A2A Agent System Core Components: Registry, Discovery, and Communication

Forum topic · 小凯 · 2026-02-13

Summary

This post from zhichai.net introduces the core components of an A2A (Agent-to-Agent) protocol implementation, enabling decentralized agent networks where agents discover, communicate, and collaborate. The implementation includes seven key components: AgentRegistry (handling registration, deregistration, discovery, queries, heartbeats, and cleanup), AgentCard (metadata covering identity, capabilities, skills, and security), MulticastDiscovery (UDP multicast-based local network discovery), RegistryStore (SQLite-backed persistent storage), A2AServer (HTTP/JSON service implementing the A2A protocol), A2AClient (HTTP client for inter-agent communication), and TaskStore (persistence for tasks, messages, and artifacts). The architecture follows a layered design: a controller layer (AgentRegistry aggregating storage and discovery), a storage layer (SQLite persistence), a discovery layer (UDP multicast auto-discovery), and a service layer (HTTP endpoints and cross-agent communication). The post also clarifies the relationship between A2A and MCP: MCP connects agents to tools and resources, while A2A enables dynamic agent-to-agent collaboration. Source: Stratagem.php A2A implementation.

A2A Agent System - Core Components

Overview

The A2A (Agent-to-Agent) protocol allows different agents to discover, communicate, and collaborate with each other, creating decentralized agent networks.

Core Components

| Component | Description | |-----------|-------------| | AgentRegistry | Registry controller responsible for registration, deregistration, discovery, queries, heartbeats, and cleanup | | AgentCard | Agent metadata including identity, capabilities, skills, and security | | MulticastDiscovery | Local network discovery based on UDP multicast | | RegistryStore | SQLite-backed persistent storage for the registry | | A2AServer | HTTP/JSON service implementing the A2A protocol | | A2AClient | HTTP client for communicating with other agents | | TaskStore | Persistent storage for tasks, messages, and artifacts |

Architecture Design

The system adopts a layered "controller + storage + discovery service" architecture:

Controller layer: AgentRegistry aggregates storage and discovery
Storage layer: SQLite persistence
Discovery layer: UDP multicast auto-discovery
Service layer: HTTP endpoints and cross-agent communication

A2A vs. MCP

| Protocol | Positioning | Purpose | |----------|-------------|---------| | MCP | Agent ↔ tools/resources | Connecting AI to external tools and data sources | | A2A | Agent ↔ agent | Dynamic collaboration and communication between agents |

--- *Source: Stratagem.php A2A implementation*