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Apache EventMesh

Apache EventMesh is a new generation serverless event middleware for building distributed event-driven applications.

EventMesh Architecture

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.

Features

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.
• LLM streaming agent runtime — a standalone agent process hosts OpenAI-compatible LLM streaming sessions on the mesh, with function-calling tools: any connector becomes an agent tool, custom tools ship as agent plugins (SPI), and topics can drive agents as event triggers with decisions published back for sink delivery.
• Pluggable storage layer — Apache RocketMQ (4.x / 5.x) and Apache Kafka ship today, plus a zero-dependency in-memory backend as the dev/CI default; more backends via the MeshStoragePlugin SPI.
• Pluggable interconnector layer — connectors run as standalone processes acting as the source or sink of SaaS, CloudService, Database, etc.
• Pluggable meta service — Nacos ships today (multi-instance coordination); more backends via the same storage SPI.
• Event schema management via catalog service.
• Powerful event orchestration through the Serverless workflow engine.
• Powerful event filtering and transformation.

Capability status

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.

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). The legacy gRPC SDK surface is served again since the #5411 bridge (opt-in via eventmesh.grpc.port=10205) — old EventMeshGrpcProducer / EventMeshGrpcConsumer clients run unmodified on the v2 runtime.

Documentation

The docs tree is organized by audience — start from the documentation map:

• Introduction — what EventMesh is and when to use it
• Getting started — zero to a running runtime in minutes
• Configuration reference — every runtime key, per-backend settings, security & quota
• User guides — Java client · pub/sub · delivery reliability · streaming · lite topic · A2A · agent tools
• Architecture — overview · control plane · security
• API & operations — HTTP API · admin API · observability · deployment · protocols & SDKs · storage SPI

Subprojects

• 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.

Quick start

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 (10105 HTTP, 10106 admin, 10107 WebSocket opt-in).

Contributing

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.

• Contributing Guideline
• Good First Issues

CNCF Landscape

Apache EventMesh enriches the CNCF Cloud Native Landscape.

License

Apache EventMesh is licensed under the Apache License, Version 2.0.

Community

Bi-weekly meeting : #Tencent meeting : 346-6926-0133

Bi-weekly meeting record : bilibili

Mailing List