NATS & JetStream | Zander's Code Notes

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What is NATS? Jump to heading

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 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 Jump to heading

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

CLI Help Jump to heading

nats -h
nats cheat
nats cheat sub
nats cheat pub

Core Messaging CLI Jump to heading

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 Jump to heading

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 Jump to heading

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 Jump to heading

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 Jump to heading

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 Jump to heading

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 Jump to heading

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`) Jump to heading

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

Context Management Jump to heading

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 Jump to heading

# 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 Jump to heading

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

Publish Messages Jump to heading

# 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

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