Amazon continue its relentless release of new Cloud Computing services with the release of the Simple Workflow Service (SWF). This sophisticated service enables distributed asynchronous applications to be implemented as workflow. A workflow is built from three core components:
- Workflow starters
- Activity workers
- Deciders
Workflow starters initiate the workflow. This can be any application. The classic example is a customer placing an order on an e-commerce site starting a workflow that completes with a shipped order and includes all the intermediate stages including payment processing, stock allocation and shipping.
Activity workers are the threads that perform the tasks required by the workflow. These are written by the software developers, in potentially any programming language, and can run anywhere (on-premise or cloud hosted) as long as they can access SWF through the provided API.
Deciders implement the workflows decision logic. The deciders look at the workflow history to determine what has been completed and make a decision as to what to do next.
With the release of SWF, Amazon have provided an elegant solution to a difficult problem: how to build applications that make use of a number of distributed components that can be a mixture of on-premise and cloud hosted and monitor and co-ordinate them in a reliable and scalable manner.
What I like about Amazon AWS in general is that they make it straightforward to use. With SWF, then the service addresses an area that is complex and yet Amazon have provided a clean elegant solution. I look forward to using it soon.
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