Skip to main content

Feature Flags

EmailEngine supports feature flags that allow you to enable or disable specific features at startup. Feature flags are controlled via environment variables and are primarily used for experimental or optional functionality.

How Feature Flags Work​

Feature flags are set using environment variables with the prefix EENGINE_FEATURE_:

EENGINE_FEATURE_<NAME>=true

Enabling a feature:

Set the value to any of these (case-insensitive): y, yes, 1, t, true

EENGINE_FEATURE_EXAMPLE=true
EENGINE_FEATURE_EXAMPLE=1
EENGINE_FEATURE_EXAMPLE=yes

Disabling a feature:

Set the value to any other value, or remove the environment variable entirely:

EENGINE_FEATURE_EXAMPLE=false
EENGINE_FEATURE_EXAMPLE=0
EENGINE_FEATURE_EXAMPLE=no

Name Formatting​

Feature names are normalized internally -- hyphens, underscores, and spaces are treated as underscores:

# These all refer to the same feature:
EENGINE_FEATURE_MY_FEATURE=true
EENGINE_FEATURE_MY-FEATURE=true

Startup Logging​

When feature flags are enabled, EmailEngine logs them at startup:

{"msg":"Enabled feature flags","featureFlags":["my_feature"]}

Configuration Examples​

.env file:

EENGINE_FEATURE_NEW_UI=true

Docker Compose:

environment:
  - EENGINE_FEATURE_NEW_UI=true

Command line:

EENGINE_FEATURE_NEW_UI=true emailengine

Usage Notes​

Feature flags are used internally to gate experimental functionality. The available flags may change between EmailEngine versions. When a feature flag is not recognized by the current version, it is silently ignored.

Feature flags require an application restart to take effect -- they cannot be changed at runtime.

See Also​