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Architecture & Design Follow 903 Followers

Event Sourcing in an Unreliable World

by Jan Stenberg Follow 10 Followers on  Nov 30, 2017

Examples of event sourced systems are often from process-oriented domains, like e-commerce, with incoming commands that generate events. But there are domains without processes that are intrinsically unreliable where we are collecting events from external event sources with transports that are unreliable, Lorenzo Nicora explained at the recent Microservices Conference µCon London 2017.

Architecture & Design Follow 903 Followers

Designing Event Sourced Microservices

by Jan Stenberg Follow 10 Followers on  Nov 12, 2017

Event sourced microservices is an area that hasn’t been explored nearly as much as it should be, Greg Young claimed at the recent Microservices Conference µCon London 2017, but he also strongly emphasized that you should not event source all your microservices. Instead, he recommends looking at individual services and applying the event sourcing pattern to services that actually benefit from it.

Architecture & Design Follow 903 Followers

Event Architectures and Event Streaming

by Jan Stenberg Follow 10 Followers on  Sep 06, 2017

When moving from a monolithic system to a distributed or microservices system, you commonly also move from a single source of truth in one database to many databases and thus many sources of truth. Using an event architecture and persisting all events as a stream can give back the single source of truth, Ben Stopford claims in one of a series of blog posts about events, event streams and Kafka.

Architecture & Design Follow 903 Followers

Selecting an Event Architecture

by Jan Stenberg Follow 10 Followers on  Aug 24, 2017

When designing a distributed system, maybe based on microservices, and you are considering an event architecture, there are several models and technologies available. When choosing how to implement the architecture the non-functional requirements are a main factor, David Dawson claims when describing different styles of event architectures in a recent blog post.

Architecture & Design Follow 903 Followers

QCon New York 2017: Scaling Event Sourcing for Netflix Downloads

by Andrew Morgan Follow 0 Followers on  Aug 23, 2017

Phillipa Avery, senior software engineer at Netflix, and Robert Reta, senior software engineer at Netflix, presented their Cassandra-backed event sourcing architecture at QCon New York 2017. Currently, it powers the download feature in Netflix, and was summarised as something which improved the flexibility, reliability, scalability and debuggability of their services.

Architecture & Design Follow 903 Followers

Versioning of Events in Event Sourced Systems

by Jan Stenberg Follow 10 Followers on  Jul 17, 2017

A challenge with event sourced systems is that events put in the event store years ago must be readable today, even though the software has gone through numerous changes, Greg Young stated in his presentation at this year’s DDD eXchange conference. If a system can be taken down, versioning of events is relatively simple. The real challenge comes when a system can’t be taken down.

Architecture & Design Follow 903 Followers

Moving a Monolithic Application towards a Microservices Architecture

by Jan Stenberg Follow 10 Followers on  Dec 31, 2016

Migrating an existing system towards microservices is very different from building a new micoservices-based system, Joris Kuipers, architect at Trfork Amsterdam, claims in a presentation describing an ongoing process of refactoring a large monolithic application, based on CQRS using Axon framework, towards a microservices architecture.

Architecture & Design Follow 903 Followers

Start with Events and DDD When Building Microservices

by Jan Stenberg Follow 10 Followers on  Dec 28, 2016 2

Domain-Driven Design (DDD) is a great technique bringing designs closer to the domains we are working in, but too often we make early decisions with a focus on structure, which is not the intention of DDD. Instead we should start with the events in a domain, Russ Miles claims when describing the advantages of going “events-first” when building microservices.

Architecture & Design Follow 903 Followers

Vaughn Vernon on Microservices and Domain-Driven Design

by Jan Stenberg Follow 10 Followers on  Jul 31, 2016

Although a monolith can be modeled in a respectable way, often they are turned into a big ball of mud. This is caused by multiple domain models becoming entangled within the monolith, and in Vaughn Vernon's experience this can happen within a few weeks or months, he claimed in a presentation at the Scala Days conference earlier this year.

Architecture & Design Follow 903 Followers

Eric Evans: Is Domain-Driven Design Beneficial for Software Development?

by Jan Stenberg Follow 10 Followers on  Jun 16, 2016 1

The last couple of years the interest in Domain-Driven Design (DDD) has increased, Eric Evans noted in his keynote at the recent DDD eXchange conference in London. He thinks that we are in a time when developers care more about design, partially because we are working more with distributed systems where models have a higher value.

Architecture & Design Follow 903 Followers

Comparison of Event Sourcing with Stream Processing

by Jan Stenberg Follow 10 Followers on  May 25, 2016

Event sourcing and CQRS are two patterns that has emerged in the Domain-Driven Design (DDD) community. Stream processing builds on similar ideas but has emerged in a different community, Martin Kleppmann noted in his presentation at the Domain-Driven Design Europe conference earlier this year comparing event sourcing with stream processing.

Architecture & Design Follow 903 Followers

A Whole System Based on Event Sourcing is an Anti-Pattern

by Jan Stenberg Follow 10 Followers on  Apr 26, 2016 5

Command Query Responsibility Segregation (CQRS) was never meant to be the end goal of what we are trying to achieve, it is a stepping stone towards the ideas of Event sourcing, Greg Young stated in his presentation at the Domain-Driven Design Europe conference earlier this year. He noted though that just applying CQRS is still a valuable pattern.

Architecture & Design Follow 903 Followers

Lagom, a New Microservices Framework

by Jan Stenberg Follow 10 Followers on  Mar 08, 2016 1

Lightbend, the company behind Akka, has released an open source microservices framework, Lagom built on their Reactive Platform, in particular the Play Framework and the Akka family of products together with ConductR for deployment. By default, Lagom is message-driven and asynchronous, and using distributed CQRS persistence patterns with event sourcing as the primary implementation.

Architecture & Design Follow 903 Followers

CQRS Example Using Axon Framework

by Jan Stenberg Follow 10 Followers on  Jan 31, 2016

Command Query Responsibility Segregation (CQRS) separates the part that changes the state from the part that queries the state in an application. Axon is a Java framework implementing the building blocks of CQRS to help in when building CQRS applications, Dadepo Aderemi, writes in a series of blog post explaining CQRS by building a small demo application based on the Axon Framework.

Architecture & Design Follow 903 Followers

CQRS, Read Models and Persistence

by Jan Stenberg Follow 10 Followers on  Oct 20, 2015 4

Storing events in a relational database and creating the event identity as a globally unique and sequentially increasing number is an important and maybe uncommon decision when working with an event-sourced Command Query Responsibility Segregation (CQRS) system Konrad Garus writes in three blog posts describing his experiences from a recent project building a system of relatively low scale.

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