This package provides a mechanism that allows operators to enable and disable experimental or transitional features at deployment time. These flags should be able to govern the behavior of the application starting as early as possible and should be available to every component such that decisions may be made based on flags at the component level.

Feature gates must be defined and registered with the global registry in an init() function. This makes the Gate available to be configured and queried with a default value of its Enabled property.

const myFeatureGateID = "namespaced.uniqueIdentifier"

func init() {
	featuregate.Register(featuregate.Gate{
		ID:          fancyNewFeatureGate,
		Description: "A brief description of what the gate controls",
		Enabled:     false,
	})
}

The status of the gate may later be checked by interrogating the global feature gate registry:

if featuregate.IsEnabled(myFeatureGateID) {
	setupNewFeature()
}

Note that querying the registry takes a read lock and accesses a map, so it should be done once and the result cached for local use if repeated checks are required. Avoid querying the registry in a loop.

Feature gates can be enabled or disabled via the CLI, with the --feature-gates flag. When using the CLI flag, gate identifiers must be presented as a comma-delimited list. Gate identifiers prefixed with - will disable the gate and prefixing with + or with no prefix will enable the gate.

otelcol --config=config.yaml --feature-gates=gate1,-gate2,+gate3

This will enable gate1 and gate3 and disable gate2.

Features controlled by a Gate should follow a three-stage lifecycle, modeled after the system used by Kubernetes:

1. An alpha stage where the feature is disabled by default and must be enabled through a Gate.
2. A beta stage where the feature has been well tested and is enabled by default but can be disabled through a Gate.
3. A generally available stage where the feature is permanently enabled and the Gate is no longer operative.

Features that prove unworkable in the alpha stage may be discontinued without proceeding to the beta stage. Features that make it to the beta stage will not be dropped and will eventually reach general availability where the Gate that allowed them to be disabled during the beta stage will be removed.