source-configs

A Node.js module that harvests app-level config values from command line arguments, environment variables, or config files based on a config schema you define within your app. This module was built and is maintained by the Roosevelt web framework team, but it can be used independently of Roosevelt as well.

Configs matching a given schema are sourced from the following locations in the following order of precedence:

Command line argument set in the schema via commandLineArg.
Environment variable set in the schema via envVar.
Deployment config file declared via:
- Command line argument: --deploy-config-file or --df.
- Environment variable: DEPLOY_CONFIG.
- package.json as a deployConfig field.
Default defined in the schema.

Usage

First declare source-configs as a dependency in your app.

Then create a config schema JSON object to tell source-configs what config values to listen for.

Here's a simple example declaring that our application will use a WebSocket with a configurable host, port, and protocol:

// your-schema-js-file.json
{
  websocket: {
    host: {},
    port: {},
    protocol: {}
  }
}

Schema metadata

Schemas support the following metadata for each configurable property in order to create constraints if desired or add additional functionality:

description [String]: Describe what this config will be used for.
default [any]: Set a default value for this config. If not set, the default is null.
values [Array]: Enumerated list of values that are valid. If not set, any value will be valid.
commandLineArg [String|Array]: Command line argument(s) to listen for that will set this config. If not set, source-configs will not listen for command line arguments to set the value for this config.
envVar [String|Array]: Environment variable(s) to listen for that will set this config. If not set, source-configs will not listen for an environment variable to set the value for this config.

User Defined Functions

Additionally, a schema can be a function which has the parent config passed to it as the first argument. To do this create a key/value pair within the schema object:

If the schema is stored in a .js file, set the key as the desired function name and the value as the function.
If using a .json file to store the schema, set the key as the desired function name and the value as 'user defined function'. Once the .json file is required in, override the key's value with the desired function.

Below is a more complex WebSocket config example leveraging all of the above metadata options:

// your-schema-js-file.json
{
  websocket: {
    host: {
      description: 'WebSocket host URL',
      default: 'localhost',
      commandLineArg: ['--websocket-host-url', '--ws-host', '-h'],
      envVar: ['WEBSOCKET_HOST_URL', 'WS_HOST']
    },
    port: {
      description: 'WebSocket port',
      default: 8081,
      commandLineArg: ['--ws-port', '-p'],
      envVar: 'WS_PORT'
    },
    protocol: {
      description: 'Which WebSocket protocol',
      values: ['ws', 'wss'],
      commandLineArg: '--ws-protocol',
      envVar: 'WS_PROTOCOL'
    },
    url: 'user defined function'
  }
}

Use in your app

Here's an example usage of source-configs using the schema defined above:

const sourceConfigs = require('source-configs')
const schema = require('./your-schema-js-file.json')
schema.websocket.url = function (config) {
  return config.protocol + '://' + config.host + ':' + config.port
}
const config = sourceConfigs(schema)

// access one of the configs
console.log(config.websocket.port)

Properties of source-configs module

In addition to its constructor, source-configs exposes the following properties: