Feature flag
A feature flag is a configuration control that conditionally enables, disables, or selects a software feature or behavior.
Platform Engineering on Kubernetes
A feature flag is a runtime-controlled configuration mechanism that enables or disables application functionality without changing or restarting the application.
- How it is used
- Separates deployment of new service code from decisions about when its features become available to customers.
- How deep it goes
- Works through multi-service flag variants and an SDK evaluation call, while leaving storage and provider management to the platform capability.
- Examples
- Uses FEATURE_DEBUG_ENABLED, a Conference eventsEnabled flag with three variants, and an OpenFeature ObjectValue call.
- What you can do after
- Apply it via OpenFeature to evaluate a shared flag and change a running Conference application's behavior without restarting components.
Read how Platform Engineering on Kubernetes explains feature flag →
Infrastructure as Code, Patterns and Practices: With examples in Python and Terraform
A feature flag is a Boolean-controlled configuration mechanism that enables or disables a feature, resource, dependency, or attribute.
- How it is used
- Stages, tests, and hides infrastructure changes before applying them to production or exposing them to collaborators.
- How deep it goes
- Demonstrates definition, defaulting, conditional references, activation, and removal, but does not detail configuration-manager implementation.
- Examples
- Uses Python, JSON, Terraform, and CloudFormation examples to switch server modules and load-balancer membership.
- What you can do after
- Apply it via infrastructure as code to stage changes and limit their immediate impact on existing resources.
Django in Action
A feature flag is a conditional control that enables or disables application functionality according to configuration or runtime criteria.
- How it is used
- Limits production risk by exposing new functionality only to selected users.
- How deep it goes
- Explains conditional rollout, three Waffle control types, installation, configuration, migrations, and activation checks.
- Examples
- Uses Waffle switches for global rollout, samples for percentage rollout, and flags for role, account, language, or group targeting.
- What you can do after
- Apply feature rollouts via Django Waffle using switches, samples, and flags.
Learn Rust in a Month of Lunches
A feature flag is a configuration option that conditionally enables code, dependencies, or capabilities during compilation.
- How it is used
- Controls which optional crate code and capabilities compile, helping projects avoid compiling functionality they do not use.
- How deep it goes
- Explains defaults, Cargo.toml syntax, compiler visibility, and source-level cfg gating, but does not develop flag implementation beyond these examples.
- Examples
- Uses reqwest's blocking client, Cargo feature listings, cargo add, Cargo.toml entries, and compiler errors for unavailable APIs.
- What you can do after
- Operate/configure Cargo dependencies by inspecting feature lists and enabling required crate functionality explicitly.
Read how Learn Rust in a Month of Lunches explains feature flag →
The AI Pocket Book
A configuration mechanism that controls which users see a given version of a feature.
- How it is used
- Uses controlled user exposure to make trunk-based deployment safer.
- How deep it goes
- Explains staged exposure and final switchover, but does not detail flag implementation or management.
- Examples
- Uses old-versus-new code paths, developers, and quality-assurance staff as the staged rollout example.
- What you can do after
- Operate/configure staged releases that validate new features before exposing them to every user.
Think Like a Software Engineering Manager
A feature flag is a runtime control that enables or disables a software feature without requiring a new release.
- How it is used
- Controls production features during phased releases, experiments, and incident response.
- How deep it goes
- Explains uses, benefits, A/B testing, and cleanup responsibilities but does not describe implementation mechanics.
- Examples
- Uses hidden buttons, percentage-based user assignment, customer-use analysis, and emergency feature deactivation.
- What you can do after
- Operate controlled production launches, experiments, and feature deactivation with lower release risk.
Read how Think Like a Software Engineering Manager explains feature flag →
GitHub Actions in Action: Continuous integration and delivery for DevOps
A feature toggle is a runtime-controlled switch that selectively enables or disables a software capability independently of deployment.
- How it is used
- Separates deployment from release so capabilities can be exposed, validated, or withdrawn independently.
- How deep it goes
- Explains switch-based old/new code selection, production validation, rollback, and gradual exposure without prescribing a flagging system.
- Examples
- Uses old-versus-new code switching and a monitored canary rollout through successive user rings.
- What you can do after
- Operate/configure it to stage production exposure and restore prior behavior by disabling a switch.
Code Like a Pro in Rust
A feature flag is a Cargo configuration option that enables or disables optional functionality, dependencies, or code.
- How it is used
- Configures optional crate capabilities, dependency features, conditional compilation, and stable-versus-nightly support.
- How deep it goes
- Explains Boolean feature definitions, dependency propagation, cfg integration, and trade-offs, but stops short of exhaustive Cargo semantics.
- Examples
- Uses serde, base64, SIMD, architecture backends, Cargo manifests, cfg-gated imports, and nightly compiler attributes.
- What you can do after
- Operate/configure Cargo features and conditional Rust code while evaluating compile-time, binary-size, compatibility, and maintenance trade-offs.
Related concepts
- rollbackused by · Rollback is the reversal or discarding of changes to restore data, software, or system state to an earlier or otherwise valid state.
- strangler patternused by · The strangler pattern is an incremental modernization approach that replaces a legacy system by gradually transferring its functionality to a new system until the legacy system can be retired.
- OpenFeatureused by · OpenFeature is an open standard and API for consuming and evaluating feature flags independently of the underlying provider.
- model architecturepart of · The structural organization of a computational system’s components, relationships, and operations that determines how it processes information or behaves.
- text-to-speech conversionconfigures · Text-to-speech conversion is the computational synthesis of spoken audio from written text.
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