config-chain.md

config-chain

I want to load multiple cascading configuration files

Using config-chain you can load the configuration for your web application from multiple locations. It also cascades the loading so you can load general configuration and overwrite it with more specific configuration.

var path = require("path")
var http = require("http")
var cc = require("config-chain")
var optimist = require("optimist")
var NODE_ENV = process.env.NODE_ENV

// optimist is a useful module to parse command line arguments
// if you run `node example.js --port 8000 --host localhost` then
// argv is { port: 8000, host: 'localhost' }
var argv = optimist.argv

// config loads host & port from your config.json file in the
// config folder. The host & port are overwritten by NODE_ENV
// specific config. This is useful for running a test & local
// server without conflicting ports.
// You can also overwrite the configuration with a hardcoded
// path. You can then just have secret configuration files on
// the production box. Lastly we pass in the argv which allows
// us to overwrite configuration values by passing command line
// arguments to our process!
var config = cc(
    argv,
    '/usr/config/my-app/config.json',
    path.join(__dirname, "config", "config." + NODE_ENV + ".json"),
    path.join(__dirname, "config", "config.json")
).store

// port & host are pretty flexibly defined.
http.createServer(function (req, res) {
    res.end("hello world")
}).listen(config.port, config.host)

Alternatively by hand:

var path = require("path")
var http = require("http")
var fs = require("fs")
var NODE_ENV = process.env.NODE_ENV

var configOpts = [
    '/usr/config/my-app/config.json',
    path.join(__dirname, "config", "config." + NODE_ENV + ".json"),
    path.join(__dirname, "config", "config.json")
]

var config = {}
// loop trick. Asynchronous for loop.
(function loop(callback) {
    // if we have read all files then done
    if (configOpts.length === 0) {
        return callback()
    }

    // do a thing
    var uri = configOpts.pop()
    fs.readFile(uri, function (err, file) {
        if (err) {
            return callback(err)
        }

        var value = JSON.parse(String(file))
        extend(config, value)
        // when we done the thing get the next value of array
        loop(callback)
    })
}(startServer))

function startServer(err) {
    extend(config, parseArguments(process.argv))

    http.createServer(function (req, res) {
        res.end("hello world")
    }).listen(config.port, config.host)
}


function extend(dest, src) {
    for (var k in src) {
        dest[k] = src[k]
    }
}

function parseArguments(args) {
    var opts = {}, key
    args = args.slice(2)

    args.forEach(function (arg) {
        if (arg.substr(0, 2) === '--') {
            key = arg
        } else {
            opts[key] = arg
        }
    })

    return opts
}