nats.docs/nats_server/configuration.md

Configuration File Format

The NATS server products provide a flexible configuration format that combines the best of traditional formats and newer styles such as JSON and YAML.

The config 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: [...]
• Maps are enclosed in braces: {...}
• Maps can be assigned with no key separator
• Semicolons can be used as terminators

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.
• Can be resolved from the environment variables having the same name

If the environment variable value begins with a number you may have trouble resolving it depending on the server version you are running.

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

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