NATS & JetStream

What is NATS?

NATS is a lightweight, high-performance messaging system for cloud-native applications, microservices, and IoT, utilizing a publish-subscribe model for efficient communication.

Key functions include:

• Data Synchronization: Keeps data synchronized across network actors
• Message Handling: Publishes and subscribes to lightweight messages
• Multi-tenancy Support: Isolates clients for enhanced security and flexibility
• Integration: Connects with systems like Snowflake for low-latency data analytics

Core NATS

Core NATS operates on a publish-subscribe model using subject/topic-based addressing. This offers two significant advantages: location independence and a default many-to-many (M:N) communication pattern. These enable powerful solutions for common development patterns like microservices, without requiring load balancers, API gateways, or DNS configuration.

Core NATS provides at-most-once (best-effort) message delivery. JetStream adds persistence with at-least-once and exactly-once semantics.

Concept	Description
Subjects	Hierarchical, dot-separated strings (e.g., orders.us.new)
* wildcard	Matches a single token
> wildcard	Matches all remaining tokens
Pub/Sub	One-to-many fan-out messaging
Request/Reply	One-to-one with built-in reply subject

CLI Installation

brew tap nats-io/nats-tools
brew install nats-io/nats-tools/nats

CLI Help

nats -h
nats cheat
nats cheat sub
nats cheat pub

Core Messaging CLI

Command	Description
nats pub <subject> <message>	Publish a message to a subject
nats sub <subject>	Subscribe and listen for messages
nats request <subject> <data>	Send request and wait for reply
nats reply <subject> <data>	Listen for requests and send replies
nats bench <subject>	Run a performance benchmark

JetStream

JetStream is the built-in persistence engine providing at-least-once or exactly-once delivery.

Concept	Description
Streams	Message stores capturing data published to specific subjects
Consumers	Stateful views tracking delivered/acknowledged messages
Pull Consumer	Client requests batches of messages (recommended for scalability)
Push Consumer	Server delivers messages to a specified subject

Stream Management

Command	Description
nats account info	Check JetStream status and account limits
nats stream add <name>	Create a new stream (interactive)
nats stream ls	List all streams
nats stream info <name>	View stream config and state
nats stream view <name>	Browse messages in a stream
nats stream rm <name>	Delete a stream
nats stream purge <name>	Purge all messages from a stream
nats stream edit <name>	Edit stream configuration

Consumer Management

Command	Description
nats consumer add <stream>	Create a consumer (interactive)
nats consumer ls <stream>	List consumers for a stream
nats consumer info <stream> <consumer>	View consumer state
nats consumer next <stream> <consumer>	Fetch next message (pull consumer)
nats consumer rm <stream> <consumer>	Delete a consumer

Key-Value Store

Command	Description
nats kv add <bucket>	Create a KV bucket
nats kv put <bucket> <key> <value>	Set a key
nats kv get <bucket> <key>	Get a key
nats kv del <bucket> <key>	Delete a key
nats kv ls <bucket>	List keys in a bucket
nats kv rm <bucket>	Delete a bucket
nats kv watch <bucket>	Watch for changes

Object Store

Command	Description
nats obj add <bucket>	Create an object store bucket
nats obj put <bucket> <file>	Upload a file
nats obj get <bucket> <name>	Download a file
nats obj ls <bucket>	List objects
nats obj rm <bucket>	Delete a bucket

Server

Command	Description
nats-server	Start NATS server
nats-server -js	Start with JetStream enabled
nats-server -m 8222	Enable HTTP monitoring on port 8222
nats server info	View connected server info
nats server ping	Ping all servers in cluster

Config Example (server.conf)

jetstream {
  store_dir: "/data/nats-jetstream"
  max_mem: 1G
  max_file: 10G
}

Context Management

Contexts save common connection config (server, credentials) for reuse.

Command	Description
nats context save <name> --server <url> --creds <file>	Create a context
nats context select <name>	Switch to a context
nats context ls	List available contexts
nats context rm <name>	Remove a context

Example: Create and Use a Context

# Save a context with server and credentials
nats context save mycontext --server nats.example.com --creds ~/my.creds

# Subscribe using a context
nats sub --context mycontext "prices.>"

# Publish using a context
nats pub --context mycontext "prices.USD" "1.25"

Examples

Subscribe to a Subject

nats --server nats.example.com sub "prices.>"
nats --server 10.20.125.100 sub 'test.subject'

Publish Messages

# Simple message
nats pub subject_name "Hello World"

# JSON payload
nats pub subject_name '{"key": "value", "number": 42}'

# Publish from file
cat data.json | nats pub subject_name