Introduction to Flags

Confidence Flags is a managed service for feature flagging. It provides sophisticated targeting and coordination capabilities.

In Confidence, a flag is a way to control what experience a user should receive. A flag has multiple variants, one for each intended experience, and these variants describe the specifics of the experience.

This video gives a quick overview of how feature flags work in 2 minutes and 2 seconds.

Clients resolve flags to decide which experience to serve to a user. Common types of clients are mobile apps, web sites, and backend services. A set of rules define what variant to assign to which users in what situations. The resolver evaluates the rules and decide which variant to return to the client using data in the evaluation context. The evaluation context is data about the user, such as their country, age, or subscription status, and the environment the client is running in, such as the browser type. The client feeds the context to the resolver in the resolve request. If the context meets a rule’s targeting condition, the client receives the variant specified in the rule.

Flag Anatomy

A flag has a name and a value. In Confidence, the flag value is a structure with named properties. Think of it as a JSON object. This makes it possible to control multiple aspects of the behavior of a client with a single flag. Flags have a schema that describe the structure of the value: available properties and their data types. Variants give a name to a value of the flag which defines a possible behavior of the thing the flag is controlling.

Imagine a flag that controls the various aspects of the Spotify’s home screen. The flag has a name, home-screen, and the value has properties:

• The size of the title (title-font-size).
• Show the settings button or not (show-settings).
• Show shortcuts or not (show-shortcuts).
• Number of shortcuts to show (shortcut-count).

The schema for this flag is as follows:

Property	Type	Description
title-font-size	String	Size of the title font.
show-settings	Boolean	Whether to show the settings button.
show-shortcuts	Boolean	Whether to show shortcuts.
shortcuts-count	Integer	How many shortcuts to show.

The flag has two variants: default and large-title. The default variant has the following values:

Property	Value
title-font-size	"small"
show-settings	true
show-shortcuts	true
shortcuts-count	9

The large-title variant has the following values:

Property	Value
title-font-size	"large"
show-settings	false
show-shortcuts	true
shortcuts-count	6

With the flag and its variants in place, a client can resolve the flag to a value. For example, a website can resolve the flag to the large-title variant, and show a large title, hide the settings button, and show six shortcuts.

When you use a flag to control an experience, the flag is applied and the client emits a flag applied event. The resolver writes flag applied events, in the form of assignment decision records, to a data warehouse for later use in analysis of experiments.

Client Types

Resolving a flag to value and applying the flag value to control an experience are two distinct operations. The type of client decides when these operations happen.

Single-user clients, such as mobile apps or single-page web applications, resolve multiple flags (1, 2) at the start of a session. They later use locally cached flag values when using flags throughout the session. The reason for this is to reduce flickering of the user experience during the session. When using a flag, the client emits an event (3) that says the flag value was applied. If a client resolves a flag at the start of the session but never used it, it doesn’t emit an event. The resolver writes a flag applied event to a data warehouse for later use in analysis of experiments (4).

Multi-user clients, such as backend services, resolve flags as requests come in (1). Since the clients use flag values directly when rendering the response, the resolve and apply operations happen at the same time. Use the option (apply: true) in the resolve request to Confidence to apply the flag as the client resolves it (1, 3). As a consequence, the resolver writes a flag applied event to a data warehouse for later use in analysis of experiments (2).

If you are using one of Confidence Flags SDKs then you don’t have to worry about the details of the resolve and apply operations. The SDKs take care of this for you.

Learn more about the concepts of Confidence Flags:

Confidence SDKs

Confidence provides SDKs for flag resolving with support for multiple languages and platforms. More information about the Confidence SDKs is available in the dedicated section.