Designing enhancements

Software architecture is needed for enhancements too

We're enhancing one of the software systems that I'm involved with, where we're adding new functionality into some of the existing use cases. If you imagine that these use cases are implemented by the users working through a number of pages in a web application, we're basically modifying the final step across a number of them.

So then, the system is being modified from the user's perspective because they are going to see some changes in the way that they use the system. While this itself isn't architecturally significant, we are interfacing with a brand new system behind the scenes. Typically, system enhancement projects require a very light architecture touch but this one needs slightly more because of the nature of it.

Interfaces are usually one of the more risky elements of software projects, particularly when you're consuming an interface that you don't have control of, as is the case here. Furthermore we're doing something that hasn't been done in the existing architecture, which is interfacing with a third party over the Internet. From a coding perspective it's easy because we're just opening up a HTTPS connection and throwing some XML data down it. Where it starts to get tricky though is with our deployment infrastructure because our servers need to punch through the firewalls to reach the outside world.

Although an enhancement to an existing system, this is one of those projects that benefits from some architectural input. Rather than dive straight into the code, it's important that somebody steps back to look at the bigger picture elements such as:

  • Design and how best to integrate the new functionality.
  • The definition of the interface and whether it's synchronous or asynchronous, the protocol, the message format, etc.
  • Confidentiality of sensitive user information and ensuring service credentials remain secure after deployment.
  • How the changes affect the existing infrastructure from a security perspective.
  • How the new functionality will meet existing audit requirements.

This is no different from what you'd do at the start of a software project, but it highlights that architecture is often necessary at other stages during a system's lifetime. Next time I'll discuss how we phased the delivery of this enhancement to evaluate our architectural decisions early.

About the author

Simon is an independent consultant specializing in software architecture, and the author of Software Architecture for Developers (a developer-friendly guide to software architecture, technical leadership and the balance with agility). He’s also the creator of the C4 software architecture model and the founder of Structurizr, which is a collection of open source and commercial tooling to help software teams visualise, document and explore their software architecture.

You can find Simon on Twitter at @simonbrown ... see for information about his speaking schedule, videos from past conferences and software architecture training.

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