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Karan Pratap Singh
Karan Pratap Singh

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Introduction to NATS CLI

#tutorial #distributedsystems

In this article, we’ll take a look at NATS CLI and learn some basics commands. In my opinion NATS CLI is quite underrated, it offers many features and can help eliminate most of the manual scripts used to manage a NATS server.

Installation

For OS X brew can be used to install the latest version:

$ brew tap nats-io/nats-tools
$ brew install nats-io/nats-tools/nats
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For more installation options, check Github releases

Features

  • JetStream management
  • JetStream data and configuration backup
  • Message publish and subscribe
  • Service requests and creation
  • Benchmarking and Latency testing
  • Super Cluster observation
  • Configuration context maintenance
  • NATS ecosystem schema registry

Commands

Let’s learn about some basic commands. But first, let’s start our nats-server locally with JetStream so that we can try out the commands.

Note: To enable JetStream we can use the -js or --jetstream flag.

$ nats-server -js
[48351] 2022/04/04 17:01:50.947435 [INF] Starting nats-server
[48351] 2022/04/04 17:01:50.947518 [INF]   Version:  2.7.4
[48351] 2022/04/04 17:01:50.947521 [INF]   Git:      [not set]
[48351] 2022/04/04 17:01:50.947524 [INF]   Name:     NDYZJMTC6C6D2DJHVJEPWOF5SE4BZVKE5WFDJOUBFYE6JMP5EUDL27SZ
[48351] 2022/04/04 17:01:50.947529 [INF]   Node:     MiRXijo7
[48351] 2022/04/04 17:01:50.947532 [INF]   ID:       NDYZJMTC6C6D2DJHVJEPWOF5SE4BZVKE5WFDJOUBFYE6JMP5EUDL27SZ
[48351] 2022/04/04 17:01:50.947792 [INF] Starting JetStream
[48351] 2022/04/04 17:01:50.948188 [INF]     _ ___ _____ ___ _____ ___ ___   _   __  __
[48351] 2022/04/04 17:01:50.948202 [INF]  _ | | __|_   _/ __|_   _| _ \ __| /_\ |  \/  |
[48351] 2022/04/04 17:01:50.948204 [INF] | || | _|  | | \__ \ | | |   / _| / _ \| |\/| |
[48351] 2022/04/04 17:01:50.948206 [INF]  \__/|___| |_| |___/ |_| |_|_\___/_/ \_\_|  |_|
[48351] 2022/04/04 17:01:50.948207 [INF]
[48351] 2022/04/04 17:01:50.948209 [INF]          https://docs.nats.io/jetstream
[48351] 2022/04/04 17:01:50.948211 [INF]
[48351] 2022/04/04 17:01:50.948213 [INF] ---------------- JETSTREAM ----------------
[48351] 2022/04/04 17:01:50.948217 [INF]   Max Memory:      12.00 GB
[48351] 2022/04/04 17:01:50.948221 [INF]   Max Storage:     275.69 GB
[48351] 2022/04/04 17:01:50.948223 [INF]   Store Directory: "/var/folders/zj/t9pthq5n5s109_02bq2gf13w0000gn/T/nats/jetstream"
[48351] 2022/04/04 17:01:50.948225 [INF] -------------------------------------------
[48351] 2022/04/04 17:01:50.948639 [INF] Listening for client connections on 0.0.0.0:4222
[48351] 2022/04/04 17:01:50.948849 [INF] Server is ready
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Context

The nats CLI supports multiple named configurations. We refer to these configurations as “context”. In these contexts, we can configure the server, credentials, certs, and much more.

Usage

To manage nats configuration contexts, we use the context command.

usage: nats context <command> [<args> ...]
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Save

To create or update a context we can use the context save sub-command.

$ nats context save my-context --server=demo.nats.io
NATS Configuration Context "my-context"

      Server URLs: demo.nats.io
             Path: /..../.config/nats/context/my-context.json
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Note: we can also use the --user and --password flags to add credentials to the context.

Select

Now that have created our context, we can select it using the context select sub-command.

$ nats context select my-context
NATS Configuration Context "my-context"

      Server URLs: demo.nats.io
             Path: /..../.config/nats/context/my-context.json
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List

And now if we list known contexts using the context ls sub-command, we can see our my-context being selected.

