DDD is not a goal but a means

DDD (Domain-Driven Design) it is “only” one essential building block that promises an evolutionary software, a software that won’t let you down in a few years or after a few thousands of line of code.

That’s it. I could stop here, the title and this short description tell everything. But is this true, can everybody reading this relate to that? Is it helpful? I don’t think so.

During the last year, I often heard the question “how can I introduce DDD in my company?” – mostly meaning “in my dev team”. It is time to answer this question now.

Misconception number 1: introducing DDD as a goal

Misconception number 2: DDD is a dev thing, and after the devs “fix this” by applying all the patterns, all problems will disappear – and they will live happily ever after …

Let’s imagine a successful company sitting already on 1m lines of code, a lot of customers, a few teams, possibly working in silos, having frontend and backend development split. Or a younger company but with the same organization, the only difference is the effort needed to change things. This company has an agile development process (with sprints and “stories” and one Product Owner pro team etc.), but they observe that every new feature takes longer and longer. A few devs have read about DDD, read the Blue Book, and convince one of the backend teams to introduce DDD. The company agrees to let them do it because they hope that everything will be easy and fast and bug-free afterwards. So everybody is happy 😊

Fast-forward a few months: now we are at the point when the source code owned by that team was restructured nicely, with value types, entities, aggregates. Ok, the Rest API is unchanged because the frontend team is already using it and they were not involved. But the business logic ist cleaned up. The names, the language were defined by the devs – DDD is a dev thing, isn’t it? The development process didn’t change either: they get requirements to implement things without including anything built by the frontend team, the part the customer sees. For this reason, the refinements are not about customer needs but API calls and frameworks – just like before the rework towards DDD.

JIRA 1234: Please add this new flag “withVAT” to the API call generating the invoice (sounds familiar?)

What is new? Frustration: the PO does not know why the devs are asking more and more details, and the developers don’t understand why the PO does not get the meaning of aggregates and value types, etc.

Refinement: “we cannot add it to that API call, the VAT decision belongs to another aggregate! ;( ”

And what else is new? Maintaining those API routes becomes harder and harder because they do not follow the business structure but are kept as an Anticorruption Layer between the frontend and backend (team 😉).

I am sorry if I am disappointing you, it is not my intention. It is the opposite actually: to save you from this frustration after having invested so much energy and maybe extra hours to get everything perfect.

What is DDD: a paradigm, a rule set that helps you to build an evolutionary software. Like Mathias Verraes says

This can only be achieved if DDD stops being a “dev-stuff” and starts leading to a common way to discuss features, behaviors, and capabilities.

And why not? DDD means not only aggregates and value types; the essential component is the ubiquitous language used in your domain by the business people, by the customer. And apropos customer: DDD aims to solve the customer’s problems and be known in the teams applying DDD. Why not create a whole team handling those needs, from the UI (or even UX) to the delivery? (this move would also change the “somehow agile” development process in a real one, based on feedback and experiments instead of a prepared backlog covering the next three months)

We live in a great time: the accumulated knowledge and the evolution of the software industry in the last 25 years give us anything we need to build resilient, sustainable and maintainable software that won’t “die” slowly if we are careful and happy to learn. What do we need?

  1. Visual modelling technics to discuss and learn the business (like Event Storming, Impact Mapping, etc.)
  2. Crunching and defining stories aiming to solve customer needs, always with the Ubiquitous Language (like User Story Mapping, BDD)
  3. A paradigm to make decisions based on the Business Domain, not on hopes or wishes (strategical DDD to write the right code)
  4. A guide for organizing the teams to achieve good teamwork, less cognitive load and smooth development process (Context Maps from DDD)
  5. Open feedback culture to create psychological safety
  6. A set of patterns to organize the code (DDD again)
  7. A bunch of practices to write the code right: TDD, refactoring, pairing, mob-programming
  8. Trunk-based development (aka Continuous integration) and continuous delivery to reduce the lead time (the time from the idea to the usage, also to the possibility of feedback) and to reduce the MTTR (Mean Time To Recovery)
  9. Mature 3rd party services to fulfil all the other needs when offering digital products. Now we can focus entirely on our business proposal (AWS/Azure & co, Observability, etc.)
  10. The readiness and willingness to learn the business we want to improve and the corresponding company culture supporting this.

This list is my Silver Bullet. All items on it are essential, and all of them exist. Most of them had a significant value for itself but the sum of them? Wow, they give us a real chance in this rapidly changing world with all its competitors running after our slice of cake.