NATS

NATS provides lightweight, high-performance messaging with simple operations and cloud-native design.

Why NATS

Strength	Benefit
Lightweight	Single binary, minimal resources
Fast	Sub-millisecond latency
Simple	Minimal configuration
Cloud native	Built for Kubernetes
JetStream	Persistent streaming option

Trade-offs

Concern	Consideration
Less mature	Smaller ecosystem than Kafka/RabbitMQ
Durability	Requires JetStream for persistence

Configuration

[bus]
backend = "nats"

[bus.nats]
url = "nats://localhost:4222"
# For JetStream (persistent)
jetstream = true
stream_name = "angzarr-events"

Environment Variables

export NATS_URL="nats://localhost:4222"
export BUS_BACKEND="nats"

Subject Layout

NATS uses dot-separated subjects for hierarchical routing:

angzarr.events.player.PlayerRegistered
angzarr.events.player.FundsDeposited
angzarr.events.hand.CardsDealt

Subscriptions

Wildcards enable flexible subscriptions:

angzarr.events.player.*    # All player events
angzarr.events.*.>         # All events
angzarr.events.hand.>      # All hand events and sub-subjects

Core NATS vs JetStream

Core NATS (Fire and Forget)

Pub/sub without persistence
At-most-once delivery
Lowest latency
Use for ephemeral events

JetStream (Persistent)

Stream persistence
At-least-once delivery
Consumer replay
Use for event sourcing

# Enable JetStream for event sourcing
[bus.nats]
jetstream = true

JetStream Configuration

# Create stream
nats stream add angzarr-events \
  --subjects "angzarr.events.>" \
  --retention limits \
  --max-msgs -1 \
  --max-bytes -1 \
  --max-age 7d \
  --storage file \
  --replicas 3

# Create consumer
nats consumer add angzarr-events player-projector \
  --filter "angzarr.events.player.>" \
  --ack explicit \
  --deliver all \
  --max-deliver 5 \
  --replay instant

Docker Setup

# Core NATS
docker run -p 4222:4222 nats:latest

# NATS with JetStream
docker run -p 4222:4222 nats:latest -js

Helm Deployment

bus:
  backend: nats

nats:
  enabled: true
  url: nats://nats.messaging.svc.cluster.local:4222
  jetstream: true
  streamName: angzarr-events

Monitoring

NATS provides a monitoring endpoint:

http://localhost:8222/varz    # Server stats
http://localhost:8222/connz   # Connections
http://localhost:8222/subsz   # Subscriptions
http://localhost:8222/jsz     # JetStream stats

When to Use NATS

Edge computing — Minimal resource footprint
Kubernetes native — Designed for containers
Simple operations — Single binary, little config
High performance — Sub-millisecond latency

Next Steps

AMQP — More features, larger ecosystem
Kafka — Higher throughput alternative