I feel the importance of Queues as a communication medium between Web and worker roles is quite a bit under-glorified…apart from acting as reliable messengers , if implemented properly Queues pretty much hold the key to your application being Extensible and Scalable
Windows Azure Queue allows decoupling of different parts of a cloud application, enabling cloud applications to be easily built with different technologies and easily scale with traffic needs.
This above definition is full of some very important keywords..decoupling.…different technologies…. scale with traffic needs…all very important to make a scalable and extensible application..
Lets see how Queues help in all these aspects.
- Observing the queue length and tuning the number of backend nodes accordingly, applications can effectively scale smoothly accordingly to the amount of traffic. A growing queue length or an almost always zero queue length is an indication of how loaded your worker roles are and you might want to scale them up or down accordingly
- The use of queues decouples different parts of the application, making it easier to scale different parts of the application independently. This allows the number of web and worker roles to be adjusted independently without affecting the application logic.
- Separate queues can be used for work items of different priorities and/or different weights, and separate pools of backend servers can process these different queues. In this way, the application can allocate appropriate resources (e.g. in term of the number of servers) in each pool, thereby efficiently use the available resources to meet the traffic needs of different characteristics
- Different technologies and programming language can be used to implement different parts of the system with maximum flexibility. For example, the component on one side of the queue can be written in .NET framework , and the other component can be written in Python.
- Changes within a component are transparent to the rest of the system. For example, a component can be re-written using a totally different technology or programming language, and the system still works seamlessly without changing the other components, since the components are decoupled using queues. The old implementation and the new implement can run on different servers at the same time, and process work items off the same queue. All these are transparent to the other components in the application
But to be able to achieve all these benefits you need to make sure your queues are implemented in the most optimal way . There are a lot of best practices around Queue implementation such as Invisibility Time, Delete queue messages, Worker role instance manipulation etc…more on that some other time…meanwhile if you want more inputs on “Queueing your way to scalability” drop us a a note at Cennesttech@hotmail.com..