Config Wrangler Scripts

Load Etcd v3 keys, environment vars, and command line arguments in a predictable, standardized way.

I was searching for a simple, lightweight and standardized way to import config into projects, and to my surprise I couldn't find anything like that. So, I'm working on creating a collection of modules or includes for various languages I work in, in order to standardize the way that things are done.

Main goals:

Load variables from Etcd v3, environment variables, command line arguments.
Be extremely light weight, and have few or no dependencies.
Simplify origin of keys in Etcd and Env. Each project should have it's own namespace, nothing shared.
Predictable outcome between each language Config Wrangler is written in.
Ability to reload sources by calling load function again.
If the language supports async, have a watch function notify when a change occurs.

By using this module, variables are read from these sources in this order:

Etcd v3 keys
Environment variables
Command line arguments

Variables are overridden if they are redefined during that order. Meaning that if variable "port" is defined in Etcd, it can be overridden by ENV, and both Etcd and ENV can be overridden by command line argument. The key format is standardized, as to further reduce guesswork. Etcd keys are pretended by namespace, and are "lower-kebab-case". Environment variables are are prepended by namespace, and are "UPPER_SNAKE_CASE". Command line arguments are "lower-kebab-case", starting with "--". The config-wrangler module returns all keys as "camelCase", normalizing how config appears in code.

Examples

Hypothetical web project is configured as so in Python or PHP:

# Python...
from configWrangler import configWrangler
config = configWrangler({
    'etcdNameSpace': 'cfg/web-service/',
    'envNameSpace': 'WEBSVC',
    'requiredKeys': ['port', 'serverName', 'maxConnects']
})

// PHP...
include_once('./configWrangler.php');
$config = configWrangler(array(
    'etcdNameSpace' => 'cfg/web-service/',
    'envNameSpace' => 'WEBSVC',
    'requiredKeys' => array('port', 'serverName', 'maxConnects')
));

Config is now available to project from three different sources:

Etcd key	Env key	CLI key	Code result
cfg/web-service/port	WEBSVC_PORT	--port	config['port']
cfg/web-service/server-name	WEBSVC_SERVER_NAME	--server-name	config['serverName']
cfg/web-service/max-connects	WEBSVC_MAX_CONNECTS	--max-connects	config['maxConnects']
cfg/web-service/time-out-ms	WEBSVC_TIME_OUT_MS	--time-out-ms	config['timeOutMs']

# Assuming Etcd has all of the above keys configured,
# they can be overridden by ENV by doing:
export WEBSVC_MAX_CONNECTS=100
export WEBSVC_SERVER_NAME="New staging server"
python someScript.py

# Or as a one-time env set
WEBSVC_PORT=8080 python someScript.py

# And they can be overridden again by using CLI arguments:
python someScript.py --max-connects=50 --server-name="Test server"

The configuration is now agnostic of the language of the script/service. The example above could have been PHP, Python or Node.js, being configured the same way.

Config object options

Key	Required	Description
etcdNameSpace	No	Namespace/prefix to search for keys in Etcd
envNameSpace	No	Namespace/prefix to search for keys in local environment
etcdApiPath	No	Etcd V3 JSON proxy is currently at "/v3alpha". Option is here if it changes

Other languages

Config Wrangler is available for the following languages:

Python (this project)
PHP (this project)
Node.js/JavaScript

Notes