MQTT in Reactive Blocks
- 1. MQTT A summary of MQTT and how to use it in Reactive Blocks Publish/Subscribe via in Reactive Blocks
- 2. MQTT: Overview ■ MQTT is a protocol on top of TCP/IP to send messages via a broker, using a publish/subscribe pattern. ■ OASIS standard since November 2014 ■ More info on http://mqtt.org ■ Alternatives to MQTT include HTTP, AMQP and CoAP ■ MQTT is typically used to send event data from gateways to a backend, and commands from a backend to a gateway By default, MQTT uses port 1883 or port 8883 (secured). Make sure that traffic via these ports is not blocked by your firewall. Ports With MQTT, clients can be behind a NAT without problem. The clients initiate an outgoing TCP connection over which the server may reply. NAT !
- 3. A subscriber connects to a broker and subscribes to one or more topics. Once a publisher sends a message to a topic, all subscribers that subscribed to that topic are notified and will receive the message. Several publishers may send to the same topics. Several subscribers may subscribe to the same topics. Publish/Subscribe Pattern publisher broker subscribe (topic) subscriber publish (topic, payload) message (topic, payload)
- 4. Topic Structures ■ Each message is published with a specific topic. A subscriber listens to one or more topics. The broker forwards a message to all subscribers with a matching topic ■ There is no predefined topic structure in MQTT. Publisher and subscriber simply need to agree on a topic structure. ■ Topics can be structured into different levels, separated by a “/“. Chosen wisely, the topic structure can help the receiver to filter messages it wants to receive. ■ The number sign “#” matches any number of levels. The plus sign “+” matches exactly one level. 4
- 5. Topic Example ■ 5 By using topics systematically, receivers may filter which messages they want to receive. The following topic structure is an example: iot/type/<device-type>/id/<device-id>/event/<event-id>/format/<format-ID>/ (The segments in brackets are replaced by specific strings for each message.) A receive may select to receive all events sent by gateways of type “raspberry” by subscribing to the following topic: iot/type/raspberry/id/+/event/+/format/+/ A receiver may select to receive all “temperature” events sent in json format, to any device of any device type: iot/type/+/id/+/event/temperature/format/json
- 6. March 2012 - Business Confidential - Bitreactive AS How to get started MQTT in Reactive Blocks
- 7. Install Reactive Blocks ■ In Eclipse 4.4 or Eclipse 4.5, open the Marketplace ■ Search For Reactive Blocks ■ Also install the Feature Reactive Blocks for OSGi ■ For detailed installation instructions, visit http://www.bitreactive.com/installation/ 7
- 8. How to Get This Library ■ After installing Reactive Blocks ■ In Eclipse, select File / Import / Reactive Blocks / Import Libraries, Projects and Building Blocks ■ Select the library MQTT Feature 8 In the following, we describe how to use the OSGi version of our building block library for MQTT. OSGi!
- 9. MQTT Client Configures and manages the MQTT connection. This block is required. Messages are only sent and received while it is active. Building Blocks for MQTT Subscribe Subscribes to a topic (or list of topics) and receives the messages sent to that topic. To subscribe to more than one topic, use several instances of this block. Publish Send messages to a certain topic. You can use more than one instance of this block.
- 10. March 2012 - Business Confidential - Bitreactive AS Advanced Features
- 11. Quality of Service ■ 0… at most once: Delivery is not guaranteed, no retry. For streaming data where one individual event is not important. ■ 1… at least once: Delivery is guaranteed, but the message can be duplicated. ■ 2… exactly once: Message is sent exactly once, but at with a higher overhead. ■ By default, QoS of a message is 0. To change it, set the QoS flag in the message before you send it. 11 Messages can be sent with a certain quality-of-service, which depends how much effort the protocol spends to deliver it.
- 12. Retained Messages ■ A sender may mark a message as “retained”. ■ A retained message is kept on the server. ■ As soon as a client subscribes to a topic that matches the retained message, it will receive the retained message. 12 publisher broker subscribe (topic) subscriber publish (topic, payload) message (topic, payload) «retained» Note that the subscriber subscribes after the message was sent. ■ To retain a message, mark it as retained with the API before sending it.
- 13. Automatic Reconnect: The MQTT subsystem maintains the connection and reconnects in case the connection goes down. Reconnect works either immediately or after a timeout that increases with each failed connection attempt. Messages with qos 0 are discarded while the connection is down. Persistence: Messages with qos>0 are buffered until they are sent. By default, the buffer is in memory only. To use a file buffer, set the flag and choose the file name in the parameters object. Time-to-live: Messages can have a time- to-live value, after which they are discarded. By default, messages do not time out. Security: By default, MQTT uses TCP as protocol and the payload is sent in clear text. To use TSL, set the flag useSecureConn() in the parameters object. If the broker requires a username and password, use the corresponding methods in the parameters object. MQTT Features When using the building blocks, the following features are available. You can configure them with the parameters objects passed to the MQTT Client block.
- 14. Multiple Connections ■ You can simultaneously maintain several MQTT connections, either to the same or towards different MQTT brokers. ■ The separate connections can be configured individually (persistence, ttl, security) ■ Each connection is identified with a multiton-Id, set as instance parameter on each block. ■ Blocks with the same multiton-Id belong to the same connection. 14