Year: 2017

DDD, Hexagonal, Onion, Clean, CQRS, … How I put it all together

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned about Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

After graduating from University I followed a career as a high school teacher until a few years ago I decided to drop it and become a full-time software developer.

From then on, I have always felt like I need to recover the “lost” time and learn as much as possible, as fast as possible. So I have become a bit of an addict in experimenting, reading and writing, with a special focus on software design and architecture. That’s why I write these posts, to help me learn.

In my last posts, I’ve been writing about many of the concepts and principles that I’ve learned and a bit about how I reason about them. But I see these as just pieces of big a puzzle.

Today’s post is about how I fit all of these pieces together and, as it seems I should give it a name, I call it Explicit Architecture. Furthermore, these concepts have all “passed their battle trials” and are used in production code on highly demanding platforms. One is a SaaS e-com platform with thousands of web-shops worldwide, another one is a marketplace, live in 2 countries with a message bus that handles over 20 million messages per month.

Continue reading “DDD, Hexagonal, Onion, Clean, CQRS, … How I put it all together” →

Service Oriented Architecture (SOA)

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

The SOA Style has been around since the late 1980s and has its origins in ideas introduced by CORBA, DCOM, DCE and others. Much has been said about SOA, and there are a few different implementation patterns but, in essence, SOA focuses on only a few concepts and doesn’t give any prescription on how to implement them:

  • Composability of user-facing applications;
  • Reusable Business Services;
  • Technology stack independent;
  • Autonomy (independent evolution, scalability & deployability).

SOA is a set of architectural principles independent of any technology or product, just like polymorphism and encapsulation are.

In this post I am going to address the following patterns related to SOA:

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From CQS to CQRS

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

When we have an application that is data-centric, ie. implements only basic CRUD operations and leaves the business process (ie. what data to change and in what order) to the user, we have the advantage that the users can change the business process without the need to change the application. In the other hand, this implies that all users need to know all details of all business processes that can be performed using the application, which is a big problem when we have non-trivial processes and a lot of people that need to know them.

In a data-centric application, the application has no knowledge of the business processes, so the domain is unable to have any verbs, and is unable to do anything else aside from changing raw data. It becomes a glorified abstraction of the data model. The processes exist only in the heads of the application users, or even in post-its pinned to the computer screen.

A non-trivial, and really useful, application aims to remove the “process” burden from the user’s shoulders by capturing their intentions, making it an application capable of processing behaviours as opposed to simply storing data.

CQRS is the result of an evolution of several technical concepts that work together to help provide the application with an accurate reflection of the domain, while overcoming common technical limitations. Continue reading “From CQS to CQRS” →

Event-Driven Architecture

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

Using events to design applications is a practice that seems to be around since the late 1980s. We can use events anywhere in the frontend or backend. When a button is pressed, when some data changes or some backend action is performed.

But what is it exactly? When should we use it and how? What are the downsides?

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Clean Architecture: Standing on the shoulders of giants

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

Robert C. Martin (AKA Uncle Bob) published his ideas about Clean Architecture back in 2012, in a post on his blog, and lectured about it at a few conferences.

The Clean Architecture leverages well-known and not so well-known concepts, rules, and patterns, explaining how to fit them together, to propose a standardised way of building applications.

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Onion Architecture

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

The Onion Architecture was coined by Jeffrey Palermo in 2008. As I see it, it builds on the Ports & Adapters Architecture by adhering to the idea of placing the domain in the centre of the application, externalising the delivery mechanisms (UI) and infrastructure used by the system (ORM, Search engines, 3rd party APIs, …). But it goes further and adds internal layers to it.

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Ports & Adapters Architecture

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

The Ports & Adapters Architecture (aka Hexagonal Architecture) was thought of by Alistair Cockburn and written down on his blog in 2005. This is how he defines its goal in one sentence:

Allow an application to equally be driven by users, programs, automated test or batch scripts, and to be developed and tested in isolation from its eventual run-time devices and databases.

Alistair Cockburn 2005, Ports and Adapters

I’ve seen some articles talking about the Ports & Adapters Architecture that said a lot about layers. However, I haven’t read anything about layers in the original Alistair Cockburn post.

The idea is to think about our application as the central artefact of a system, where all input and output reaches/leaves the application through a port that isolates the application from external tools, technologies and delivery mechanisms. The application should have no knowledge of who/what is sending input or receiving its output. This is intended to provide some protection against the evolution of technology and business requirements, which can make products obsolete shortly after they are developed, because of technology/vendor lock-down.

In this post, I’m going to dive into the following subjects:

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Domain-Driven Design

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

Domain-Driven Design was coined by Eric Evans in his fantastic book Domain-Driven Design: Tackling Complexity in the Heart of Software, published in 2003. Eric Evans book was key in formalising many of the software development concepts that today we take for granted.

I can’t make an exhaustive review of DDD in a blog post. There are just too many important concepts associated with DDD. Fortunately, that’s also not the goal here. What I will do, however, is to list the DDD concepts that I find more relevant for the way I like to organise code and how I think of Architecture: the system-wide concepts that constitute the foundations for feature development.

In this post, I’m going to write about:

  • Ubiquitous language
  • Layers
  • Bounded contexts
  • Anti-Corruption Layer
  • Shared Kernel
  • Generic Subdomain

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Packaging & namespacing

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

The architecture of a system is the high-level view of that system, the big picture, the system design in broad strokes. The architectural decisions are the structural decisions in the system, the ones that affect the whole code base, the ones that define where everything else will be built on top of.

Amongst other things, architecture is responsible for deciding the systems:

  • Components
  • Relationships between components
  • Principles guiding the design and evolution of components and relationships

In other words, these are the design decisions that are more difficult to change as the system evolves, it’s the foundations that give support to feature development.

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EBI Architecture

This post is part of The Software Architecture Chronicles, a series of posts about Software Architecture. In them, I write about what I’ve learned on Software Architecture, how I think of it, and how I use that knowledge. The contents of this post might make more sense if you read the previous posts in this series.

The Entity-Boundary-Interactor (EBI) Architecture has been made known by Robert C. Martin in his talks about Clean Architecture (of which I will talk in a later post).

However, this pattern was published by Ivar Jacobson back in 1992, in his book Object-Oriented Software Engineering: A use case driven approach. At the time, Jacobson actually called it Entity-Interface-Control, but the name was changed so that “Interface” would not be confused with the “Interface” language construct (which some languages don’t even have) nor with “User Interface”, and “Control” would not be confused with the MVC Controller.

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