🏰 What is NATS?
The text below is mostly taken from the official NATS docs NATS is a high-performance messaging system written in Golang. NATS is very easy to use, has very high bandwidth, and easily scales. It has 48 well-known clients, 11 of which are supported by the maintainers. NATS offers delivery guarantees, high availability, and fault tolerance. NATS is used on the web, IoT, and blockchain.
Subject¶
Subject in NATS is like a topic for Kafka or URL for HTTP. At its simplest, a subject is just a string of characters that form a name that publishers and subscribers can use to find each other.
Subject Hierarchies¶
For example, a world clock application might define the following to logically group related subjects:
time.us
time.us.east
time.us.east.atlanta
time.eu.east
time.eu.warsaw
Wildcards¶
NATS provides two wildcards that can take the place of one or more elements in a dot-separated subject. Subscribers can use these wildcards to listen to multiple subjects with a single subscription but publishers will use a fully specified subject, without the wildcard.
Matching a single token¶
The first wildcard is * which will match a single token. For example, if an application wanted to listen for eastern time zones, they could subscribe to time.*.east, which would match time.us.east and time.eu.east.
Matching multiple tokens¶
The second wildcard is > which will match one or more tokens, and can only appear at the end of the subject. For example, time.us.> will match time.us.east and time.us.east.atlanta, while time.us.* would only match time.us.east since it can't match more than one token.
Monitoring and wire taps¶
Subject to your security configuration, wildcards can be used for monitoring by creating something sometimes called a wire tap. In the simplest case, you can create a subscriber for >. This application will receive all messages - again, subject to security settings - sent on your NATS cluster.
Mix wildcards¶
The wildcard * can appear multiple times in the same subject. Both types can be used as well. For example, *.*.east.>will receive time.us.east.atlanta.