Module rocket::config

source ·
Expand description

Server and application configuration.

See the configuration guide for full details.

§Extracting Configuration Parameters

Rocket exposes the active Figment via Rocket::figment(). Any value that implements Deserialize can be extracted from the figment:

use rocket::fairing::AdHoc;

struct AppConfig {
    id: Option<usize>,
    port: u16,

fn rocket() -> _ {


The workers parameter sets the number of threads used for parallel task execution; there is no limit to the number of concurrent tasks. Due to a limitation in upstream async executers, unlike other values, the workers configuration value cannot be reconfigured or be configured from sources other than those provided by Config::figment(). In other words, only the values set by the ROCKET_WORKERS environment variable or in the workers property of Rocket.toml will be considered - all other workers values are ignored.

§Custom Providers

A custom provider can be set via rocket::custom(), which replaces calls to rocket::build(). The configured provider can be built on top of Config::figment(), Config::default(), both, or neither. The Figment documentation has full details on instantiating existing providers like Toml and Env as well as creating custom providers for more complex cases.

Configuration values can be overridden at runtime by merging figment’s tuple providers with Rocket’s default provider:

use rocket::data::{Limits, ToByteUnit};

fn rocket() -> _ {
    let figment = rocket::Config::figment()
        .merge(("port", 1111))
        .merge(("limits", Limits::new().limit("json", 2.mebibytes())));

    rocket::custom(figment).mount("/", routes![/* .. */])

An application that wants to use Rocket’s defaults for Config, but not its configuration sources, while allowing the application to be configured via an App.toml file that uses top-level keys as profiles (.nested()) and APP_ environment variables as global overrides (.global()), and APP_PROFILE to configure the selected profile, can be structured as follows:

use serde::{Serialize, Deserialize};
use figment::{Figment, Profile, providers::{Format, Toml, Serialized, Env}};
use rocket::fairing::AdHoc;

#[derive(Debug, Deserialize, Serialize)]
struct Config {
    app_value: usize,
    /* and so on.. */

impl Default for Config {
    fn default() -> Config {
        Config { app_value: 3, }

fn rocket() -> _ {
    let figment = Figment::from(rocket::Config::default())
        .select(Profile::from_env_or("APP_PROFILE", "default"));

        .mount("/", routes![/* .. */])



  • Rocket server configuration.
  • An identifier (or None) to send as the Server header.
  • A cryptographically secure secret key.


  • Enable or disable coloring when logging.
  • Defines the maximum level of log messages to show.