A zero configuration configuration loader

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A zero configuration configuration loader


// config/common.json
    "port": 9001

// config/production.json
    "redis": {
        "host": "localhost",
        "port": 6379

// server.js
var fs = require('fs')
var fetchConfig = require('zero-config')

var config = fetchConfig(__dirname, {
    dcValue: fs.existsSync('/etc/zero-config/datacenter') ?
        fs.readFileSync('/etc/zero-config/datacenter', 'utf8') :

var port = config.get("port")
var redisConf = config.get("redis")
var redisPort = config.get("redis.port")

You can also call the process with
`node server.js --port 10253` to change the config 
information from the command line


var config = fetchConfig(dirname, opts)

type Keypath : String | Array<String>

type Config : {
    get: (keypath?: Keypath) => Any,
    set: ((keypath: Keypath, value: Any) => void) &
        (value: Any) => void,
    freeze: () => void,
    deepFreeze: () => void,
    clone: () => Config
    getRemote: (keypath?: Keypath) => Any,
    setRemote: ((keypath: Keypath, value: Any) => void) &
        (value: Any) => void

zero-config := (dirname: String, opts?: {
    argv?: Array<String>,
    dcValue?: String,
    blackList?: Array<String>,
    env?: Object<String, String>,
    isStaging?: Boolean,
    seed?: Object<String, Any>,
    defaults?: Object<String, Any>
}) => Config

fetchConfig takes the current dirname as an argument, it assumes that there exists a config folder at ./config in your project and it assumes there exists a common.json and a NODE_ENV.json for each environment.
It returns you a config object with a get(keypath) method to fetch properties out of config. get() takes a keypath, i.e. "prop.nested.someKey"to get direct or nested properties in the config object.
It's recommended you use .get() as in the future we will enable dynamic config properties through flipr support.

The config lookup algorithm

The fetchConfig() function tries to fetch config from multiple locations and then deep merges the objects it finds together into a single object.
Below are the sources it reads in order of least precendence. i.e. the later sources in the list overwrite the earlier ones
  • a defaults object that populates values that have
not been set by any other means.
- a config/common.json JSON file in your project - a config/NODE_ENV.json JSON file in your project - a config/secrets/secrets-NODE_ENV.json JSON file in your project containing secrets per NODEENV but not production - a config/secrets/secrets.json JSON file in your project containing secrets (API keys, OAuth tokens, etc) only for production - a config/NODE_ENV.{datacenter}.json JSON file in your
project if you specificed a datacenter.
- a config/staging.json JSON file in your project if isStaging
option is true
- a config/staging.{datacenter}.json JSON file in your project
if isStaging option is true and you specificed a datacenter.
- a { datacenter: '{datacenter}' } literal if you
specified a datacenter.
- a --config=/var/config/some-file.json JSON file if you
passed a command line argument called `--config` to the
- a object literal based on command line arguments. i.e. if
you pass `--foo='bar' --bar.baz='bob'` you will get
`{ "foo": "bar", "bar": { "baz": "bob" } }`
- a seed object of manual overwrites for testing purposes.
The config loader also uses config-chain for the actual loading logic so you can read their docs


dirname is the directory that is the parent of the config directly. If you call fetchConfig in a file located in the root directory you can just pass __dirname as config lives at ./config.
If you require fetchConfig anywhere else like ./api/server.js you will have to pass path.join(__dirname, '..')


opts is an optional object, that contains the following properties.
Note that opts is only optional in environments other then "production". If your process.env.NODE_ENV is set to "production" then you MUST specifiy opts and specify the opts.dcValue parameter.
Running a production service without knowing how to load datacenter specific configuration is a bug.


opts.dcValue is either null or a datacenter name.
Say you have two datacenters, EC2-west and EC2-east. It's recommended that you have a file called /etc/datacenter that contains either the string EC2-west or EC2-east.
This way any service can know what datacenter it is running in with a simple cat /etc/datacenter.
You can then call fetchConfig(...) with the datacenter value by calling fs.readFileSync('/etc/datacenter')
Note that if you pass the dc config to fetchConfig then the config object will contain the "datacenter" key whose value is either EC2-west or EC2-east or whatever your datacenter names are.
We will also load the file config/production.EC2-west.json and merge that into the config tree.


