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Raum 1708
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GP »Event-Driven Architecture in an eCommerce Application« (GP Event-Driven Architecture in ECommerce (WS23)), WS23

In this project, an eCommerce application is to be implemented using a microservice architecture. In order to achieve the highest possible resilience and decoupling, the services should communicate asynchronously with each other based on events. The goal is to explore the asynchronous pattern, overcome “mental model”, and look for good programming practices along the way.

Keywords
event-driven architecture, domain-driven design, microservice, eCommerce, software architecture
Study Program and Module Description
Master Digital Sciences (specialization Software Architecture) (see also module description in the study program web site)
Begin/End and Scheduling
Beginning of October - End of Feb 2024. Organized as an agile project with sprints every 2 weeks. Workload depends on the type of project, will be clarified at kickoff.
Location
The module takes place in a hybrid format. Please refer to the respective time slot or workshop day (see below on this page), to check if it is online or in presence. If there are no details given on this page, please check the other communication channels (e.g. Discord).
Room 1: ThoughtWorks Köln, Lichtstraße 43i, 50825 Köln (We meet at the ThoughtWorks campus in Cologne. Call me (+49 176 8072 2689) by mobile phone in case you should run late)
Room 2: Innovation Hub (Building LC7, the building to the right of the passage to Gummersbach station. The Innovation Hub is not not open to the public. However, the main entrance door is open during office hours. Come up to the second floor and ring the bell there. Please call me (+49 176 8072 2689) or a fellow student by cell phone if no one answers), see also detailed directions
Room 3: 1708 (Building LC4 (library building). Room 1708 is our lab office space, with enough room for small workshops. However, the room is only accessible with by transponder. Thereore, please be at the door left of the library entrance (where you see the label "Kriminalkommissariat", since the Gummersbach police criminal investigation unit is our office neighbour :-). I will fetch you there. Call me (+49 176 8072 2689) or a fellow student by mobile phone in case you should run late), see also detailed directions
Video conference link: https://th-koeln.zoom.us/j/4425088059?pwd=bxHOJB7D3pBHdTpruFHSdC1Y66e9Rr.1
Discord Server for fast Communication
Discord has been proven as a very effective platform for information sharing, discussions, and consultations. Therefore, please join the ArchiLab Discord Server at https://discord.gg/YYNYb5whU8. Navigate to channel #rollenzuweisung and click on gp. Then you see all channel(s) relevant for this module.

Problem Description

When making decisions within a software architecture, there is no right or wrong, there are only trade-offs. This also applies to the communication between microservices. In a previous project in the Coding Excellence (CEX) module, an attempt was made to find out what are the trade-offs between synchronous and asynchronous communication, based on events, between services using the microservice architecture of an eCommerce store.

As it turns out, it’s noticeably difficult to switch from a synchronous to an event-based architectural style. It seems that our “software education” is preparing us to think in a synchronous request / reply pattern. When switching to an asynchronous implementation, this mental model needs to be overcome, or else we’ll implement a synchronous communication pattern using asynchronous technology - and therefore will not work truly event-based. The story so far can be examined in a paper written in the module CEX.

Project Definition

An eCommerce application is to be implemented using a microservice architecture. In order to achieve the highest possible resilience and decoupling, the services should communicate asynchronously with each other based on events. Beside the event-driven service architecture, the project is focusing on

  • architectural patterns for event-based systems
  • asynchronous test concepts (Test driven design, TDD)
  • hosting / dev-ops approach (CI / CD), and
  • security aspects (https/encryption, authentication)

The goal is to explore the asynchronous pattern, overcome “mental model”, and look for good programming practices along the way. There should be even more unit tests that in a traditional test pyramid and even less integration tests. This is because in async/events, there is a larger proportion of business logic expressed as pure functions, thus unit-testable.

The “ops” part of the project is explicitly part of the implementation, trying for a true “DevOps” approach where the development team also tackles ops architecture and implementation.

Project Outcomes

The following outcomes should be delivered by the project:

  • MVP with robust, near-production-level code
  • Tests
  • A delivery pipeline able to deploy the MVP to a laboratory environment, from day one
  • Documentation with an assessment / reflection of the architectural patterns used; special attention need to be paid to the Aggregate Rules in Vaughn Vernon’s “Red Book”
  • Architecture Decision Records (ADRs) for the most important architectural decisions, esp. with hindsight to the architectural patterns used

If there is enough time, the following aspects would be an interesting extension:

  • Minimal observability capacity for microservices participating to the product
  • Minimal identity and access management for microservices participating to the product
  • Operational experimental setup able to demonstrate the resilience of the product under several service disruption scenarios
  • Operational experimental setup able to demonstrate the resilience of the product under heavy payloads

Learning Outcome

  • Understanding what a event based communication truly is
  • Knowledge about microservice architectures
  • Tradeoff for asynchronous communication between microservices with event-based message brokers
  • Testing in a asynchronous environment (e.g. unit tests, integration tests, end2end, …)
  • Knowledge in the Dev-Ops approach
  • Learning from practitioners (Michaël and Wolf from ThoughtWorks)

Requirements for participating

  • Solid coding experience in Java, .NET Core, or any other language suitable to implemented a microservice
  • Interest in architecture patterns and good practices in coding
  • Frontend or backend experience
  • Experience with an event broker (Kafka) helps, but is not a must

External Project Partner

ThoughtWorks, with Wolf Schlegel and Michaël Le Barbier both working for thoughtworks.com

Grading

The grading for this Guided Project will follow the general grading scheme for Guided Projects outlined here.

