novi 0.2.0

A simple yet powerful feature flag and multivariate testing platform built in Python

Novi

Table of Contents

1. Concepts
2. Architecture
3. Components
4. Tables
5. Activations (Implementation and Discovery)

Novi is a simple yet powerful feature flag and multivariate testing platform built in Python. Novi is "simple" because all of its core capabilities are built around 2 simple concepts. Flags and Activations

Concepts

Flags

Flags are associated with features. Flags rely on Activations to determine when to turn on or off features. A flag has three attributes:

• A unique ID which is also the primary key for the flag
• A unique name
• A default status.

If the default status is false, the flag is always turned off, irrespective of how the activations get evaluated. In the example below the banner_ad is turned on by default, while the 50% discount coupon is always disabled.

id	name	status
1	banner_ad	true
2	50% discount	false

Activations

Activations determine the status of the flag. Activations can turn a flag on or off when the activation conditions are met. Activations are what make novi a "dynamic" feature flag system, since the activations are evaluated at runtime and enable features to be turned on/off based on runtime scenarios. Some scenarios that Activations are useful:-

• Features could be activated depending on the deployment environment such as production, development or test
• Feature could be shown only to certain usernames and disabled for others.
• Organizations may choose to show a feature to only traffic originating from company IP address ranges during testing
• Features may be shown to a percentage of users selected randomly

The list of scenarios can be infinitely varied and complex. An activation has four attributes:-

• A unique ID,
• A descriptive name,
• A python class name that is used to instantiate an activation object
• A configuration

Activation classes are discovered and registered with Novi using a plugin pattern. Users are expected to provide a folder named "novi_activations" containing modules and packages with Activation classes. An Activation class inherits from the Abstract base class BaseActivation. Out of the box novi comes with 2 activations:-

• A Weighted Random Activation
• A Date/Time based Activation

Each activation object is passed a configuration at the time of instantiation. Configurations enable the business logic that drives activations. Think of configurations as a free-form column, containing strings (typically json) that can be parsed by the Activation class to build its internal configuration object. As an example if your activation turns on/off flags only if current date is between a start date and an end date, you would configure that as shown in the example below (id = 2)

id	name	class_name	config
1	A weighted random activation	novi_activations.standard.weighted_random_activation.WeightedRandomActivation	{ "splits":[100, 0, 0], "variations":["A", "B", "C"]}
2	A date based activation	novi_activations.standard.date_time_activation.DateTimeActivation	{"startDateTime":"11/26/2023 12:00 AM","endDateTime":"11/28/2023 12:00 AM","format": "%m/%d/%Y %I:%M %p"}

See Creating Activations for details on how to create your own custom activations.

Architecture

Tables

Novi captures the details of the above two concepts in just 3 tables: flags, activations and the association table flags_activations.

The tables can be created manually using schema.sql or automatically by setting createTables=True in novi.ini

Components

novi.core

The core component that implements the various model classes, the logic to discover and register activations and the logic to evaluate the final flag status, given a list of activations

novi.client

The client component implements the BaseClient interface and two concrete client implementations that retrieve flags and activations from

• Databases (DbClient)
• Remote API endpoint (RemoteClient)

novi.web

The web component implements a simple flask API server to implement two endpoints

• /flags - Retrieve all flags

• /flags/<flag_name> - Retrieve a specific flag by name

• The web component relies on the DbClient to fetch the flags from a database and expose them via the the /flags resource endpoint

Implementating Activations

Novi scans a folder by name "novi_activations" on the python path and registers all classes inheriting from BaseActivation found within this folder.

class BaseActivation(object):

    def __init__(self, cfg: Any = None):
        self.config = cfg

    def evaluate(self, context: dict = None) -> bool:
        pass

Novi's power comes from being able to implement pretty much any complex logic within these activation classes. A flag can be associated with multiple activations. The final status of the flag is determined by ANDing the status from evaluating each activation.