Config

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

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

#codestyle