AWS User Group UK Meetup #79

Welcome to our September event. We’re delighted to welcome [Yan Cui](https://www.linkedin.com/in/theburningmonk/), AWS Serverless Hero, independent consultant and [Martin Thwaites](https://www.linkedin.com/in/martindotnet/), Principal Developer Advocate, Honeycomb.io

Here’s what they’re bringing:

Event-driven architecture solves your coupling problem and hands you three new ones. Yan has run production workloads on AWS since 2009 and has trained thousands of developers on EventBridge and Lambda, so he knows exactly where the neat whiteboard diagram falls apart: tracing a request with no call stack, changing an event without breaking consumers you don’t control, and failures that land minutes after the original request. Tonight Yan is giving us the patterns that hold up in production - event envelopes that give you versioning, idempotency and tracing for free, end-to-end tests that stay inside your own bounded context, and a hard look at where governance earns its overhead.

65,000 attendees. Four days. A booth game that has to survive the moment a keynote ends. Martin built Battleships for the Honeycomb booth on EKS, then rebuilt it on Lambda MicroVMs the month they launched, giving every player their own machine with no shared state and no pod to fight over. Tonight Martin is walking us through the rebuild: the cost modelling against EKS, what changed once a session owned a whole VM, and the instrumentation that tells him the game is degrading before an attendee does.

A big thank you to our sponsors [Cloudscaler](https://rebrand.ly/cloudscaler) & [Rayo](https://rebrand.ly/rayo-cloud).

Programme: 18:00: Arrival, registration 18:15: Talks start 20:00: Networking with food and a drink provided by the generosity of our sponsors.

Session 1: *Event-driven architecture: the hard parts* *with Yan Cui* Event-driven architectures are great at helping teams build loosely coupled, scalable systems - but the neat architecture diagrams rarely show the difficult bits. In practice, they hand you a fresh set of problems that nobody warns you about at the whiteboard stage.

Once events start flowing across multiple services and bounded contexts, new challenges emerge. How do you trace a request end-to-end when there’s no longer a simple call stack? How do you change an event without unexpectedly breaking consumers you don’t control? And how do you test and operate a system where failures can happen asynchronously, perhaps minutes after the original request? In this talk, Yan will explore the practical lessons and patterns that make event-driven architectures work in production, including:

• End-to-end observability as events flow across services and asynchronous boundaries • Testing strategies within bounded contexts, and deciding what should, and shouldn’t, be tested end-to-end • Schema evolution and how to change events safely without breaking existing consumers • Catching integration problems early, before they reach production • Error handling, retries and idempotency, including dealing with duplicate and out-of-order events • Documentation and governance so teams can understand which events exist, who owns them and how they should be used

Drawing on real-world experience building event-driven systems on AWS, Yan will look beyond the happy path and focus on the trade-offs, failure modes and engineering practices that help these architectures remain manageable as systems and teams grow.

Learning Takeaways

• How to design an event envelope that gives you versioning, idempotency and tracing for free • Why “no breaking changes” often beats every event versioning scheme, and how to enforce it • A practical way to scope end-to-end tests so they don’t spill into other teams’ systems • Where governance is worth the operational overhead, and where it just slows you down

Yan is an AWS Serverless Hero and independent consultant who has run production workloads on AWS since 2009. He helps teams go faster for less with serverless, and has…