Messaging (Flash)

Status: Active | Port: 4222, 8222 | Profile: think, reason, ultra-instinct

The arc-messaging service (Flash) is the platform message broker built on NATS. It carries low-latency, ephemeral messages between platform services and agent workers — the fast synchronous layer of the A.R.C. messaging system.

For durable event streaming with persistence and replay, see Streaming (Dr. Strange).

Quick Reference

Field	Value
Image	ghcr.io/arc-framework/arc-messaging:latest
Port(s)	4222 (client), 8222 (monitoring)
Health	http://localhost:8222/healthz
Profile(s)	think, reason, ultra-instinct (core)

Make Targets

Target	Description
make messaging-up	Start the service
make messaging-down	Stop the service
make messaging-health	Check health
make messaging-logs	Tail service logs

When to Use Messaging (Flash)

Messaging (Flash) is ideal for synchronous, ephemeral communication:

Use Case	Messaging (Flash)	Streaming (Dr. Strange)
Agent asks another agent to act	✅	❌
Distribute work across workers	✅ (queue groups)	❌
Request/reply pattern	✅	❌
Heartbeat / presence	✅	❌
Event sourcing / audit log	❌	✅
Replay historical events	❌	✅
Cross-service event distribution	❌	✅

Rule of thumb: If you need the other side to respond now, use arc-messaging. If you need a durable record that can be replayed later, use arc-streaming.

Features

• Sub-millisecond latency — in-memory only, no disk I/O
• Pub/sub — fan-out to multiple subscribers
• Request/reply — synchronous RPC over messaging
• Queue groups — load-balanced work distribution
• Lightweight — minimal CPU and RAM footprint

Connection

# Default client URL
nats://localhost:4222

# Monitoring dashboard
open http://localhost:8222

Patterns

Pub/Sub (Fan-out)

Publisher → Topic → Subscriber A
                  → Subscriber B
                  → Subscriber C

Request/Reply (RPC)

Agent A → request(topic, payload) → Agent B
Agent A ←    reply(result)        ←

Queue Group (Load Balancing)

Job Queue → Worker 1
          → Worker 2 (only one receives each message)
          → Worker 3

Reasoner Integration

The Reasoner service (Sherlock) uses arc-messaging (Flash) as its primary async trigger. See Reasoner for the full NATS subject schema used by the platform.