We all know the joke about distributed systems right? There are only two hard problems in distributed systems: 2. Exactly-once delivery 1. Guaranteed order of messages 2. Exactly-once delivery — Mathias Verraes (@mathiasverraes) August 14, 2015 (btw you should go follow Mathias if you don’t already) 1 Exactly-once delivery defined First of all: Exactly-once delivery guarantee is the guarantee that a message can be delivered to a recipient once, and only once.

This is the second blog post in a short series about Consistency I love the two generals problem. I am mesmerized by its simplicity and impossibility. And I believe nothing has shaped my professional life more than this problem. Back in 2008 I had not yet worked with any major distributed systems, and most of my work was with systems which involved heavy aspects of custom electronics; one could say I was into IoT before IoT was a thing.

This is the first blog in a short series about Consistency When I decided to start my blog again, I created a poll about what should I write first. The reason was that I have gathered material about 2-3 subjects which I liked and wanted to speak about, but I wasn’t sure which one to start with. More people voted than I expected, but the decision was a tie between what different types of events would be helpful to recognise in an Event Sourced system, and Distributed consistency.

The problems I have been having quite a lot of very interesting discussions lately on multiple subjects, and I kept facing the below problems repeatedly: I needed to explain the same things again, sometimes with some minor details changed The medium through which the discussion was being had didn’t help in expanding adequately Sometimes people interposed in the middle of an argument, or the discussion would change subject slightly while I felt there were things not adequately covered After some thinking about it, I decided to start blogging again (what happened to the old blog is a story for another time btw), and start writing in a way that will help me address the above problems.

Hello and welcome to my blog. My name is Savvas Kleanthous. Hello to everyone who knows me 👋 I was born in southern part of Cyprus, but I’ve been living in London for the past 6-7 years now. I am the Head of Engineering for ParcelVision and we are creating a set of services for large retailers and logistic-related companies. I have been working with DDD, CQRS and Event sourcing for quite a while now, as I find that paradigm to be particularly interesting to me, and I also enjoy the challenges which usually merit such an approach.