Server Config

While the NATS server has many flags that allow for simple testing of features, the NATS server products provide a flexible configuration format that combines the best of traditional formats and newer styles such as JSON and YAML.

Syntax

The NATS configuration file supports the following syntax:

• Lines can be commented with # and //
• Values can be assigned to properties with:
  • Equals sign: foo = 2
  • Colon: foo: 2
  • Whitespace: foo 2
• Arrays are enclosed in brackets: ["a", "b", "c"]
• Maps are enclosed in braces: {foo: 2}
• Maps can be assigned with no key separator
• Semicolons can be used as terminators

The NATS configuration file is parsed with UTF-8 encoding.

Strings and Numbers

The configuration parser is very forgiving, as you have seen:

• values can be a primitive, or a list, or a map
• strings and numbers typically do the right thing
• numbers support units such as, 1K for 1000, 1KB for 1024

String values that start with a digit or a dot '.' can create issues. To force such values as strings, quote them.

Bad Config:

listen: 127.0.0.1:4222
authorization: {
    # BAD!
    token: 3secret
}

Good Config:

listen: 127.0.0.1:4222
authorization: {
    token: "3secret"
}

Variables

Server configurations can specify variables. Variables allow you to reference a value from one or more sections in the configuration. Variables:

• Are block-scoped
• Are referenced with a $ prefix. They have to be unquoted when being referenced, for example an assigment like foo = "$example" will result in foo being the literal string "$example".
• Can be resolved from environment variables having the same name

# Define a variable in the config
TOKEN: "secret"

# Reference the variable
authorization {
    token: $TOKEN
}

A similar configuration, but this time, the value is in the environment:

# TOKEN is defined in the environment
authorization {
    token: $TOKEN
}

The environment variable can either be inlined (below) or previously exported.

TOKEN="hello" nats-server -c /config/file

Include Directive

The include directive allows you to split a server configuration into several files. This is useful for separating configuration into chunks that you can easily reuse between different servers.

Includes must use relative paths, and are relative to the main configuration (the one specified via the -c option):

server.conf:

listen: 127.0.0.1:4222
include ./auth.conf

auth.conf:

authorization: {
    token: "f0oBar"
}

Starting the server only needs to refer to the top-level config containing the include.

nats-server -c server.conf

• Default value: n/a
• Hot reloadable: No

Values

Properties

Connectivity

Centralized Auth

Decentralized Auth

Clustering

Leafnodes

JetStream

Subject Mapping

Logging

Monitoring and Tracing

Runtime Configuration