Apache EventMesh is a new generation serverless event middleware for building distributed event-driven applications.
EventMesh adopts a unified CloudEvents-over-MQ architecture. The message queue (MQ) acts as a pure write-ahead log (WAL) for durable storage only — there are no consumer groups, no tags, and no broker-side subscription semantics. Instead, the stateless EventMesh Runtime owns all delivery logic: its SubscriptionManager maintains the subscription registry and offset tracking, and dispatches events with load-balance, broadcast, and multicast semantics. Applications interact through a lightweight HTTP + CloudEvents 1.0 SDK (publish / subscribe / unsubscribe), while integration with external systems runs in a standalone Connector Runtime via the connector SPI.
Apache EventMesh is packed with features that help users build event-driven applications with ease. Here are the highlights that set EventMesh apart:
Core architecture
- CloudEvents-native, end to end — built entirely around the CloudEvents 1.0 specification, so events stay vendor-neutral and portable.
- Lightweight, language-agnostic SDK — just three operations over plain HTTP (
publish,subscribe,unsubscribe); no heavyweight client, no vendor lock-in. - Runtime-owned subscription & dispatch — subscription state and delivery semantics (load-balance / broadcast / multicast) are managed by EventMesh itself, not the underlying MQ, giving you consistent behavior across any storage backend.
- MQ as a pure write-ahead log (WAL) — append-only, no consumer groups, no tags; the broker is reduced to durable storage, dramatically simplifying operations.
- Guaranteed at-least-once delivery — EventMesh owns reliability through self-managed offsets and explicit ACK.
- Multiple delivery transports — subscribers choose HTTP long-polling, Server-Sent Events (SSE), or WebSocket push, with request-reply support.
- Effortless horizontal scaling — stateless Runtime instances scale out seamlessly with no rebalancing cost.
Extensibility & ecosystem
- Agent-to-Agent (A2A) collaboration — a built-in A2A protocol turns EventMesh into an agent collaboration bus, bridging synchronous MCP / JSON-RPC 2.0 tool calls and asynchronous event-driven pub/sub for LLM and multi-agent systems.
- Pluggable storage layer — Apache RocketMQ, Apache Kafka, Apache Pulsar, RabbitMQ, Redis, and more.
- Pluggable interconnector layer — connectors run as standalone processes acting as the source or sink of SaaS, CloudService, Database, etc.
- Pluggable meta service — Consul, Nacos, ETCD, and Zookeeper.
- Event schema management via catalog service.
- Powerful event orchestration through the Serverless workflow engine.
- Powerful event filtering and transformation.
Each EventMesh surface carries an explicit maturity status. The table below is the single source of truth — module-level docs link here instead of restating their status. See docs for the per-capability guides.
| Capability | Status | Recommendation | Migration target |
|---|---|---|---|
| HTTP + CloudEvents | GA target | Recommended — the primary user path (CloudEventsClient + /events/*) |
Primary path |
| Kafka / RocketMQ storage (4.x, 5.x) | GA target | Recommended — pluggable WAL backends, TCK-covered (MeshStoragePluginTCK) |
Primary path |
| SSE / WebSocket push | Beta | Usable — integration-tested; unified ACK/redelivery semantics still landing | Unified push transports |
| Connector Runtime | Beta | Usable — 24 connector plugins on the standalone runtime | New connector SPI migration |
| A2A / Agent Gateway | Experimental | Evaluate — task store + runtime bridge landed (#5302/#5304); reaper & Meta-backed agent cards pending | Unified Runtime A2A |
| TCP / gRPC / OpenMessaging SDKs | Legacy-compatible | Existing users only — kept so old clients run unmodified; not extended | HTTP + CloudEvents |
Status meanings:
- GA target — feature-complete for the current architecture, integration-tested against real brokers; safe for production.
- Beta — functional and tested, but semantics or deployment shape may still shift in a minor release.
- Experimental — under active development; APIs and storage layouts may break; wire it up on dev clusters first.
- Legacy-compatible — maintained for zero-change compatibility with existing clients; receives fixes but no new features. New integrations should not start here.
Migrating off TCP / gRPC SDKs? The legacy clients keep working against the current runtime; see the client guide for the HTTP + CloudEvents replacement (
CloudEventsClient).
- Getting started — zero to running runtime in minutes
- Configuration reference — every runtime key, per-backend settings, security & quota
- Client guide — complete
CloudEventsClientwalkthrough (pub/sub, request-reply, streaming, lite topics) - Architecture — control / data / agent planes; storage SPI; security gate; A2A stack
- Features — feature-by-feature guide (pub/sub, A2A, connectors, security, reliability)
- EventMesh-site: Apache official website resources for EventMesh.
- EventMesh-workflow: Serverless workflow runtime for event Orchestration on EventMesh.
- EventMesh-dashboard: Operation and maintenance console of EventMesh.
- EventMesh-catalog: Catalog service for event schema management using AsyncAPI.
- EventMesh-go: A go implementation for EventMesh runtime.
A full step-by-step walkthrough — prerequisites, backend choice, run via Docker
or from source, first publish, three receive transports, unsubscribe, and the SDK
path — lives in Getting started. The
first-event examples in that guide work against the standard ports
(8080 HTTP, 8081 admin, 8082 WebSocket, 8083 connector admin).
Each contributor has played an important role in promoting the robust development of Apache EventMesh. We sincerely appreciate all contributors who have contributed code and documents.
Apache EventMesh enriches the CNCF Cloud Native Landscape.
Apache EventMesh is licensed under the Apache License, Version 2.0.
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