[CNCF LFX Proposal] Apicurio Registry: CloudEvents Webhook Notifications for Schema Changes

### CNCF Project

Apicurio Registry

### Term

2026 Term 3 (Sep-Nov)

### Program Name

CloudEvents Webhook Notifications for Schema Changes

### Program Description

## Description
In event-driven architectures, a schema change in the registry can break every producer and consumer downstream. Today, the only way to detect changes in Apicurio Registry is to poll the API. A breaking schema change could cascade through a Kafka pipeline before anyone notices.

This project adds a webhook notification system that emits CloudEvents (CNCF Graduated) when registry state changes. The mentee will design the event schema, implement the subscription API, build the delivery engine with at-least-once semantics and retry logic, and store everything in the SQL database. The result is a production-ready notification system for the SQL storage variant.

## Expected outcomes
- CloudEvents-compliant event schema for artifact created, version published, rule violated, artifact deprecated
- Webhook subscription REST API (register endpoints, choose event types, filter by group/artifact type)
- Delivery engine with at-least-once semantics and exponential backoff retry
- SQL schema migration for subscriptions and delivery logs
- Integration tests covering subscribe → trigger → verify delivery → verify retry

### Technologies

Java, Quarkus, PostgreSQL, CloudEvents, REST, Testcontainers

### Skills same as Technologies?

- [x] Yes, the required skills are the same as the technologies listed above.

### Required/Desirable Skills

_No response_

### Mentors

Carles Arnal | @carlesarnal | carnalca@ibm.com | carnalca
Paolo Antinori | @paoloantinori | pantinor@ibm.com | pantinor

### Upstream Issue URL

https://github.com/Apicurio/apicurio-registry/issues/8426

### Application Prerequisites

- [x] Resume
- [x] Cover Letter
- [ ] School Enrollment Verification
- [ ] Participation Permission from school or employer
- [ ] Coding Challenge
- [ ] Custom Prerequisite (fill in details below)

### Coding Challenge URL

_No response_

### Custom Prerequisite Name

_No response_

### Custom Prerequisite Description

_No response_

### Custom Prerequisite — File Upload

- [ ] Yes — completion of this task requires the mentee to submit a file.

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**LFX program:** [CNCF - Apicurio Registry: CloudEvents Webhook Notifications for Schema Changes (2026 Term 3)](https://mentorship.lfx.linuxfoundation.org/project/f85f019e-f28a-4116-a87f-fe77608b7ac9)

Start with the linked upstream issue, Apicurio Registry #8426, and review the proposal's expected outcomes. Identify the existing REST, SQL storage, and integration-test entry points before designing the subscription API and delivery flow. Done means CloudEvents notifications, subscription persistence, retries, migrations, and subscribe-to-delivery integration tests are implemented for the SQL variant.

Written by the indexing model from the issue text.