IOS 11: Fixing APN Configuration Issues

So a few days ago I’ve decided to move to another cellular carrier. I pushed the new sim-card in, and got greeted with “Could not activate cellular data network”. First instinct was to install the new carrier’s APN configuration profile, but this resulted in another bummer: “Only one APN configuration can be installed at a time”. Ok, so I have to delete the previous carrier’s profile. Settings -> General -> Profiles …and there weren’t any profiles: “No profiles are currently installed”. [Read More]

Tackling Complexity in Microservices

Tackling Complexity in Microservices

Microservices have taken our industry by storm. Teams around the world have ditched their clumsy monoliths in favor of chasing the dream of loosely coupled, manageable, and independently deployable microservices. Unfortunately, many of them ended up worse off than they were before - in the realm of distributed monoliths. Why?

“If I had an hour to solve a problem I’d spend 55 minutes thinking about the problem and 5 minutes thinking about solutions” - Albert Einstein

In my opinion, this quote is the key to solving most of the issues we have when designing microservices-based systems. We rush into solutions without ensuring we know what exactly a microservice is. In this post, I’d like to take a stab at answering this question.

[Read More]

Revisiting the Basics of Domain-Driven Design

Revisiting the Basics of Domain-Driven Design

I have quite a few friends in the DDD community. Fortunately, or not, we always tend to disagree on the definitions of such basic terms as Domains and Subdomains. In this post, I want to think aloud and outline my thoughts on the subject.

Disclaimer

As I just said, some of the things I’m about to write are my opinion only. Many of you might disagree with some of them. Hey – the last time we spoke about it, Eric and Vaughn were not fans of my theory. But, nevertheless, it is based on my 7-year long DDD journey at our company, and it works for me. I believe it might work for you as well.

[Read More]

Bounded Contexts are NOT Microservices

Rebel scum

I’ve always considered Domain-Driven Design’s Bounded Context as a guideline for defining the boundaries of Microservices. I was wrong. Not only is this heuristic flawed, but Bounded Contexts are the exact opposite of Microservices! To explain this point of view, I’ll start with a quick refresh of what Bounded Contexts are; then I’ll discuss the relationship between Bounded Contexts and Microservices.

[Read More]

Apache NiFi: Enabling Unicode Support

If you’re using Apache NiFi to move data around, you might stumble upon Unicode characters turning into question marks. For example, the ExecuteSQL processor does that. To fix this you have to set JVM’s default encoding to UTF-8.

[Read More]

Tackling Complexity in CQRS

Tackling Complexity in CQRS

The CQRS pattern can do wonders: it can maximize scalability, performance, security, and even “beat” the CAP theorem. Nonetheless, CQRS has acquired a controversial name because of the complexity it introduces. For instance, in his article on CQRS, Martin Fowler argues that the pattern should be applied sparingly and even cautiously:

  • “… for most systems CQRS adds risky complexity”
  • “… you should be very cautious about using CQRS”
  • “So while CQRS is a pattern that’s good to have in the toolbox, beware that it is difficult to use well and you can easily chop off important bits if you mishandle it.”

From my point of view, the CQRS-induced complexity is largely accidental, and thus can be avoided. To illustrate my point, I want to discuss the goal of CQRS, and then analyze 3 common sources of accidental complexity in CQRS-based systems.

[Read More]

Finding Proper Scopes for Unit Tests

In my previous rant post on TDD I’ve argued that the majority of the problems many experience doing TDD are caused by testing in too narrow scopes - using classes as units of testability, instead of functional use cases. However, widening the scope of the test too much is just another extreme. So how one finds the sweet spot? In this post I’d like to share the heuristic that I use.

[Read More]

Tackling Complexity in the Heart of DDD

Tackling Complexity in the Heart of Domain-Driven Design

Let’s do a little experiment: try to explain the gist of Domain-Driven Design to someone who has no clue about it. This, especially doing it succinctly, is not easy. Heck, I struggle with it myself. Bounded contexts, entities, domain events, value objects, domains, aggregates, repositories… where do you even start?

To find the order in the apparent chaos, I want to analyze the DDD methodology from a rather unusual perspective — by applying Domain-Driven Design to Domain-Driven Design itself. After all, this methodology is intended to deal with complex domains, isn’t it?

[Read More]

A Quick and Dirty Hack for Interviewing Job Candidates

A Quick and Dirty Hack for Interviewing Job Candidates

One simple question can shed a lot of light on one’s competency in a given field: “On a scale of 1 to 10, please rate your knowledge of [enter-name-of-the-field-here]“.

One can assume that the higher the grade, the better. But that’s not the case at all. Why? Science — that’s why. Enter the Dunning-Kruger effect.

[Read More]

DDDEU 2016 Impressions

Last month, I had the pleasure of attending the Domain Driven Design Europe conference in Brussels. As I’ve tweeted before, this was the best conference I’ve ever attended. In this post, I’d like to sum the things I’ve learned at the conference.

It’s Not (Only) About Sessions

It was the first time I’ve attended a conference alone. Honestly, I was afraid that my introverted side would take over, and I’d master wallflower imitation techniques between sessions. Fortunately, it didn’t happen. I felt at home the moment I left the hotel for the conference. From that moment on, and up until the very last moments of the conference, I met a lot of like-minded people from all over the world - Belgium, Denmark, Germany, Austria, UK, Poland, Italy, France, USA, Finland, Switzerland, Netherlands, Romania, Bulgaria, and even from Israel.

For me, the social part, alone, was worth the trip. And don’t get me wrong, the sessions were great, but the ability to meet new friends, share experiences and ideas, and get fresh perspectives, was priceless. And I’m yet to mention discussing Star Wars with Eric Evans, discovering that Vaughn Vernon knows Israel better than I do, catching up with Greg Young, and last but not least, drinking beer with Yves Reynhout — it is unbelievable how much I learned from Yves that evening.

Lesson learned: Go to conferences alone and meet new people.

[Read More]