Message Queues and more

Overview

• Messaging
  • Message Oriented Middleware
  • Enterprise Application Integration
  • Messaging models
• Messaging Standards
  • Java Message Service.
  • AMQP.
  • Other wired protocols.
• Provider Examples
  • ActiveMQ
  • RabbitMQ
  • Kafka

Messaging

Messaging

• Messaging – exchange of messages between client applications.

 

• Message – formatted data describing events, requests and replies.

Message Oriented Middleware

• Middleware - software components used to enable elements of a distributed system to communicate with each other.

 

• Message oriented middleware (MOM) – asynchronously working middleware that provides message-based communication between software components in a distributed system.

 

• MOM allows routing, transformation of messages to a different format and is asynchron, as opposed to other middleware paradigm, ORB and RPC. Components that communicate using MOM are loosely coupled.

 

• MOM requires at least one additional component in the system (so called message broker).

Enterprise Application Integration

• Combination of software and architectural principles intended to integrate a number of enterprise applications.
• Can be considered a middleware framework.

Messaging Models

• Message Queue
  • Relies on the idea of point to point communication.
  • Message will be deleted after it‘s read by one of the consumers.
  • Load balancing possible. According logic can be implemented in the message broker.

 

• Publish / Subscribe
  • Producers publish messages to different categories.
  • Subscribers consume messages from categories they are interested in.
  • Retention policy depends on implementation. (wait for every subscriber, fanout ignoring inactive subscribers or use time span for deleting messages).
  • Producers and consumers do not need to know anything about each other.

Messaging Standards

Java Message Service

Java Message Service (JMS) – is a message oriented middleware API that provides features and messaging concepts in order for software components to create, send, receive and read messages.

 

• Minimizes set of messaging concepts, yet supports creating sophisticated messaging applications.
• Each JMS compliant application is (1) Asynchronous and (2) Reliable
  • (1) – clients do not have to request messages in order to receive them
  • (2) – JMS API is able to ensure a messages is delivered exactly once. However, lower levels of reliability are also available.
• JMS supports both Message Queue and Publish / Subscribe paradigms.

JMS Elements

• Provider – a Java JMS implementation or an adapter to a MOM written in an other programming language.

 

• Producer – application or process that creates and sends messages

 

• Consumer – application or process that receives messages.

 

• Queue – storage that contains messages that have been sent, but not yet consumed. FIFO principle is not applicable here.

 

• Topic – storage or class of messages that are to be distributed to more than one consumer.

JMS Interfaces

• ConnectionFactory - provides functionality for creating connections for clients.
• Connection - channel between a client and the messaging service. It is thread safe and can usually be accessedby multiple clients
• Session - a serial order for producing and consuming messages. Should only be accessed by one thread at a time. Can be made transacted.
• Destination - represents the area (normally a remote one) for placing and acquiring messages. Either Queue or Topic. 
• MessageProducer - Represents a message's producer
• MessageConsumer - Represents a message's consumer
• Message - Root interface for JMS Message, that are further divided into types:

Advanced message queuing protocol

• Efficient flow control schemes.
• Different reliability levels.
• Flexible - can be used for different types of connection

Other protocols

• Simple Text-Oriented Messaging Protocol (STOMP)
  • HTTP Based, language-agnostic protocol.
  • Easy to use, yet supports many messaging features, like authentication, transactions, headers and properties and so on.

 

• Extensible Messaging and Presence Protocol (XMPP)
  • Xml based real-time extensible messaging protocol.
  • Used primarly for instant messaging and contact list maintenance. Newly also for IoT applications, gaming and other purposes.

 

• Message Queuing Telemetry Transport (MQTT)
  • Lightweight M2M / IoT publish/subscribe messaging protocol.
  • It is fast, reliable (TCP), simple in terms of putting and extracting payload.
  • Examples of usage: home automation, distributing data from smaller sensors to other devices.

Provider Examples

Example: ActiveMQ

• Supports many languages and protocols.

 

• Maintains the order of messages in a queue and dispatches them to consumer in order

 

• Fully JMS compliant

 

• Additional Features like Message Groups and Virtual Destinations.

Example: RabbitMQ

• User friendly admin interface, including useful monitoring tools.

 

• Extended plugin system.

 

• Flexible routing using different exchange types from AMQP 0.9.1.

 

• Clustering and Federation of messaging Servers.

Example: Kafka

• Positions itself as a distributed streaming platform.

 

• Very high throughput, even using moderate hardware.

 

• Supports partitioning of messages over messaging servers. A topic with N partitions will withstand N-1 server failures.

 

• Messages are called records, each having a key (header), value (payload) and a timestamp.

 

• Records are retained for a configurable time period. Allows for consumer to rewind and read same messages again. 

 

• Record is sent to consumer groups, while only one consumer inside a group gets it - enables load balancing and broadcasting. 

Thank you for your attention!