I've worked at Sabre some time ago and we used feature flags intensively. Feature was enabled/disabled using our own configuration server (which was used to co

I've worked at Sabre some time ago and we used feature flags intensively. Feature was enabled/disabled using our own configuration server (which was used to configure many other things) - it was basically a dynamic file with booleans, that we could turn on/off. After the feature was released we removed the if statement from the code.