Event-Driven Architecture (EDA) is exciting until you deal with event versioning.

There is one way: Send meeting invites to all teams. After 101 meetings, post your maintenance banner, and everyone hits the release button at the same time. Or...

Or you can use an Adapter but with a twist. Yes, like in 90% of the problems in Software Development, there is a Pattern that will help you find a smart solution.

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The Problem

At this point, you understand the domain better, and a structural change makes perfect sense.

The problem is that you have a schema, and consumers already know how to process it, so they depend on you to keep compatibility but really need to break it.

Let’s talk about an example with a producer and 3 consumers.

Components Diagram - Visualized using Multiplayer

The solution

Instead of falling into the trap of coordinated deployments, you can leverage the Adapter Pattern with a strategic twist. Here’s how it works in 5 steps:

Initial Setup - Sketched using Multiplayer

Create a New Topic: When you introduce a new schema, instead of forcing all consumers to immediately adapt, you create a new topic. This topic will be the home for events generated using the new schema.

Introduce an Adapter: Deploy an adapter that listens to the new topic. This adapter translates the events back to the old schema format and republishes them to the original topic. This way, your existing consumers continue receiving events in the format they expect without any immediate changes.

Update the Producer: Modify the producer to generate events using the new schema and publish these events to the newly created topic.

Preparing the road for migration - Sketched using Multiplayer

Gradually Migrate Consumers: Now that you have both the old and new formats coexisting, you can start migrating consumers at your own pace. As you update each consumer to handle the new schema, simply point it to the new topic.

Two consumers migrated, and one more to go - Sketched using Multiplayer

Decommission the Adapter: Once all consumers have been successfully migrated to the new schema, you can safely retire the adapter and the old topic.

Migration completed - Sketched using Multiplayer

The Benefits: Less Stress, More Agility

Backward Compatibility: The adapter ensures that your existing consumers continue to function without requiring immediate updates, maintaining system stability during the transition.

No Coordinated Deployments: By decoupling the migration of the producer and consumers, you eliminate the need for synchronized deployments. Each team can work independently, reducing the risk of errors.

Focused Testing: As each consumer is migrated, testing can be more focused and controlled. You can validate each transition individually, making identifying and resolving issues easier.

Reduced Meetings: With less coordination required, you can say goodbye to countless meetings. The migration process becomes simpler, more predictable, and less stressful.

The goal is to find the simplest and most effective solutions to breaking compatibility.

The Adapter Pattern provides a pragmatic approach to handling event versioning in EDA.

Say no to more meetings and start releasing the smart way: incrementally!

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