XPRMNTL (read "Experimental") is an application of Code-based Feature Flags with a web-based configuration via a dashboard and API.

Why is this a thing?

XPRMNTL exists for a number of problems that needed a solution:

1. Feature Flags (Intra-documentationally referred to as "Experiment" or "feature")
   • Gain: Allows us to keep all code in "master" without it being "client-facing"
   • Alternative: version control branches
2. For distributed systems
   • Gain: Allows us to keep all of our instances in sync, where memory is not shared
   • Alternative: a file in the repository that all components use for building
3. That can be quickly changed
   • Gains:
     • Allows rapid enabling/disabling of features (rapid roll-backs on error)
     • Allows gradual scaling that isn't heart-breakingly slow
   • Alternatives:
     • Deploy for changes (5 - 90min)
     • Environment variables for experiments
4. By non-technical people (optionally)
   • Gain: Allows us to wrap metrics around our experiences and allow product ownership to deliver
   • Alternatives:
     • Developer-only configuration and deployment
     • Roll-out meetings
     • After-hours development emergencies for roll-backs
   • Warnings:
     • Make sure testing is done and monitoring is in place if development isn't involved in delivery
     • This is not a use-case for technical replacements (db replacements, etc), but may be for lean startup methodologies of "Build-Measure-Learn"

Components

Dashboard & API

The XPRMNTL dashboard is a UI for the API, which allows you to:

1. Select Github repositories to add to Experiments
2. Modify experiment configuration

The current implementation requires a Github Organization with repositories for the code and uses Github's OAuth2 strategies for authentication/authorization.

Clients

The XPRMNTL client is a language-specific client for "announcing" your experiment configuration and getting back your experiment settings.

Below is a list of available clients. We'd love to see more...

1. Node.js Client
2. Go-lang Client

Plugins

Plugins are for the preferred method of adding additional functionality to either the client or the dashboard (future) Here is a list of the current ones:

1. xpr-express
   • Plugin for Node.js Client
   • Adds some Express middleware.
2. xpr-toggle
   • Plugin for Node.js client, piggy-backs off xpr-exress, as well. Not tested without (volunteers?)
   • Adds a UI toggler to enable/disable features on a per-user basis.
3. xpr-angular
   • Plugin for xpr-toggle
   • Angular Directive for toggling HTML elements when features are enabled

Example App

If you'd like some inspiration implementing XPRMNTL in your own apps, feel free to have a look at the Example App. I currently use it for testing and building new functionality as well, so I'm sorry if I break something for you. It should be stable, at least, at any point.]