Thursday, June 11, 2009

A Sinfonia on Messaging with txAMQP, Part II

A Sinfonia on Messaging:
  1. The Voice of Business
  2. The Voice of Architecture
  3. A RabbitMQ and txAMQP Interlude

After writing the last blog post, I found a fantastic site that focuses on messaging in the enterprise. I have really enjoyed the big-picture overview I get from some of the Martin Fowler signature books in this series, so I ordered a copy of this one too.

On the web site, the authors give a nice example for messaging integration in Chapter 1. They provide a more detailed, supplier-version of the kilt store (we're doing "manufacturing" as opposed to distribution) with "Widget-Gadget Corp", but the basic principles are the same. I highly recommend reading that entire page. I used it as the basis for much of this post.

Business Process Overview

At a top-level, we have the following business process for MacGrudder's kilt store:

These are represented by a sales guy or a web store, a third-party billing service, MacGrudder, and a third-party shipping service.

Up until now, the sale process could be either a user deciding to buy something in the online store or the sales guy engaging with a customer. Both generated orders; neither shared resources. The web app interfaced with the payment gateway operating by billing/shipping guy. The sales guy had to call in his orders to the billing/shipping guy. Once orders were charged/approved, a printout was handed to MacGrudder, who then created the ordered kilt. Once completed, he'd set it aside for shipping guy to come box it up and slap a label on it.

The Voice of Architecture

We're now ready to weave in the second voice of our three-part invention. MacGrudder's original infrastructure consists of silos of applications, functionality, data, and process. We want to interconnect these separated areas in order to reduce long-term overhead incurred by redundant components and data. Practically, we want to see the following changes:

Unified orders: at the end of the sales process, there should be one abstraction of the "order", regardless if the source was the web store, a phone call, or the sales guy. The order abstraction will be a message (or series of messages, for orders with multiple items; we'll be addressing only the simple case of a single item).

Unified validation and billing
: at the end of the order creation process, there should be a validated order or an invalid order (e.g., if there were insufficient funds). At the end of the billing process, there should be an approved order that has be paid for via a single means (e.g., a single payment gateway, without bothering billing guy for manual entry). Additionally, once an order has been validated, messages should be sent to other components in the system.

Unified status: at the end of the manufacturing process, both the shipping guy and customers should be aware that the product has been completed and is ready to be sent: the shipping guy can connect to our messaging system (probably via a service) and the customer can be notified by email or by checking the order status in the web kilt store.

In the next installment, we will finally start looking at the code. We'll look at the "unified orders" messaging solution after covering some basics with RabbitMQ and Twisted integration, and then see how far we get with implementation details and descriptions. Unified validation, billing, and status might have to be pushed to additional posts.


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