The word "system architect" has been puzzling to me. I was hired to be one at one point. But it was not a comfortable position. How much do we understand the business? What is the problem we are to solve? How does the current "architecture" fail? What is the downfall of this (or any) proposal? Overall, I feel an architecture emerges along with development and research. The more we start to understand the client's needs, habits, workflows, relationships, priorities, the more information we have when evaluating and making decisions on whether one piece in the stack fits or not, and why so. It is, IMHO, a backwards process when an architecture is pre-defined as if it is set in stone. We need to start from somewhere, but keeping in mind that it evolves and shifts like a living organ.

    System architecture evolves and shifts like a living organ.

    This is a system architecture I have been using recently in projects. It is divided into four components:

    1. foreground service provider: this includes machinery that interface with web server, taking HTTP and AJAX requests, and generate response to request. The core of this component is Python Django. Django is chosen for its reputation, for my past experience, for its maturity, excellent documentations and a broad user base. Backed by Python, it is a great starting point for building a web application.

    2. background service provider: it handles all code executions that do not need be in synchronous fashion with a user request. The key here is task queue integrated using Celery with Redis or RabbitMQ. These replaced what used to be messy multithreading code that were prone to error and hard to debug. Besides, architecture wise these message queues extend well, so it's a natural fit for cloud deployment.

    3. data storage service: traditional RDBMS and file system. A consideration here is certainly to include remote storage such as AWS. The key point is to separate static data (style sheets, JS scripts, media files) from dynamic application data. A side note. I think the distinction is rather misleading since most application data become stale(static) also once generated, and many image data nowadays are saved in DB (so system backup takes one step instead of two). Both have its use.

    4. integration service: customized code to implement third party system integration. In general, CRUD operations are handled through frontend API(REST) service. There is also so called backdoor tasks that covers cases where data may get pumped directly into data storage via ORM layers. Such cases may include initial data import, runtime data synchronization, data extraction and system backup.

    Feng's system architecture diagram

    The beauty of this architecture is that message queue becomes a distribution hub where tasks are dispatched to different destination end point for processing. This greatly reduces the complexity of inter- and intra- system communication. Knowing that queue servers can be easily extended if load become heavy is yet another benefit to have in term of scalability.

    As shown in the diagram, background queue tasks are being used solely to generate and consume model data (including media data since media has always some meta data components). This means they do not participate to generate inline view response. Instead, they take instruction from user input and distribute those intensive code for asynchronous processing. This remedies Django's synchronous nature (I say it is synchronous in the sense of that a Django's native process will receive and process view request without interrupt or callback. Django signals are asynchronous, however.) where a long running code section could bring the entire application to halt.

    — by Feng Xia


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