opts.argv is optional and probably not needed
fetchConfig will read your process argv information using the minimistminimist module.
If you do not want fetchConfig to read global argv for you, you can pass in an argv object with keys like 'foo' and 'bar.baz'' and values that are strings / numbers / booleans


opts.isStaging is an optional boolean value to indicate it is a staging deployment, if set true.
fetchConfig will read staging.json for a staging deployment, followed by staging.{datacenter}.json if datacenter is specified.


opts.blackList is an optional array of argv keys to blacklist.
fetchConfig by default converts all command line arguments to configuration keys. If you want to pass a non config key command line argument like --debug or --restart-fast, etc. then you might want to add them to the blackList
If your opts.blackList is ['debug'] then config.get('debug') will not resolve to the --debug command line argument.


opts.env is optional and probably not needed.
fetchConfig will read the env using process.env. The only property it reads is an environment variable called NODE_ENV.
If you prefer to not have this variable configured through the environment or want to call it something else then you can pass in { NODE_ENV: whatever } as opts.env


should a value be requested from the config using get() and the key does not exist an error will be thrown. By setting opts.loose to true this feature is disabled and a value of undefined is returned should this key not be preset in the config.


opts.seed is optional, it can be set to an object
If it exists we will merge the seed object into the config data we have fetched. seed overwrites all the other sources of configuration.
The seed option is very useful for testing purposes, it allows you to overwrite the configuration that your application would load with test specific properties.
This is an alternative to the NODE_ENV=test pattern, we highly recommend that you do not have a test.json file at all.


opts.defaults is optional, it can be set to an object.
If it exists, it will populate all the values that are unset (but not undefined) in the loaded config with those in opts.defaults.
The difference between defaults and seed is that seed over- writes set values, while defaults does not.

var value = config.get(keypath)

config.get(keypath) will return the value at a keypath. The keypath must be a string.
You can call config.get('port') to get the port value. You can call config.get('playdoh-logger.kafka.port') to get the nested kafka port config option.

config.set(keypath, value)

config.set(keypath, value) will set a value at the keypath.
You can call config.set("port", 9001) to set the port value. You can call config.set("playdoh-logger.kafka.port", 9001) to set then nested kafka port config option.
Note you can also call config.set(entireObject) to merge an entire object into the config instance. This will use deep extend to set all the key / value pairs in entireObject onto the config instance.


Since the config object is supposed to represent a set of static, immutable configuration that's loaded at process startup time it would be useful to enforce this.
Once you are ready to stop mutating config you can call .freeze(). Any future calls to .set() will throw a config frozen exception.
Note that you can always call config.setRemote() as that is not effected by .freeze()


A stricter from of freeze which actually recursively calls Object.freeze() on the config object rendering it immutable.
In strict mode this will throw an error if calling code attempts to mutate the returned config object. A side benefit of this is that it enables config.get() to return the actual object instead of a deep-copy, greatly reducing allocation pressure if your application is fetching large objects out of the config repeatedly.


To get a deep clone of the config object, use config.clone(). A cloned config object will have the same underlying data but none of the other properties. For example, if you clone a frozen config object, you are able to make changes to the clone but not the original object.

var value = config.getRemote(keypath)

The same as config.get() but gets from a different in memory object then config.get().
It's recommended that you use config.get() and config.set() for any local configuration that is static and effectively immutable after process startup.
You can use config.getRemote() and config.setRemote() for any dynamic configuration that is effectively controlled remotely outside your program.

config.setRemote(keypath, value)

The same as config.set() but sets to a different in memory objec then config.set().
You can use config.getRemote() and config.setRemote() for any dynamic configuration that is effectively controlled remotely outside your program.


npm install zero-config


npm test

Best Practices

Zero-config is designed to help you structure your config files to support a number of production concerns. These best practices reflect our approach and some of the reasons we designed Zero-config as we did.
- Configuration should live in a single file - Only put configuration in more specific configuration files when you really have to. Dev and test configs should only contain changes to support development (e.g. turning off caching). - Put your secrets in a secrets.json so that they are easier to manage safely. Ideally never commit these files to your source control repository. This is why we keep secrets in a folder that is easy to symlink - If you must have development secrets in source control for developer convenience then try to scrub them from builds of your projects. We call these secrets-ENV.json to make that easy.


- Raynos - sh1mmer

MIT Licenced

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