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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

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.
  • 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

Property Description Default
host Host for client connections. 0.0.0.0
port Port for client connections. 4222
listen Listen specification <host>:<port> for client connections. Either use this or the options host and/or port. same as host, port
client_advertise Alternative client listen specification <host>:<port> or just <host> to advertise to clients and other server. Useful in cluster setups with NAT. Advertise what host and port specify.
tls Configuration map for tls for client and http monitoring.
cluster Configuration map for cluster.
gateway Configuration map for gateway.
leafnode Configuration map for a leafnode.

Connection Timeouts

Property Description Default
ping_interval Duration at which pings are sent to clients, leaf nodes and routes. In the presence of client traffic, such as messages or client side pings, the server will not send pings. Therefore it is recommended to keep this value bigger than what clients use. "2m"
ping_max After how many unanswered pings the server will allow before closing the connection. 2
write_deadline Maximum number of seconds the server will block when writing. Once this threshold is exceeded the connection will be closed. See slow consumer on how to deal with this on the client. "2s"

Limits

Property Description Default
max_connections Maximum number of active client connections. 64K
max_control_line Maximum length of a protocol line (including combined length of subject and queue group). Increasing this value may require client changes to be used. Applies to all traffic. 4Kb
max_payload Maximum number of bytes in a message payload. Reducing this size may force you to implement chunking in your clients. Applies to client and leafnode payloads. 1Mb
max_pending Maximum number of bytes buffered for a connection Applies to client connections. 64Mb
max_subscriptions Maximum numbers of subscriptions per client and leafnode accounts connection. 0, unlimited

Authentication and Authorization

Centralized Authentication and Authorization

Property Description
authorization Configuration map for client authentication/authorization.
accounts Configuration map for multi tenancy via accounts.

Decentralized Authentication and Authorization

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

Property Description
operator Path to an operator JWT.
resolver Resolver type MEMORY or URL(<url>) for account JWTs. (When the operator JWT contains an account URL, it will be used as default. In this case resolver is only needed to overwrite the default.)
resolver_tls tls configuration map for tls connections to the resolver. (This is for an outgoing connection and therefore does not use timeout, verify and map_and_verify)
resolver_preload Map to preload account public keys and their corresponding JWT. Keys consist of <account public nkey>, value is the <corresponding jwt>. Only used when resolver=MEMORY.

Runtime Configuration

Property Description Default
disable_sublist_cache If true disable subscription caches for all accounts. This is saves resources in situations where different subjects are used all the time. false, cache enabled
lame_duck_duration In lame duck mode the server rejects new clients and slowly closes client connections. After this duration is over the server shuts down. Start lame duck mode with: nats-server --signal ldm. "2m"

Monitoring and Tracing

Property Description Default
server_name The servers name, shows up in logging. Defaults to the server's id. Generated Server ID
trace If true enable protocol trace log messages. Excludes the system account. false, disabled
trace_verbose If true enable protocol trace log messages. Includes the system account. false, disabled
debug If true enable debug log messages false, disabled
logtime If set to false, log without timestamps true, include timestamp
log_file Log file name, relative to... No log file
log_size_limit Size in bytes after the log file rolls over to a new one 0, unlimited
max_traced_msg_len Set a limit to the trace of the payload of a message. 0, unlimited
syslog Log to syslog. false, disabled
remote_syslog Syslog server address.
http_port http port for server monitoring.
http Listen specification <host>:<port>for server monitoring.
https_port https port for server monitoring. This is influenced by the tls property.
https Listen specification <host>:<port>for TLS server monitoring.
system_account Name of the system account. Users of this account can subscribe to system events. See System Accounts for more details.
pid_file File containing PID, relative to ... This can serve as input to nats-server --signal
port_file_dir Directory to write a file containing the servers open ports to, relative to ...
connect_error_reports Number of attempts at which a repeated failed route, gateway or leaf node connection is reported. Connect attempts are made once every second. 3600, approx every hour
reconnect_error_reports Number of failed attempt to reconnect a route, gateway or leaf node connection. Default is to report every attempt. 1, every failed attempt

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