flipper

This is a stab at implementing the outward facing part of a hypothetical feature flipping system. The model allows you to selectively enable and disable features at any level (global, version, group, and user), although admin tools to manage this have not been built.

This part of the system is a simple HTTP server exposing a REST API with a single endpoint that calculates on the fly what features are available for a user taking into account what features are enabled/disabled across all entities related to that user. And it does it pretty quickly.

Notes:

• it's a python async app.
• all calculations are done inside redis as set operations (via a lua script)
• it does not deal with the admin side of managing these feature flags, it simply calculates and serves them efficiently.
• ideally a separate part of the system would be responsible for the CRUD admin side.
• because of that we need to write to redis manually in order to test it.
• the endpoint expect a GET request with QS parameters representing user/request identifiers (user, group, version, etc). These should be validated upstream.
• the model uses a dual positive and negative flag schema, that should give reasonably fine control over enabling and disabling features. The main rule is that negative flags take precedence over positive flags.
• So a feature is available for a user if it's explicitly set for any of the provided identifiers (user, group, version, etc) and not explicitly disabled for any of those identifiers.
• the model chosen does not take into account any hierarchy of the different types of identifiers (user, group, version, global, etc).
• see the tests for some examples

Examples

Let's enable 2 feature flags for version v1, and disable(override) one of them for group g1:

$ echo "SADD version:v1:positive feature_A feature_B\nSADD group:g1:negative feature_B" | redis-cli

For example here we see that there are 2 enabled features for version v1, for an anonymous user:

$ curl "http://localhost:5000?version=v1"

{"features": ["some_feature_A", "some_feature_B"]}

But if were to pass in a user/group identifiers, we see that this particular user only has 1 enabled feature:

$ curl "http://localhost:5000?version=v1&group=g1&user=some_user"

{"features": ["some_feature_A"]}

We can also selectively activate a feature for group g1

$ echo "SADD group:g1:positive special_g1_feature" | redis-cli

$ curl "http://localhost:5000?version=v1&group=g1&user=some_user"
{"features": ["feature_A", "special_g1_feature"]}

Installation

# create and activate a python 3.6 virtualenv
python3 -m venv venv
source venv/bin/activate

# install python package
make install-develop

Test

make test

Run local server

make dev-server

Some benches

$ echo "GET http://localhost:5000?user=1&group=g2&version=v1" | vegeta attack -duration=10s -workers=10 -rate=100 | vegeta report
Requests      [total, rate]            1000, 100.10
Duration      [total, attack, wait]    9.992770575s, 9.989999969s, 2.770606ms
Latencies     [mean, 50, 95, 99, max]  2.637319ms, 2.78229ms, 3.220638ms, 3.587132ms, 4.734117ms
Bytes In      [total, mean]            26000, 26.00
Bytes Out     [total, mean]            0, 0.00
Success       [ratio]                  100.00%
Status Codes  [code:count]             200:1000