peer" error

When Client ID (ClientID) values are duplicated, the clients disconnect each other, causing the server to close the connection. If a client continues to send data over the TCP connection, it triggers the peer socket to send an RST packet.

You must ensure that the client ID you specify is globally unique. For more information, see Client limits.

How do I configure the automatic connection feature for the SDK for Java client in Message Queue for MQTT?

Enable the automatic client reconnection feature for the SDK for Java client

mqttConnectOptions = new MqttConnectOptions();
mqttConnectOptions.setAutomaticReconnect(true);

After you set the autoReconnect parameter to true, the Java SDK client in ApsaraMQ for MQTT automatically reconnects.

mqttClient.setCallback(new MqttCallbackExtended() {
            @Override
            public void connectComplete(boolean reconnect, String serverURI) {
                /**
                 * The topic that you must subscribe to after the client connection is established.
                 */
                System.out.println("connect success");
            }

            @Override
            public void connectionLost(Throwable throwable) {
                throwable.printStackTrace();
            }

            @Override
            public void messageArrived(String s, MqttMessage mqttMessage) throws Exception {
                /**
                 * The callback that is called to consume messages. Make sure that the callback does not throw exceptions. If the callback returns, the message is consumed.
                 * Messages must be consumed within the specified time. If consumption takes longer than the timeout period set by the broker, the broker may resend the message in reliable transmission mode. Make sure that your business logic handles duplicates.
                 * For information about the timeout period, see Limits.
                 */
                System.out.println(
                    "receive msg from topic " + s + " , body is " + new String(mqttMessage.getPayload()));

            }

            @Override
            public void deliveryComplete(IMqttDeliveryToken iMqttDeliveryToken) {
                System.out.println("send msg succeed topic is : " + iMqttDeliveryToken.getTopics()[0]);
            }
});

When the connectComplete method in the client callback is invoked, the connection or reconnection becomes successful. You do not need to monitor the connection status. The re-established connection is different from the previous one. Therefore, actions such as sending or subscribing to messages on the previous connection no longer take effect.

At this point, you must resubscribe to the topic so that the business side can continue to send subscription messages over the new internal connection.

@Override
public void connectComplete(boolean reconnect, String serverURI) {
    /**
    * The topic that you must subscribe to after the client connection is established.
    */
    System.out.println("connect success");
    executorService.submit(new Runnable() {
        @Override
        public void run() {
            try {
                final String topicFilter[] = {mq4IotTopic};
                final int[] qos = {qosLevel};
                mqttClient.subscribe(topicFilter, qos);
            } catch (MqttException e) {
                e.printStackTrace();
            }
        }
    });
}

Manual client connection maintenance on the application side

mqttConnectOptions = new MqttConnectOptions();
mqttConnectOptions.setAutomaticReconnect(false);

If the autoReconnect parameter is set to false, the ApsaraMQ for MQTT client does not automatically reconnect after it is disconnected.

When the connection is lost, the business side detects an abnormal condition. You must manually shut down the legacy connection and then establish a new one.