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NATS CLI Messaging and JetStream

Version 0.5.0 · source

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Start here

nats context add <name> --server <url> --select
Save a server
nats sub <subject>
Listen to a subject
nats pub <subject> "<msg>"
Publish a message
nats request <subject> "<msg>"
Ask and wait for a reply
nats stream add <name> --subjects "<subject>.>"
Persist messages
nats stream ls
List streams
nats consumer next <stream> <consumer>
Pull stored messages
nats kv put <bucket> <key> <value>
Store a value

Concepts

  1. Publisher nats pub
  2. Server routes by subject
  3. Stream JetStream, stored
  4. Consumer cursor + acks

Connect and contexts

nats context add <name> --server <url> --select
Save a server as a context
Credentials, TLS and other connection flags can be stored in the context too.
nats context ls
List saved contexts
nats context select <name>
Switch context
nats --server <url> <command>
Use a server without a context
Short form -s. Also read from NATS_URL.
nats --creds <file> <command>
Authenticate with a .creds file
NATS_URL=<url> nats <command>
Set the server by environment

Publish and subscribe

nats pub <subject> "<msg>"
Publish a message
nats sub <subject>
Print messages as they arrive
nats sub "<prefix>.>"
Subscribe to a whole subject tree
nats sub <subject> --queue <group>
Share messages across a queue group
echo "<msg>" | nats pub <subject>
Publish from stdin
nats pub <subject> "<msg>" --jetstream
Publish and wait for a stream ack
Short form -J.

Request and reply

nats request <subject> "<msg>"
Send a request, print the reply
nats reply "<subject>" "<body>"
Answer requests with a fixed body
nats reply "<subject>" --command "<cmd>"
Answer with a command's output
{{N}} in the command is replaced by the Nth subject token.

Server and account

nats account info
Show account limits and usage
nats-server -js
Start a local server with JetStream

Streams

nats stream add <name> --subjects "<s>.>" --defaults
Create a stream
--defaults skips the prompts. A subject can belong to only one stream.
nats stream ls
List streams
nats stream info <name>
Show config and state
nats stream view <name>
Browse stored messages
Needs an interactive terminal.
nats stream rm <name>
Delete a stream
-f skips the confirmation.
nats stream purge <name>
Remove all messages
--keep <n> or --subject <subject> narrows it.

Consumers

nats consumer add <stream> <consumer> --pull --defaults
Create a durable pull consumer
The consumer name is positional; there is no --durable flag.
nats consumer next <stream> <consumer> --count <n>
Fetch and ack n messages
nats consumer ls <stream>
List a stream's consumers
nats consumer info <stream> <consumer>
Show pending and ack state

Key-Value store

nats kv add <bucket>
Create a bucket
--history <n> keeps up to 64 revisions per key (default 1).
nats kv put <bucket> <key> <value>
Set a key
Key names reject some characters such as a colon; use - _ . / instead.
nats kv get <bucket> <key>
Read a key
Add --raw to print only the value.
nats kv ls
List buckets
nats kv watch <bucket>
Stream changes live
Add a key to watch just that one.
nats kv ls <bucket>
List keys in a bucket
nats kv del <bucket> <key>
Delete a key (leaves a marker)
Without a key it deletes the whole bucket.
nats kv history <bucket> <key>
Show all revisions of a key

Object store

nats object get <bucket> <name>
Download a file
--output <path> picks the target path.
nats object put <bucket> <file>
Upload a file

Benchmark

nats bench pub <subject> --msgs <n> --clients <n>
Measure publish throughput
Add --no-progress for clean output.

Recipes

Local JetStream playground
nats-server -js &nats context add local --server nats://127.0.0.1:4222 --selectnats stream add ORDERS --subjects "orders.>" --defaultsnats pub orders.new "order 1"
Work through a pull consumer
nats consumer add ORDERS shipping --pull --defaultsnats consumer next ORDERS shipping --count 5
Watch a config key
nats kv add CONFIG --history 5nats kv watch CONFIG &nats kv put CONFIG feature.x on