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config3 - Get Your Settings, No Bananas

How to Use It

  • Define your default configuration in <app_root>/config.default.js
    • This should be a CommonJS module that exports an object which is your application's config values.
    • These should be sensible defaults for local development.
    • You may also use config.default.json, which should be a JSON file.
    • You may also use config.js or config.json
  • If necessary, define local or developer-specific overrides in <app_root>/config.local.js
    • These will take precedence over the defaults
    • Configurations are merged, so you only need to specify the particular values you want to override, not an entirely new configuration.
    • config.local.json or config.local.js will both work
    • Include these file paths in your .gitignore as these are by definition specific to a particular developer or environment and should not be tracked in source control.
  • For deployment, put your configuration overrides in /etc/<package_name>/config.js
    • <package_name> is your npm package name from your project's package.json file
    • /etc/<package_name>/config.json will also work
    • Don't store these in git. This is where your secrets like API keys, database credentials, etc go
  • In any code that needs configuration, just load it
    • var config = require("config3");
    • Your settings will be there.
    • Things get merged and overridden as you would expect. Arrays get replaced. The config-extend module handles this logic for us.
  • config files are loaded with regular old require which looks for .js first and falls back to .json otherwise.
    • Thus the full resolution order, first to last, with last entry winning is:
    • config.default.js OR config.default.json (NOT both)
    • config.js OR config.json (NOT both)
    • config.local.js OR config.local.json (NOT both)
    • /etc/<package_name>/config.js OR /etc/<package_name>/config.json (NOT both)



{"port": 3000, "dbUrl": "mongodb://localhost/myapp", "fbAppId": "12345"}


{"port": 4500}


{"dbUrl": "mongodb://", "fbAppId": "REAL_FB_APP_ID"}

Getting values with the CLI

This module comes with a command line program also called config3 that takes a property path as the only argument and prints out the corresponding value from your application's configuration. This supports property path notation al la db.connection.poolSize via the pathval npm package.

This comes in handy for automating stuff during builds and deployments.

CLI Example

./node_modules/.bin/config3 'emails.admins[0]'

Prints out "" given a config of {emails: {admins: [""]}}

#Motivation and Philosophy

There are many similar modules already written and published to the npm registry. Why yet another? I find problems with most of the existing ones as follows:

  • poisoned by the Ruby on Rails notion of RAILS_ENV=production (NODE_ENV for us)
    • This whole system is flawed and an antipattern
    • The primary way this screws you is as follows:
      • some module you depend on alters its behavior based on NODE_ENV. Typically this might be something like enabling a cache in production but disabling it otherwise.
      • Case in point: express.js will cache views in production only
      • So you set NODE_ENV=staging on your staging system and use one of the npm config packages that loads a staging.yaml file. Now your staging server is way out of alignment with production.
    • So I think this entire notion is fundamentally the wrong way to think about configuration code that looks at NODE_ENV should be removed in favor of explicit options. Packages in npm should assume production-type configuration by default and should allow appropriate changes for development when passed explicit granular options to do development things like enabling source maps, disabling caches, printing debug output, etc.
  • Uses YAML configuration files.
    • YAML is just goofy and rubyish and we shouldn't be bringing it along into the node.js ecosystem. It's been involved in many of ruby's security issues. Just keep your configuration simple. If you need 30 key/value pairs or complicated data structures, paragraphs of comments and logic in your configuration, you are probably building a monolithic monster app that should be split into smaller services.
  • But what about 12 Factor Apps?
    • While mostly I think the 12 factors are quite correct and excellent, when it comes to environment variables, I disagree. Flat files on the filesystem are better as per my blog post Environment Variables Considered Harmful
  • You should have to read 2 or at most 3 files to figure out which values your running application has loaded, which is why I called this module config3


config3 uses the debug package by TJ Holowaychuk. Normally, no debug information is output. To have debug statements written to stdout, set the DEBUG environment variable to config3 or a colon-delimited string containing config3 like

DEBUG=config3 node myapp.js

Notes on Existing Modules

  • config: NODE_ENV, yaml
  • global-config: name says it all. Creates global variables. Fail.
  • config-env Do we really need a JS API to define some key/value pairs?
  • env-config Not a bad choice if you like the 12-Factor environment variable thing, but I personally do not. Also, written in CoffeeScript.
  • json-config No way to have defaults and overrides. Author doesn't know require can load JSON files directly. Throws exceptions.
  • yaml-config YAML. NODE_ENV.
  • feather-config If you think how your config gets built should be a supremely flexible puzzle that you can solve at 2am when production is down, this one actually looks pretty solid to me. If I move away from config3, feather-config would probably be my next choice. It's more complicated than we really want/need so I'd rather have a small number of specific, unchangeable file paths to look at not have configuration values possibly come from as many different places as possible.
  • mods-config No docs. Uses process.cwd().
  • dh-config NODE_ENV
  • lib-config This is just a library, not a full config system.
  • config-node No docs. Repository URL incorrect.
  • nxt-config ini file syntax. Windows. Bitbucket. 2 years stale.
  • config-reader custom, complex config file format
  • local-config Mostly simple and sane. No override capability.
  • context-config Addressing a much more complex problem.
  • pwf-config Not sure what this is.
  • fj-config Looks incomplete.
  • express-config NODE_ENV. package.json incomplete.
  • ...patience ran out

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Get Your Settings, No Bananas







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