[llbeansandrice]

> Give people a screwdriver and they'll find a way of using it as a hammer.

I feel like feature flags aren't that far off though. They're fantastic for many uses of runtime configuration as mentioned in another comment.

There's multiple people in this thread complaining about "abuse" of feature flags but no one has been able to voice why it's abuse instead of just use beyond esoteric dogma.

[bluefirebrand]

Allow me to try:

Feature Flags inherently introduce at least one branch into your codebase.

Every branch in your codebase creates a brand new state your code can run through.

The number of branches introduced by Feature Flags likely does not scale linearly, because there is a good chance they will become nested, especially as more are added.

Start with even an example of one feature flag nested inside another. That creates four possible program states. Four is not unreasonable, you can clearly define what state the program should be in for all four states.

Now scale that to a hundred feature flags, some nested, some not.

It becomes impossible to know what any particular program state should be past the most common configurations. If you can't point to a single interface in a program and tell me all of the possible states of it, your program is going to be brittle as hell. It will become a QA nightmare.

This is why Feature Flags should be used for temporary development efforts or A/B testing, and removed.

Otherwise you're going to have a debugging nightmare on your hands eventually.

Edit: Note that this is different from normal runtime configurations because normally runtime configurations don't have a mix of in-dev options and other temporary flags. Also, they aren't usually set up to arbitrarily add new options whenever it is convenient for a developer.

[baq]

Sorry, not buying it.

Branches are difficult to reason about? Yes, I agree.

Are branches necessary to make the product behave in a different way in some circumstances? Most of the time.

Do those circumstances require a branch? Unless you’re super confident about some part of code, yes? But why would you be?

Runtime configuration is not about making QA easy. It’s introduced because QA has been hell already so you can control rollout of code which you know wasn’t properly QA’d - or it was but turns out the thing you built isn’t the thing users want and the release cycle is too long to deploy a revert.

I’d say ‘branches are bad but alternatives are worse’.

[bluefirebrand]

There is nothing worse than code with dozens to hundreds of possible configuration states that you must test for every new feature.

If your QA was bad before, you've made it worse.

"I can toggle it off without pushing a new release" is a terrible bandaid for the problem.

[x0x0]

The fundamental diff between feature flags and config is the former is meant to be a soft deploy of code where everyone is expected to eventually be on the new code. Thus it should have a timer built in where it stops, and you should consider all new customers launching with it on.

As for why: if you don't deprecate the feature flag in some time span, you're permanently carrying both code paths. With ongoing associated dev and qa resources and costs against your complexity budget.

Permanent costs should only be undertaken after careful consideration, and should be outside the scope of a single dev deciding to undertake them. Whereas flags should be cheap to add to enable dev to get stuff into prod faster while retaining safety.

Permanently making something a config choice should be done after heavier deliberation because of the aforementioned costs, and you often want different tools to manage it. Including something heavier duty than a single checkbox/button in your internal CS admin tooling. These are often tied into contracts or legal needs, and in many cases salesforce should be the source of truth for them. Or whatever CPQ system you're using.