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Building an A2A Message Broker

The Nervous System for AI Agent Fleets

Build the connective tissue that lets AI agents talk to each other — deterministic routing, org-based authority, audit-before-dispatch, and the SDK pattern. Drawn from a real production broker running 24/7.

Recommended: Complete Multi-Agent Orchestration first

8 lessons~75 min total

Lessons are shown in recommended order. Complete them in sequence for the best experience — or jump to any lesson.

Lesson 189·9 min read

Why Agents Need a Nervous System

37 repos communicating via cron and Discord is not architecture — it is chaos with good intentions, and it breaks the moment the fleet grows.

Lesson 190·10 min read

Deterministic Routing — No LLM in the Router

Nine routing rules cover every message type in the fleet — evaluated in order, first match wins, zero LLM calls, no exceptions.

Lesson 191·9 min read

Agent Cards as Identity

Every agent in the fleet has an Agent Card — a structured JSON document that encodes identity, org position, capabilities, and authority ceilings, loaded at broker startup and used in every routing decision.

Lesson 192·11 min read

The Message Pipeline

Nine steps from NATS receive to Akashic store — each step has a specific job, and skipping any of them breaks a different guarantee.

Lesson 193·9 min read

NATS as Internal Transport

NATS was chosen for the Invictus Labs fleet because it handles pub/sub fan-out natively, runs as a single binary with no broker to manage, and crosses the local network to Tesseract without configuration.

Lesson 194·9 min read

Audit Before Dispatch

Write to the immutable SQLite audit log before sending the message — an undelivered message that was logged is recoverable, but an unlogged message that was delivered is invisible forever.

Lesson 195·8 min read

SSE for Real-Time Cockpit

Server-Sent Events give Mission Control a live window into every message the broker routes — broadcast_event pushes to all subscribers with queue overflow protection and 30-second keepalives.

Lesson 196·10 min read

The SDK Pattern

BrokerClient gives every agent a consistent interface to the broker — fire-and-forget publish, automatic heartbeat, and a local SQLite buffer that drains on reconnect when NATS goes down.