“We can solve any problem by introducing an extra level of indirection” — Event Sourcing is the privileged model to do it.

The idea of Event Sourcing is the following: to capture and save the changes of an application state as events. Before the term has been coined by Martin Fowler, the idea was referred as the Append-Only-Log, Write-Ahead-Log or simply the Log.

Capturing and saving all the application changes has the advantage of allowing to know the state of the application for any given instant and also to know how it got there. Event Sourcing brings two key features…

Debt is a good analogy to explain what happens with code if no care is taken:

Debt grows if not payed.
It can lead to chronic abuse.
Cumulative debt grows exponentially.
Eventually leads to bankruptcy.

However It can be useful if tactically used. Can be a leverage if well managed. Debt has the implicit urgency of payment. It’s a useful concept to communicate with stakeholders. There is some emotional triggering when someone finds he is in debt. However, there are different types of debt. Not all debt is created equal.

The first category we can assign to code debt is…

I’ve seen many implementations of Event Sourcing that use a message broker to publish events to the read models. I’ve used that pattern and contributed to ES “frameworks” that implement that pattern. I think It is a bad idea. I’ll explain why:

1) Writing to the event store AND publishing events to a broker needs to be atomic. In most cases a distributed transaction using two phase commits is not an option. We need to create some mechanism to deal with faulty connections between publisher and broker:

Part I: Intro

Microservices are an architectural pattern that allows big software systems to be break in smaller parts. Each microservice can be developed, maintained, deployed and operated independently.

Microservices share the same general principles of any modular architecture: break the system into smaller, independent, loosely coupled modules that communicate using a well defined interface (API).

As a student I never liked language subjects. Portuguese, English, French. But now I regret not have taken more advantage of it. Specially the French. Portuguese is my main language and English is so global that you would learn it anyway. But French and others escaped.

Although I regret not have learned more languages sooner, I believe the blame is not entirely on me, neither on all the students that struggle with the education system. In fact I believe there is something very wrong about how education currently works.

I believe we all are beings of emotion and expression need…

In the summer of 2005, the president George W. Bush, after reading a book about the 1918 pandemic, created an action plan prepared for a pandemic scenario. The plan included funding for vaccine research, storage of essential supplies and a playbook and simulation exercises. It seems that he realised the importance of speed of action in a pandemic scenario:

“A pandemic is a lot like a forest fire,” Bush said at the time. “If caught early it might be extinguished with limited damage. …

The year of 2019 ended, it’s time to get a retrospective about the year readings. I read less than I would like but nevertheless it was a year of wonderful discoveries. Any type of review is tricky. Unless you are an expert on the subject matter, any review says much more about the author of the review than about the subject. What I’m writing here are just a couple of paragraphs about what the books did for me, not trying to put myself on the shoes of any book critics.

You can check my Goodreads profile here.

1984 — George Orwell

The communism experience…

• You can read the part 1 here.
• You can read the part 2 here.

In the last parts it was presented an evolutionary path towards an event driven architecture to support multiple read models. We ended with an architecture with a relational database that supports write operations where the business invariants are ensured, an event queue, a broker to dispatch messages, and an Integrator to update changes to read-only databases (Image 1). In this part 3 It will be presented an Event Sourcing alternative and be discussed some nuances in the adoption of such solution.

Image 1 — Final Architecture…