Config vs Setting vs Feature flag


Config needs restart to be updated, static, stored in file, override by env variable, small number of config

Example: DB config, server listen port, remote host location

Feature flag

Feature flag and settings can be changed at runtime without restart or down time. Both are similar but I want to draw a bold line separate them.

Feature flag is temporary, has to be clean up or removed someday in the future. It is about roll out, release, use context to decide who, when, where, which version to enable which can be apply to users partially, or globally. It is usually controlled by engineers, or technical operation team.


Setting is permanently. It has been designed to be in the code without creating technical debt.

It likes a feature which has a real user use case for example to adjust behavior of the system.

It should be safe to be uses, changes, enables, disables in numerous times. It should be test throughout.

Any feature flags that has been rolled out and stable, can be transitioned to setting such as kill switch.

Example: Site title, User role & Permission, Look & feel, Content to be shown

Below is a comparison table:

Config Feature flag Setting
When to changes Before start Runtime Runtime
Lifetime Temporary/Permanently Temporary Risky, moderate tested
Safety Very safe, well tested Permanently Safe, well tested
User Engineer/Operator Engineer/Operator Normal user
Affects Global/All users Partial/Global Global/Depends on each feature
Tech Debt Low High Medium
Amount of configurable Low High Medium
Rate of changes Rarely Occationally On demand