$ nats context ls
╭───────────────────────────╮
│      Known Contexts       │
├─────────────┬─────────────┤
│ Name        │ Description │
├─────────────┼─────────────┤
│ my-context* │             │
╰─────────────┴─────────────╯
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Removing

We can also easily remove the context using the context rm sub-command.

$ nats context rm my-context
? Really delete context "my-context" Yes
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Account

Info

We can use info command to view account information and connection

$ nats account info
Connection Information:

               Client ID: 4
               Client IP: 127.0.0.1
                     RTT: 77.542µs
       Headers Supported: true
         Maximum Payload: 1.0 MiB
           Connected URL: nats://127.0.0.1:4222
       Connected Address: 127.0.0.1:4222
     Connected Server ID: ND5TMCZ32LWFSFQGTMMADGCERCQE4C6A2P6DAVPK76WFE4LAM56AZ26N

JetStream Account Information:

Configuration Requirements:

   Requires Max Bytes Set: false

Stream Resource Usage Limits:

      Memory: 0 B of Unlimited
     Storage: 0 B of Unlimited
     Streams: 0 of Unlimited
   Consumers: 0 of Unlimited
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connections

report connections as the name suggest report connection for our command

$ nats account report connections

╭──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│                                                                          Top 1 Connections out of 1 by subs                                                                          │
├─────┬─────────────────────────┬──────────────────────────────────────────────────────────┬─────────┬───────────┬─────────┬────────┬─────────┬──────────┬──────────┬───────────┬──────┤
│ CID │ Name                    │ Server                                                   │ Cluster │ IP        │ Account │ Uptime │ In Msgs │ Out Msgs │ In Bytes │ Out Bytes │ Subs │
├─────┼─────────────────────────┼──────────────────────────────────────────────────────────┼─────────┼───────────┼─────────┼────────┼─────────┼──────────┼──────────┼───────────┼──────┤
│ 5   │ NATS CLI Version 0.0.30 │ ND5TMCZ32LWFSFQGTMMADGCERCQE4C6A2P6DAVPK76WFE4LAM56AZ26N │         │ 127.0.0.1 │         │ 0s     │ 0       │ 0        │ 0 B      │ 0 B       │ 1    │
╰─────┴─────────────────────────┴──────────────────────────────────────────────────────────┴─────────┴───────────┴─────────┴────────┴─────────┴──────────┴──────────┴───────────┴──────╯

╭──────────────────────────────────────────────────────────────────────────────────╮
│                              Connections per server                              │
├──────────────────────────────────────────────────────────┬─────────┬─────────────┤
│ Server                                                   │ Cluster │ Connections │
├──────────────────────────────────────────────────────────┼─────────┼─────────────┤
│ ND5TMCZ32LWFSFQGTMMADGCERCQE4C6A2P6DAVPK76WFE4LAM56AZ26N │         │ 1           │
╰──────────────────────────────────────────────────────────┴─────────┴─────────────╯
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Publish

publish command is a generic data publish utility. This is useful to quickly publish and test without having to write a script.

Usage

nats publish [<flags>] <subject> [<body>]
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Let’s try to publish some data on the subject hello

$ nats publish hello my-data
14:09:46 Published 7 bytes to "hello"
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Note: To publish multiple messages, we can use the --count flag

Subscribe

Similarly to publish command we also have subscribe command which acts as a generic subscription client.

Usage

nats subscribe [<flags>] [<subject>]
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To try out subscribe command first, we will subscribe to the hello subject and then publish some data on the same subject using the nats publish "hello there" command.

$ nats subscribe hello
14:13:20 Subscribing on hello
[#1] Received on "hello"
hi there
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Note: Learn more about publish/subscribe in the distributed communication patterns in NATS article.

Request

request command is a generic request-reply request utility.

Usage

nats request <subject>
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Example

$ nats request hello
14:43:06 Reading payload from STDIN
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Reply

reply command gives us access to the generic service reply utility. The "command" supports extracting some information from the subject the request came in on.

Usage

nats reply <subject> <data>
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Example

$ nats reply hello data
14:48:36 Listening on "hello" in group "NATS-RPLY-22"
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We can also use request/reply together to measure latency. For example, using nats bench --reply and nats bench --request in two terminals at the same time. Then we can invert the number of requests per second to get the latency.

Note: Learn more about request/reply in the distributed communication patterns in NATS article.

