Configuration

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.

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.

Note

The NATS configuration in the file can also be rendered as a JSON object (with comments!), but to combine it with variables the variables still have to be unquoted.

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 can create issues. To force such values as strings, quote them.

BAD Config:

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

Fixed 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

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

export 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

Note that include is not followed by = or :, as it is a directive.

auth.conf:

authorization: {
    token: "f0oBar"
}

> nats-server -c server.conf

Configuration Properties

Connectivity

Connection Timeouts

Limits

JetStream

You can enable JetStream in the server’s configuration by simply adding a jetstream {} map. By default, the JetStream subsystem will store data in the /tmp directory, but you can specify the directory to use via the store_dir, as well as the limits for JetStream storage (a value of 0 means no limit).

Here’s an example minimal file that will store data in a local “nats” directory with some limits.

$ nats-server -c js.conf

# js.conf
jetstream {
   store_dir=nats
   // 1GB
   max_memory_store: 1073741824
   // 10GB
   max_file_store: 10737418240
}

Normally JetStream will be run in clustered mode and will replicate data, so the best place to store JetStream data would be locally on a fast SSD. One should specifically avoid NAS or NFS storage for JetStream. Note that each JetStream enabled nats-server should use its own individual storage directory.

Authentication and Authorization

Centralized Authentication and Authorization

Decentralized Authentication and Authorization

The Configuration options here refer to JWT based authentication and authorization.

Runtime Configuration

Monitoring and Tracing

Configuration Reloading

A server can reload most configuration changes without requiring a server restart or clients to disconnect by sending the nats-server a signal:

nats-server --signal reload