Introduction
A robust, reliable, scalable, secure, compatible and maintainable system is the key to the success for the business.
Using a middleware for messaging gives the software development loosely coupled, more flexible and easy to scale and maintain.
Apache ActiveMQ is a message broker (middleware) for remote communication between different systems in different environment. Although ActiveMQ is written in Java, it supports many protocols and provides APIs for many other languages, including C/C++, .NET, Perl, PHP, Python, Ruby and more. It can be seen as a general messaging solution for a variety of development platforms.
It provides high performance, reliability, scalability, security, compatibility, and maintainability. In this document, I will overview these areas.
Concepts
Before going through those areas, here are the concepts used in the document.
*Producer - Message generator which has a one-to-one relationship with consumer
*Consumer - Message receiver which has a one-to-one relationship with producer
*Publisher - Message genertor which has a one-to-many relationship with subscribers
*Subscriber - Message receiver who receives publisher's messages
*Queue -A Queue implements point-to-point (PTP) messaging semantics. A single message will be received by exactly one consumer. If there are no consumers available at the time the message is sent it will be kept until a consumer is available that can process the message.
*Topic - A Topic implements publish and subscribe semantics. When you publish a message it goes to all the subscribers who are interested.
*Broker - A server delivering messages
*Destination - A unique identifier for sending and receiving messages.
Performance
ActiveMQ offical test produces 21-22,000 messages/second for 1-2K data delivery [1]. I test on my machine, it delivers about 7,000/second [2]. Of course, the broker, consumer and producer are all in the same machine.
According to ActiveMQ, a single broker can handle over 10,000 concurrent users, even just using ajax approach (jetty as its underline technology) [3].
Reliability
ActiveMQ provides several mechsnisms to ensure reliable message delivery. It has failover configuration, which has a master broker and slave brokers backup. Once the master broker fails, one slave takes over the role to become a master to continue message delivery.
It can be done by only one line xml configureation as following:
failover://(tcp://masterhost:61616,tcp://slavehost:61616)
It also provides message cache to ensure a message is delivered to the consumer when the consumer's connection is temporarily failed for some reason, such as mobile connection lost signal.
This configuration uses a XML format configurable policy for deciding which types of messages should be cached, how many and for how long.
You can even configure more complicated broker networks to have local and remote master, local and remote slave.
Scalability
ActiveMQ provides three ways to scale the messaging system, Vertical, Horizontal scaling and Traffic Partitioning.
The vertical scaling will improve connections and numbers of Queues on a single broker to achieve thousands of connections and Queues. The horizontal scaling will increase the number further to ensure tens of thousands of connections concurrently. Finally the traffic partitioning will balance scaling and performance.
Vertical Scaling
Vertical scaling increases the number of connections and load on a single ActiveMQ broker, so the borker can handle both a large number of concurrent connections and a large number of Queues.
By default, ActiveMQ will use blocking I/O to handle transport connections, which results in one thread per connection. ActiveMQ can be configured to use Non-blocking I/O, which creates a thread pool for dispatching messages for multiple client connections.
You can also control memory size allocation through configuration to ensure there is enough capacity for large traffic.
The default Queue configuration uses a separate thread for paging messages from the store into the Queue to be dispatched. For a large number of Queues, you can disable this to avoid out of memory.
Horizontal Scaling
Apart from scaling a single broker, you can use a broker cluster network to increase the number of ActiveMQ brokers available for a busy system.
As the network automatically pass messages to connected brokers that have interested consumers.
Traffic Partitioning
ActiveMQ also provides an application level splitting of destinations, or traffic partitioning. The client application decides what traffic should go to which broker(s).
Security
Apart from basic authentication to use ActiveMQ. It also provides two level of authorization, operation level authorization and message level authorization.
Operation Level Authorization
It defines three roles, Read, Write, and Admin.
- Read - The ability to receive messages from the destination
- Write - The ability to send messages to the destination
- Admin - The ability to administer the destination
Message Level Authorization
In some situations you might want to authorize access to only particular messages in a destination. You can create a message level authorization, which will check if the consumer has the right to receive certain messages.
Broker Level Operations
Broker operations includes such items as adding consumers and producers to the broker, committing transactions in the broker, adding and removing connections to the broker, etc. This gives the flexibility for clients to add their whitelabels.
Compatability
ActiveMQ supports many different transport protocols HTTP, HTTPS, SSL, Websocket, TCP, and many message protocols, Openwire, REST, RSS, XMPP, STOMP(Streaming Text Orientated Messaging Protocol). For instance, the server-side publishes messages via TCP, the front-end can choose HTTPS or Websocket to connect to the broker. This gives many choices for the clients to use depending on their environment. On the message protocol, for example, a C++ or Java client can use high performance binary protocol, Openwire, to send/receive messages, while, for scripting languages, such as PHP, Python, can use STOMP.
Mantanability
ActiveMQ provides messaging support system. You can monitor how many consumers are currently connected. How many messages are received and delivered.
It has Advisory messages, which are system messages generated by brokers. Typically, an advisory message will be generated every time a new administered object (Connection, Destination, Consumer, Producer) joins or leaves the broker. It can also report a warning about the ActiveMQ broker reaching system limits.
References
[1] ActiveMQ performance http://activemq.apache.org/performance.html
[2] JMS (ActiveMQ) Performance Verification http://liukeye.blogspot.com/2010/10/jms-activemq-performance-verification.html
[3] Jetty Continuations http://docs.codehaus.org/display/JETTY/Continuations
