How do you handle event versioning in microservices using event sourcing?

Event sourcing is a design pattern where state changes in a system are stored as a sequence of events. In the context of microservices, event sourcing provides a way to achieve consistency across distributed systems by ensuring that all changes to application state are stored as a sequence of immutable events. However, a challenge arises when you need to handle event versioning, which is essential for maintaining the integrity of your system as it evolves. You must carefully manage changes to the event structure to avoid disrupting the services that rely on these events.

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1 Event Sourcing

Event sourcing involves capturing all changes to an application's state as a sequence of events. In a microservices architecture, these events are immutable and provide a reliable audit trail that can be used to reconstruct the application state at any point in time. This approach is particularly useful for complex systems where you need to ensure complete traceability and accountability for state changes. By storing events rather than just the current state, you enable more sophisticated data analysis and debugging capabilities, which is a critical aspect of Business Intelligence (BI).

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Prashant Thomas ☁

Azure Solutions Architect Expert | Administrator Associate | DBA | Data Scientist | UiPath Solution Architect | TOGAF 9.2 | CSM
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At Verbanet Technologies, we adopted event sourcing for our microservices architecture to manage a complex e-commerce platform. Initially, we faced challenges with versioning events. Each service published events that were consumed by others, but changes in event schemas caused frequent integration issues. To address this, we implemented versioning by including a version number in the event metadata. Services were designed to handle multiple versions, ensuring backward compatibility. This approach allowed us to evolve our event schemas without disrupting the system. The result was a more resilient architecture, with improved traceability and easier debugging, significantly enhancing our Business Intelligence capabilities.

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2 Versioning Strategy

When applying event sourcing in microservices, you'll need a robust versioning strategy to handle changes in the structure of events. One common approach is to use semantic versioning for events, which involves incrementing major versions for breaking changes and minor versions for non-breaking changes. This allows consumers of the events to understand the nature of the changes and adapt accordingly. It's important to maintain backward compatibility where possible, so that existing consumers do not break when a new version is introduced.

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Prashant Thomas ☁

Azure Solutions Architect Expert | Administrator Associate | DBA | Data Scientist | UiPath Solution Architect | TOGAF 9.2 | CSM
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At Verbanet Technologies, we tackled event versioning in our microservices by adopting a dual-schema approach. When an event schema needed changes, we published both the old and new versions of the event simultaneously. Each event carried a schema version identifier, allowing consumers to choose which version to process. This approach ensured backward compatibility and gave teams the flexibility to migrate to the new schema at their own pace. By maintaining both versions until all consumers had migrated, we avoided breaking changes and ensured a smooth transition. This method significantly reduced downtime and integration issues, enhancing overall system stability.

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3 Upcasting Events

Upcasting is a technique used to transform older versions of events to the current version without altering the original event data. This is done in-memory when the event is read from the event store. Upcasting allows you to evolve your event schema while ensuring that older events remain readable and relevant. It's a crucial process for maintaining data integrity and ensuring that all microservices can continue to function correctly, even as the system evolves.

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Prashant Thomas ☁

Azure Solutions Architect Expert | Administrator Associate | DBA | Data Scientist | UiPath Solution Architect | TOGAF 9.2 | CSM
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At Verbanet Technologies, we used upcasting to handle event versioning in our financial microservices system. When we needed to add new fields to transaction events, we didn't alter the existing stored events. Instead, we implemented upcasters that transformed older event versions to the latest schema in-memory during read operations. This allowed us to introduce new features without disrupting existing services. By keeping the original event data intact, we maintained data integrity and ensured that all services, regardless of their update status, could process events seamlessly. This approach minimized downtime and kept our system robust and adaptable.

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4 Transformation Layer

Implementing a transformation layer can help manage different event versions effectively. This layer sits between the event store and the services that consume events, and it's responsible for converting events to the version expected by the consuming service. This decouples the event schema from service logic, allowing services to operate independently without being affected by changes in event structure. The transformation layer can handle upcasting and other necessary conversions, providing a flexible buffer that helps maintain system robustness.

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5 Consumer Adaptation

Consumer services must be designed to handle different versions of events gracefully. This can be achieved by implementing logic within the services to adapt to non-breaking changes in events. For breaking changes, services may need to support multiple versions concurrently or use an anti-corruption layer to interact with the event store. It's essential for maintaining service availability and ensuring that the system can evolve without causing disruptions to ongoing operations.

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6 Event Store Design

The design of the event store plays a pivotal role in handling event versioning. It should support storing events in a format that includes version metadata, and it should be capable of evolving alongside your microservices architecture. An event store that is designed with versioning in mind will facilitate easier migrations to new versions and provide better support for concurrent versions, which is vital for a resilient microservices ecosystem.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How do you handle event versioning in microservices using event sourcing?

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1 Event Sourcing

2 Versioning Strategy

3 Upcasting Events

4 Transformation Layer

5 Consumer Adaptation

6 Event Store Design

7 Here’s what else to consider

Business Intelligence

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How do you handle event versioning in microservices using event sourcing?

1

2

3

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5

6

7

1 Event Sourcing

2 Versioning Strategy

3 Upcasting Events

4 Transformation Layer

5 Consumer Adaptation

6 Event Store Design

7 Here’s what else to consider

Business Intelligence

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