Flypper: feature flags, with a GUI

Flypper is a lightweight feature flag package that ships with a WSGI interface.

Installation

Use the package manager pip to install flypper.

pip install flypper

You might want to install one of the following backends instead:

• flypper-redis to store your flags in Redis
• flypper-sqlalchemy to store your flags in a RDBMS using SQL-Alchemy (work in progress)

Why

Feature flags can be instrumental to how a team ships software.

I have a hard take delegating such a critical part to a third-party. Also, third-parties tends to grow a bigger feature set than the one I need, to have a per-seat pricing, and to ask for a SSO tax.

Flypper aims at providing a simple feature flag library one could integrate directly to their application as a dependency. The feature set is purposedly small and will require some light work on your side to integrate.

Differences compared to other similar libraries are:

• A scrappy web UI to manage the flags
• An architecture aimed at being used on backends and front-ends
• An efficient caching mecanism to avoid roundtrip to the database

Usage

The library works with 3 components:

1. A storage backend, storing and retrieving flags in a durable way
2. A client, acting as an efficient in-memory cache for reading flags
3. A context, making flags consistents during its lifespan

Components and their roles

Here is an example:

from redis import Redis

from flypper import Client as Flypper
from flypper_redis.storage.redis import RedisStorage

# Instanciate a *Storage*
redis_storage = RedisStorage(
    redis=Redis(host="localhost", port=6379, db=0),
    prefix="flypper-demo",
)

# Instanciate a *Client*
flypper = Flypper(storage=redis_storage)

# Query flags' statuses within a *Context*
with flypper(segment="professionals") as flags:
    if flags.is_enabled("graceful_degradation"):
        skip_that()
    elif flags.is_enabled("new_feature", user="42"):
        do_the_new_stuff()
    else:
        do_the_old_stuff()

The web UI acts as a client and only needs a storage:

from flypper.wsgi.web_ui import FlypperWebUI

flypper_web_ui = FlypperWebUI(storage=redis_storage)

Web UI

The web UI can then be mounted as you see fit, for instance via DispatcherMiddleware.

app = DispatcherMiddleware(app, {"/flypper": flypper_web_ui})

⚠ Careful, you might need to wrap the FlypperWebUI with your own authentication layer, for instance like here.

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

Please make sure to update tests as appropriate.

Work in progress you can contribute to

• Testing the web UI with pytest and selenium
• Better support prefixes within the web UI, so redirections work
• Write tutorials and recipes in the docs/

Upcoming feature ideas

• Javascript SDK
• Tracking flags usage efficiently
• More storage backends

Credits

Inspiration was heavily taken from the following projects.

• flipper
• unleash
• flipper-client

Many thanks to their authors, maintainers, and contributors.

License

MIT