Architecture Design Patterns: Key Strategies, Decisions, and Documentation for Effective Software Architecture

Design patterns and implementation strategies are essential components in software architecture, providing conceptual solutions to recurring design problems and guiding the development process. By understanding and applying these patterns, architects can address primary requirements, constraints, and quality attributes effectively. This article explores the significance of design patterns, the strategic decisions involved in their implementation, and the importance of thorough documentation to ensure successful project outcomes.

Design patterns:

Are conceptual solutions to repeating design problems and typically have a defined context. We shall consider a pattern to be architectural when its use substantially satisfies some of the architectural drivers (primary requirements, constraints, quality attributes etc). For example, an architectural pattern that is useful for structuring the system, is the Layers pattern. To use it, you must decide how many layers are needed, or to increase performance you may use a pattern to support concurrency (async processors etc) - Which pattern and how to use, depends on the problem context.

A reference architecture may be considered a pattern, but it itself may contain other patterns, like a reference architecture for a web-application is preferred to have layers (presentation, biz-logic, data-access+storage, services etc), and have concerns like security, interactions etc to address.

Design implementation strategies:

To achieve performance, for example, one can use some strategies - either manage resources or constrain their usage by a single thread/user etc. Constraining usage may include restricting requests for resources somehow. Managing resources may include one or a combination of the following: increasing resources (horizontally and/or vertically), use concurrency, load-balanced cluster, distributed data & computation etc. Similarly, there are few strategies to achieve other quality attributes.

Do you design & build every tool you need: Not really. Some tools are taken-as-is like Databases, 3-party commercial or open-source products, application frameworks (ie spring/hibernate...), development language/platform etc. If you are in the software industry for long enough, you can understand why. But here are typical factors that affect their selection: its cost/license, support provided or not, problem it solves, its learnability, is it popular and mature enough, easy to integrate, quality attribute SLAs etc. These are also the questions that affect the decision whether to build in-house or use an external one.

Design decisions:

Is it enough to choose an architectural/reference pattern, or does an architect still need to make more decisions?

For example, think about a layered architecture: how many layers? How tightly coupled? Which service/s go into which layer, interfaces b/w layers etc.
Or for a clustered deployment pattern: how many servers needed? Session affinity needed? How will fail-over happen? Where is the load-balancer and servers going to reside from security perspective (ie DMZ etc)? Encryption needed b/w LB and servers? How will the server monitoring, maintenance, updating etc happen?

You see, the answers to all of these questions should come from the architect to ensure successful implementation of the project.

Design Documentation:

Once an architecture is chosen, other required decisions are taken, it comes to documenting them. There is no rule or standard practice on how to perform this activity, but no documentation is generally a bad practice and results in future problems. Architect should document the decisions, analysis (supporting why/how some choices and decisions were made), tools/framework etc choices and so on, and may choose to write in plain English or with sketches or formal diagrams (ie UML etc).

In conclusion, design patterns and implementation strategies are vital in shaping robust software architecture. By leveraging these patterns, architects can effectively address recurring design challenges, meet primary requirements, and adhere to constraints and quality attributes. Strategic decisions in pattern implementation, coupled with thorough documentation, ensure that projects are executed successfully and maintainable in the long term. The careful selection of tools and technologies, guided by factors such as cost, support, and integration ease, further enhances the development process. Ultimately, a well-documented and thoughtfully designed architecture lays the foundation for a successful software project.