Module Core.ConfigurationSource

A module to manage service configurations.

An app’s configuration is everything that is likely to vary between deploys (staging, production, developer environments, etc).

This includes:

(Source: https://12factor.net/config)

Configuration

Sourceexception Exception of string
Sourcetype data = (string * string) list

A list of key-value pairs of strings representing the configuration key like SMTP_HOST and a value.

Sourcetype t

The configuration contains configuration data and a configuration schema.

Sourceval make : ?schema:(unit, 'ctor, 'ty) Conformist.t -> data -> t

make ?schema data returns a configuration containing the configuration schema and the configuration data.

Sourceval empty : t

empty is an empty configuration without any schema or data.

Sourceval data : t -> data

data configuration returns the configuration data of the configuration.

Sourceval commands : t list -> Command.t list

commands configurations returns the list of CLI commands given a list of configurations.

Storing configuration

Configuration might come from various sources like .env files, environment variables or as data provided directly to services or the app.

Sourceval store : data -> unit

store data stores the configuration data.

A configuration is a list of key-value string pairs.

Reading configuration

Using the schema validator conformist it is easy to validate and decode configuration values. Conformist schemas can express a richer set of requirements than static types, which can be used in services to validate configurations at start time.

Validating configuration when starting services can lead to run-time exceptions, but they occur early in the app lifecycle. This minimizes the feedback loop and makes sure, that services start only with valid configuration.

project_root_path contains the path to the root of the project/app. Its value is known at app start, thus not requiring it to be a function. It reads the value of PROJECT_ROOT_PATH. If that env variable is not set, it reads the current working directory of the process.

Sourceval project_root_path : string

read_env_file () reads an .env file from the project root directory and returns the key-value pairs as data. If SIHL_ENV is set to testing, .env.testing is read. Otherwise .env is read. If the file doesn't exist, empty data is returned.

Sourceval read_env_file : unit -> data Lwt.t
Sourceval read : (unit, 'ctor, 'ty) Conformist.t -> 'ty

read schema returns the decoded, statically typed version of configuration t of the schema. This is used in services to declaratively define a valid configuration.

The configuration data t is merged with the environment variable and, if present, an .env file.

It fails with Exception and prints descriptive message of invalid configuration.

Sourceval read_string : string -> string option

read_string key returns the configuration value with key if present. The function is memoized, the first call caches the returned value and subsequent calls are fast.

Sourceval read_int : string -> int option

read_int key returns the configuration value with key if present. the first call caches the returned value and subsequent calls are fast.

Sourceval read_bool : string -> bool option

read_bool key returns the configuration value with key if present. the first call caches the returned value and subsequent calls are fast.

Sourceval is_testing : unit -> bool

is_testing () returns true if SIHL_ENV is set to testing.