Both the quality and the effort part of the grading will be based on

  • general code quality (clean code rules, SOLID principles, clean implementation of DDD building blocks), according to a code review, and
  • the project outcomes listed above.

Workshops

Tue 17.10.2023, 09:30 - 17:00: Kickoff Workshop at ThoughtWorks

Introduction to the project, to the domain, to the technology, and to the team

Workshop Location

Room: ThoughtWorks Köln, Lichtstraße 43i, 50825 Köln (We meet at the ThoughtWorks campus in Cologne. Call me (+49 176 8072 2689) by mobile phone in case you should run late).

Goal of the day

The project is set up and ready to start.

Agenda

  • 09:30 - 10:00:  Arrival at ThoughtWorks
  • 10:00 - 10:30:  Goal of the GP and introduction to Thoughtworks (Wolf Schlegel, Stefan Bente)
    • Goal of the project
    • Introduction to ThoughtWorks (what do we do, why is this project interesting to ThoughtWorks, who of us is involved)
  • 10:30 - 11:30:  Introduction (everyone)
    • 4+1 statements methods
    • What it needs to satisfy your audience when introducing yourself – and if you want to impress them
  • 11:30 - 12:15:  Grading and Team Structure (Stefan Bente, Eberhard Schenk)
    • Grading in project part
    • Grading in Team Supervision part
    • Team structure
    • Time schedule and collaboration with DDD Master course
  • 12:15 - 13:00:  Lunch Break
  • 13:00 - 13:30:  Team identity or who are we as a team (Eberhard Schenk, Stefan Bente)
    • Team Charter concept
    • What is the agile "Definition of Done", and how are both concepts related to each other?
  • 13:30 - 14:30:  VIST Model, and possible application in Agile Retrospectives (Eberhard Schenk, Stefan Bente)
    • VIST – monitoring motivation and satisfaction of team members as a team (not as a boss)
    • There is an option instead of VIST, VIST then being a homework. This needs additional 10-15 min, prerequisite is a room with some free space to move. It is based on constellations of systemic structures in organisations; Identifying and developing the driving forces in the team and its individual team members (M. Varga von Kibed). We will decide this in the workshop.
    • What benefit has the agile retrospective, and how can it be related to the Team Supervision part of this GP?
  • 14:30 - 14:45:  Break
  • 14:45 - 15:30:  Introduction to eCommerce Domain and Technology (Wolf Schlegel)
    • We will pre-define the bounded contexts for the teams, in order to get a quicker start
    • The boundaries can be revisited later, after the joint EventStorming with the DDD course
    • Introduction to the technology stack
  • 15:30 - 16:30:  Taking DDD, Aggregates, and Domain Events seriously (Stefan Bente)
    • We will take the "red book" by Vaughn Vernon as a guiding beacon for the project, when it comes to implementation of aggregates, and modelling of domain events
    • Introduction to the "aggregate rules" by Vaughn Vernon; see dedicated info page
    • What are domain events, and how do they relate to aggregates?
    • Discussion
  • 16:30 - 17:00:  Next Steps (all)

Mon 27.11.2023, 10:00 - 17:00: EventStorming Workshop

Organized by the DDD Master course, this workshop will bring together all teams of the GP and the DDD course, to collaboratively model the domain of the eCommerce application. We will use the EventStorming technique for this.

Workshop Location

Room: Innovation Hub (Building LC7, the building to the right of the passage to Gummersbach station. The Innovation Hub is not not open to the public. However, the main entrance door is open during office hours. Come up to the second floor and ring the bell there. Please call me (+49 176 8072 2689) or a fellow student by cell phone if no one answers), see also detailed directions.

Goal of the day

Domain events have been identified, and possibly inconsistencies in the bounded contexts boundaries.

Tue 28.11.2023, 10:00 - 17:00: Hackathon

The day will be used for coding and discussing architectural issues.

Workshop Location

Room: Innovation Hub (Building LC7, the building to the right of the passage to Gummersbach station. The Innovation Hub is not not open to the public. However, the main entrance door is open during office hours. Come up to the second floor and ring the bell there. Please call me (+49 176 8072 2689) or a fellow student by cell phone if no one answers), see also detailed directions.

Goal of the day

Ready to tackle the next sprints.

Wed 03.01.2024, 10:00 - 17:00: Hackathon

The day will be used for coding and discussing architectural issues.

Workshop Location

Room: Innovation Hub (Building LC7, the building to the right of the passage to Gummersbach station. The Innovation Hub is not not open to the public. However, the main entrance door is open during office hours. Come up to the second floor and ring the bell there. Please call me (+49 176 8072 2689) or a fellow student by cell phone if no one answers), see also detailed directions.

Thu 04.01.2024, 10:00 - 17:00: Hackathon

The day will be used for coding and discussing architectural issues.

Workshop Location

Room: Innovation Hub (Building LC7, the building to the right of the passage to Gummersbach station. The Innovation Hub is not not open to the public. However, the main entrance door is open during office hours. Come up to the second floor and ring the bell there. Please call me (+49 176 8072 2689) or a fellow student by cell phone if no one answers), see also detailed directions.

Fri 05.01.2024, 10:00 - 17:00: Hackathon

The day will be used for coding and discussing architectural issues.

Workshop Location

Room: Innovation Hub (Building LC7, the building to the right of the passage to Gummersbach station. The Innovation Hub is not not open to the public. However, the main entrance door is open during office hours. Come up to the second floor and ring the bell there. Please call me (+49 176 8072 2689) or a fellow student by cell phone if no one answers), see also detailed directions.