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

Forum topic · 小凯 · 2026-02-13

Summary

This post outlines the core components of an A2A (Agent-to-Agent) protocol implementation, which enables AI agents to discover, communicate, and collaborate across a decentralized agent network. Key components include AgentRegistry (a controller handling registration, deregistration, discovery, queries, heartbeats, and cleanup), AgentCard (metadata for agent identity, capabilities, skills, and security), MulticastDiscovery (UDP-based local network discovery), RegistryStore (SQLite-backed persistence), A2AServer and A2AClient (HTTP/JSON protocol endpoints and clients), and TaskStore (persistence for tasks, messages, and artifacts). The architecture follows a layered design: controller layer (AgentRegistry aggregating storage and discovery), storage layer (SQLite), discovery layer (UDP multicast auto-discovery), and service layer (HTTP endpoints and inter-agent communication). The post also clarifies the relationship between A2A and MCP: MCP connects an agent to tools and resources, while A2A handles dynamic agent-to-agent collaboration and communication.

A2A Agent System — Core Components

Overview

The A2A (Agent-to-Agent) protocol allows different agents to discover, communicate with, and collaborate with each other, creating a decentralized network of intelligent agents.

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 | UDP multicast-based local network discovery implementation | | RegistryStore | SQLite-based persistent registry storage | | 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 automatic discovery
Service layer: HTTP endpoints and cross-agent communication

A2A vs MCP

| Protocol | Positioning | Use Case | |----------|-------------|----------| | 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*