What is NATs

What are the different things you can do with NATs?

Publish

NATs lets you send messages to a subject. Like a HTTP request it takes a body and headers.

Subscribe

NATs also lets you subscribe to subjects. It gets the body, headers from a publish request and can process the message and send a reply a reply subject specified within the message.

Reply Subjects

Every message comes with a reply subject; it creates a short lived subscription to a randomly generated inbox. This allows a subscription to know where to send a response and creates the publish / subscribe pattern.

Demonstration one - send to anything

Create a subscriber -> nats sub "*" --queue="rpc" Publish a message -> nats pub rpc/hello/there 'hello there'

Catch all will see everything that comes in and tell you the endpoint it is coming from.

Using / in the subject name stops you from doing many things

Sub - nats sub "rpc/>" --queue="rpc" -> this should let you see any messages that start with rpc/ and end with anything else Pub nats pub rpc/hello/there 'hello there' -> see it doesn't work

Changing them to dots allows you to do this.

Sub - nats sub "rpc.>" --queue="rpc" Pub - nats pub rpc.hello.there 'hello there' -> receives message

Tools NATs provides to accomplish this

Authentication Types

NATs has a few ways to authenticate a connection to the server. I'm going to focus on one of the easier ones of username / password but other options include: token, NKey, File Credentials and TLS. When setting your username and password you connect to the NATs cluster; it will check its user configuration to understand what the connection has permission to.

Authorisation

Lets give to a problem we are solving

We have 3 main services apart of Twist

• RGS - This is our key API all traffic goes through here.
• Game Engines - these are all the same except with different names. They give a bet result from the game to give to the RGS.
• RNG server - This generate our random numbers for the game.

We have these rules that we must achieve

• RGS can send requests to Game. -- subject
• RGS can receive replies from the Game Engine.
• RGS can reply to a Game.
• Game can send replies to the RGS
• Game can send request to the RGS
• Game can send request to the RNG
• Game can receive replies from RNG

Little inbox issues to also be aware of

• _INBOX.> allows you to connect to every inbox and listen to subscribe to other inboxes RESPONSE messages
• _INBOX.{servicename}.> - Making your subscribe subject for inboxes helps protect against this.
• _INBOX.> is needed for publish permissions unless you map all the other services that will send messages to this users subscription. A lot of effort.

A few commands:

nats sub "rpc.>" --user=god --password=god nats sub "_INBOX.>" --user=god --password=god

nats sub "" --user=rng --password=ExQDVTjkJvpNpNvC6k6Ly0qVzF3OvoODXG39Bdzv nats sub "rpc." --user=rng --password=ExQDVTjkJvpNpNvC6k6Ly0qVzF3OvoODXG39Bdzv nats sub "rpc.1_1_97.play" --user=rng --password=ExQDVTjkJvpNpNvC6k6Ly0qVzF3OvoODXG39Bdzv

nats sub "rpc.rng.integers" --user=rng --password=ExQDVTjkJvpNpNvC6k6Ly0qVzF3OvoODXG39Bdzv

nats pub rpc.hello.there 'hello there' --user=god --password=god nats pub rpc.rng.integers 'hello there' --user=god --password=god

nats pub rpc.rng.integers 'hello there' --user=rgs --password=t7sueqyO1PU14utllwe3hJSPVX0sqP7e9xljNyga