Build a multi-agent system: A2A & Agent Registry // TRAIN BRAIN

Build a multi-agent system: A2A & Agent Registry

Github repo → https://goo.gle/multiagent
When you have 100 AI agents across your org, how do they find and talk to each other? This is how: the Agent2Agent (A2A) Protocol and Agent Registry. In this episode of Hands On AI, we build a production-ready multi-agent system. We start with the Agent2Agent (A2A) Protocol, think "HTTP for AI agents", then solve agent sprawl with Agent Registry, so your agents discover each other instead of hard-coding URLs.
We build it live with a dog walker agent and a trip planner agent on Google's Agent Development Kit (ADK), then orchestrate them together.
What you'll learn:
* What the A2A protocol is, and when to use it for multi-agent systems.
* Agent cards — an agent's "LinkedIn profile" for discovery.
* Sync vs async agent communication (polling vs streaming).
* Wrapping an ADK agent as an A2A remote agent with to_a2a.
* The agent sprawl problem — and how Agent Registry solves it (reusability, one way to connect, governance).
* Registering agents via gcloud and the Cloud console.
* Using Agent Registry's MCP server to discover agents + tools dynamically — no more hard-coded URLs.
* Bringing in third-party agents (LangGraph, CrewAI) and MCP servers.
Chapters:
00:00 - Intro: Agent2Agent (A2A) Protocol & Agent Registry
03:06 - What Is Agent2Agent (A2A) Protocol? (HTTP for AI agents)
04:29 - When & why to use A2A
06:31 - Agent cards: An agent's LinkedIn profile
09:34 - Sync vs async communication
11:20 - Demo: building a dog walker agent (ADK)
15:21 - Wrapping an agent as an A2A remote agent
17:20 - Connecting two agents with A2A
19:27 - The problem: Agent sprawl
20:05 - What is Agent Registry?
22:35 - Registering agents (gcloud + console)
27:13 - Beyond agents: MCP servers & endpoints
29:18 - Connecting through the registry — No more hard-coded URLs
35:36 - Demo: The orchestrator agent
41:09 - Authentication & wrap up
More resources:
Google Agent Development Kit (ADK) → https://goo.gle/3PItVzL
Agent Runtime → https://goo.gle/4nXDhnX
Agent Registry / Agent Platform → https://goo.gle/4aZAdlM
Agent2Agent Protocol (A2A) protocol → https://goo.gle/4u5x8HF
Sita Lakshmi on LinkedIn → https://goo.gle/3QyQzLl
Annie Wang on LinkedIn → https://goo.gle/43GCXAo
Watch more Hands on AI → https://www.youtube.com/playlist?list=PLIivdWyY5sqKnJOvP89yF8t9mWuzMTcbM
? Subscribe to Google Cloud Tech → https://goo.gle/GoogleCloudTech
Speakers: Sita Lakshmi, Annie Wang
Products Mentioned: Google Agent Development Kit, Gemini API, Agent Runtime, AgentRegistry, Agent2Agent (A2A) Protocol

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