KV

NATS KV is a JetStream based Key-Value store. Key-Value stores are specialized NoSQL databases that store values in a data bucket under a specific key.

Config

Before we start storing our key-value pairs, we need to create a config. For this, let’s add a custom my-config. This config helps us create a new bucket with built-in replication.

Note: KV requires JetSteam to be enabled.

$ nats kv add my-config
my-config Key-Value Store Status

         Bucket Name: my-config
        History Kept: 1
       Values Stored: 0
  Backing Store Kind: JetStream
 Maximum Bucket Size: unlimited
  Maximum Value Size: unlimited
    JetStream Stream: KV_my-config
            Storage: File
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PUT and GET

Once we have the config, we have PUT or GET our key-value pairs. In the example below, we will store value myvalue in the key mykey and later retrieve it.

$ nats kv put my-config mykey myvalue
myvalue

$ nats kv get my-config mykey
my-config > mykey created @ 04 Apr 22 11:32 UTC

myvalue
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Bench

bench command might be the most used command. This is basically a benchmark utility that comes with the CLI.

Basic Usage

nats bench [<flags>] <subject>
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Example
Here, we are using the bench command to benchmark our NATS server with 1 million message with 2 publisher and 2 subscribers on the test subject.

$ nats bench --msgs 1000000 --pub 2 --sub 2 test
14:57:01 Starting pub/sub benchmark [subject=test, msgs=1,000,000, msgsize=128 B, pubs=2, subs=2, js=false, pubsleep=0s, subsleep=0s]
14:57:01 Starting subscriber, expecting 1,000,000 messages
14:57:01 Starting subscriber, expecting 1,000,000 messages
14:57:01 Starting publisher, publishing 500,000 messages
14:57:01 Starting publisher, publishing 500,000 messages
Finished      0s [===============================================] 100%
Finished      0s [===============================================] 100%
Finished      0s [===============================================] 100%
Finished      0s [===============================================] 100%

NATS Pub/Sub stats: 7,907,082 msgs/sec ~ 965.22 MB/sec
 Pub stats: 3,060,110 msgs/sec ~ 373.55 MB/sec
  [1] 1,541,921 msgs/sec ~ 188.22 MB/sec (500000 msgs)
  [2] 1,530,055 msgs/sec ~ 186.77 MB/sec (500000 msgs)
  min 1,530,055 | avg 1,535,988 | max 1,541,921 | stddev 5,933 msgs
 Sub stats: 5,275,380 msgs/sec ~ 643.97 MB/sec
  [1] 2,680,372 msgs/sec ~ 327.19 MB/sec (1000000 msgs)
  [2] 2,638,306 msgs/sec ~ 322.06 MB/sec (1000000 msgs)
  min 2,638,306 | avg 2,659,339 | max 2,680,372 | stddev 21,033 msgs
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JetStream

We can also use --js with --pub to publish first and replay using --js --pull and --sub to separately measure the speed of putting and getting messages from the stream.

# Put messages in the stream
$ nats bench --msgs 1000000 --pub 2 test --js

# Pull messages from the stream 
$ nats bench --msgs 1000000 --sub 2 test --js --pull
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Note: We can use the bench command not just to see how fast it goes “all out” but to also generate traffic (using --pubsleep ) and processing times (using --subsleep )

Events

events command shows advisories and events in the NATS server.

$ nats events
Listening for Client Connection events on $SYS.ACCOUNT.*.CONNECT
Listening for Client Disconnection events on $SYS.ACCOUNT.*.DISCONNECT
Listening for Authentication Errors events on $SYS.SERVER.*.CLIENT.AUTH.ERR
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Cheat

cheat is arguably the most awesome command. It helps us see what’s all there is in the NATS CLI in a quick and easy-to-digest format.

$ nats cheat --sections
Known sections:

   account
   bench
   cheats
   consumer
   contexts
   errors
   events
   governor
   kv
   latency
   obj
   pub
   reply
   schemas
   server
   stream
   sub
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Now, we can simply view info about any of the sections like the following:

$ nats cheat account
# To view account information and connection
nats account info

# To report connections for your command
nats account report connections
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Note: We can also use the nats <cmd> --help to get some info about the commands.

Conclusion

In this article, we took a brief look at NATS CLI and learned about some basic CLI commands. This will help us to manage our NATS server easily and any extra dependency! Feel free to reachout if you have any questions.

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