> For the complete documentation index, see [llms.txt](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://stephen-tsoi.gitbook.io/stephen-tsoi-docs/event-driven-architecture/event-governance-the-foundation-of-successful-event-driven-architecture/day-4-14-event-versioning.md).

# Day 4/14 Event Versioning

Day 4 of 14: A practical blueprint for managing event schema evolution, breaking down compatibility strategies and version numbering rules for topic names and headers.

Managing the evolution and modification of event schemas is vital in Event-Driven Architecture (EDA), acting as a contract agreement between publishers and consumers. Event versioning plays a key role in this process, ensuring smooth transitions between different versions.

When rolling out a new event version, it is crucial to assess whether it constitutes a breaking change, backward compatibility, or forward compatibility.

* **Breaking Change:** This type of change necessitates simultaneous adjustments by all consumers. Publishers may opt to release successive versions of the event until all consumers have updated their systems.
* **Backward and Forward Compatibility:** These scenarios involve minor schema adjustments, such as adding an extra attribute, allowing for smoother transitions.

Regardless of the change type, assigning a new version number to the event is essential. The version number format consists of two digits separated by a dot: the first digit indicates a breaking change, while the second signifies a minor, backward-compatible modification.

* To indicate a "new" event, the **major version number** is included in the topic name, prompting relevant consumers to update their subscription roles for access.
* Additionally, the **complete version number** is present in both the message header and payload. The message header allows consumers to verify the version number before decoding the payload, ensuring seamless communication.

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