Rocket/site/guide/configuration.md

# Configuration

Rocket aims to have flexible and usable configuration. Rocket applications can
be configured via a configuration file, through environment variables, or both.
Configurations are separated into three environments: development, staging, and
production. The working environment is selected via an environment variable.

## Environment

At any point in time, a Rocket application is operating in a given
_configuration environment_. There are three such environments:

   * `development` (short: `dev`)
   * `staging` (short: `stage`)
   * `production` (short: `prod`)

Without any action, Rocket applications run in the `development` environment.
The environment can be changed via the `ROCKET_ENV` environment variable. For
example, to launch an application in the `staging` environment, we can run:

```sh
ROCKET_ENV=stage cargo run
```

You'll likely need `sudo` for the command to succeed since `staging` defaults to
listening on port `80`. Note that you can use the short or long form of the
environment name to specify the environment, `stage` _or_ `staging` here. Rocket
tells us the environment we have chosen and its configuration when it launches:

```sh
$ sudo ROCKET_ENV=staging cargo run

🔧  Configured for staging.
    => address: 0.0.0.0
    => port: 80
    => log: normal
    => workers: [logical cores * 2]
    => secret key: generated
    => limits: forms = 32KiB
    => tls: disabled
🛰  Mounting '/':
    => GET /
🚀  Rocket has launched from http://0.0.0.0:80
```

## Rocket.toml

An optional `Rocket.toml` file can be used to specify the configuration
parameters for each environment. If it is not present, the default configuration
parameters are used. Rocket searches for the file starting at the current
working directory. If it is not found there, Rocket checks the parent directory.
Rocket continues checking parent directories until the root is reached.

The file must be a series of TOML tables, at most one for each environment, and
an optional "global" table. Each table contains key-value pairs corresponding to
configuration parameters for that environment. If a configuration parameter is
missing, the default value is used. The following is a complete `Rocket.toml`
file, where every standard configuration parameter is specified with the default
value:

```toml
[development]
address = "localhost"
port = 8000
workers = [number_of_cpus * 2]
log = "normal"
secret_key = [randomly generated at launch]
limits = { forms = 32768 }

[staging]
address = "0.0.0.0"
port = 80
workers = [number_of_cpus * 2]
log = "normal"
secret_key = [randomly generated at launch]
limits = { forms = 32768 }

[production]
address = "0.0.0.0"
port = 80
workers = [number_of_cpus * 2]
log = "critical"
secret_key = [randomly generated at launch]
limits = { forms = 32768 }
```

The `workers` and `secret_key` default parameters are computed by Rocket
automatically; the values above are not valid TOML syntax. When manually
specifying the number of workers, the value should be an integer: `workers =
10`. When manually specifying the secret key, the value should a 256-bit base64
encoded string. Such a string can be generated using a tool such as openssl:
`openssl rand -base64 32`.

The "global" pseudo-environment can be used to set and/or override configuration
parameters globally. A parameter defined in a `[global]` table sets, or
overrides if already present, that parameter in every environment. For example,
given the following `Rocket.toml` file, the value of `address` will be
`"1.2.3.4"` in every environment:

```toml
[global]
address = "1.2.3.4"

[development]
address = "localhost"

[production]
address = "0.0.0.0"
```

## Extras

In addition to overriding default configuration parameters, a configuration file
can also define values for any number of _extra_ configuration parameters. While
these parameters aren't used by Rocket directly, other libraries, or your own
application, can use them as they wish. As an example, the
[Template](https://api.rocket.rs/rocket_contrib/struct.Template.html) type
accepts a value for the `template_dir` configuration parameter. The parameter
can be set in `Rocket.toml` as follows:

```toml
[development]
template_dir = "dev_templates/"

[production]
template_dir = "prod_templates/"
```

This sets the `template_dir` extra configuration parameter to `"dev_templates/"`
when operating in the `development` environment and `"prod_templates/"` when
operating in the `production` environment. Rocket will prepend the `[extra]` tag
to extra configuration parameters when launching:

```sh
🔧  Configured for development.
    => ...
    => [extra] template_dir: "dev_templates/"
```

## Environment Variables

All configuration parameters, including extras, can be overridden through
environment variables. To override the configuration parameter `{param}`, use an
environment variable named `ROCKET_{PARAM}`. For instance, to override the
"port" configuration parameter, you can run your application with:

```sh
ROCKET_PORT=3721 ./your_application

🔧  Configured for development.
    => ...
    => port: 3721
```

Environment variables take precedence over all other configuration methods: if
the variable is set, it will be used as the value for the parameter. Variable
values are parsed as if they were TOML syntax. As illustration, consider the
following examples:

```sh
ROCKET_INTEGER=1
ROCKET_FLOAT=3.14
ROCKET_STRING=Hello
ROCKET_STRING="Hello"
ROCKET_BOOL=true
ROCKET_ARRAY=[1,"b",3.14]
ROCKET_DICT={key="abc",val=123}
```

## Configuring TLS

TLS (Transport Layer Security) is configured through the `tls` configuration
parameter. The value of `tls` must be a table with two keys:

  * `certs`: _[string]_ a path to a certificate chain in PEM format
  * `key`: _[string]_ a path to a private key file in PEM format for the
    certificate in `certs`

The recommended way to specify these parameters is via the `global` environment:

```toml
[global.tls]
certs = "/path/to/certs.pem"
key = "/path/to/key.pem"
```

Of course, you can always specify the configuration values per environment:

```toml
[development]
tls = { certs = "/path/to/certs.pem", key = "/path/to/key.pem" }
```

In order for TLS support to be enabled, Rocket must be compiled with the `"tls"`
feature. To do this, add the `"tls"` feature to the `rocket` dependency in your
`Cargo.toml` file:

```toml
[dependencies]
rocket = { version = "0.2.8", features = ["tls"] }
```