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package sihl-core
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:
- Resource handles to the database, Memcached, and other backing services
- Credentials to external services such as Amazon S3 or Twitter
- Per-deploy values such as the canonical hostname for the deploy
(Source: https://12factor.net/config)
Configuration
A list of key-value pairs of strings representing the configuration key like SMTP_HOST and a value.
make schema data returns a configuration containing the configuration schema and the configuration data.
val empty : tempty is an empty configuration without any schema or data.
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.
val store : data -> unitstore 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.
root_path contains the path to the project root. It reads the value of ROOT_PATH. If that environment variable is not set, it goes up directories until a .git, .hg, .svn, .bzr or _darcs directory is found. If none of these are found until / is reached, None is returned.
env_files_path contains the path where the env files are kept. It reads the value of ENV_FILES_PATH. If that environment variable is not set, root_path is used. If no root path can be found, None is returned.
read_env_file () reads an .env file from the directory given by env_files_path and returns the key-value pairs as data. If SIHL_ENV is set to test, .env.test is read. Otherwise .env is read. If the file doesn't exist or the directory containing the file can't be found, None is returned.
val read_env_file : unit -> data option Lwt.tval read : ('ctor, 'ty) schema -> 'tyread 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.
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.
read_secret unit returns the value of SIHL_SECRET if it is set. If SIHL_SECRET was not set, it fails in production and in testing or local development the value is set to "secret".
read_int key returns the configuration value with key if present. the first call caches the returned value and subsequent calls are fast.
read_bool key returns the configuration value with key if present. the first call caches the returned value and subsequent calls are fast.
is_test () returns true if Sihl is running in a test environment, meaning if tests are executing parts of Sihl.
is_development () returns true if Sihl is running in a local environment.
is_production () returns true if Sihl is running in a production environment.
val require : ('ctor, 'ty) schema -> unitrequire t raises an exception if the stored configuration doesn't contain the configurations provided by the list of configurations t.
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