I'm going to go further and say that Feature Flags are a nightmare and should be avoided. Because instead of just being used to stage roll-out, they get used to configure different environments for different customers.

You not only waste time with "Remove feature flag X" stories if all customers end up with the feature, you also slow down the response time of some categories of bugs, because you end up having to stop and check the combination of feature flags to reproduce a bug.

And if you end up with a feature that isn't popular except by one customer, not only are you now stuck supporting "Legacy feature Y", you're actually stuck supporting, "Optional legacy feature Y" which is worse.

Maybe I'm ranting about "misuse of feature flags", but I don't like to pontificate about how things ought to be, but how in my experience they actually are.

Yes, it really depends on the type of environment / app you are running too. If your app is stateful, uses lots of data, etc.. then feature flags can cause a lot of issues with inadvertent upgrades that have to be rolled back manually in things like user data.

Or you can have infinite permutations of feature flags if you don't flip them to be on for everyone quickly enough, and it becomes hard to test if[a&(not b)&c&(not d)] behavior vs if[a&b&(not c)&d] and.... you end up with too many to cover with testing well.

They can be very very very nice if you have a lengthy (or perhaps just unpredictable) build/deploy process. And/or if you have lots of teams working independently on the same monolith.

Suppose you have daily production builds. You are rolling out Feature XYZ. You would like to enable it in prod, but you would like to monitor it closely and may need to turn it off again. Feature flags allow that.

Ultimately what's being achieved is a decoupling of configuration and deployment.

    Maybe I'm ranting about "misuse of feature flags", but 
    I don't like to pontificate about how things ought to be, 
    but how in my experience they actually are. 

Similarly, I might just be making excuses for bad build/deploy processes. =)

At my last job we relied heavily on feature flags via Launch Darkly. I will admit: it was somewhat of a band-aid for the fact that our build process was way too slow and flaky, and that we had too many teams working on an overstuffed monolith.

I also use feature flags when I'm 100% sure stakeholders or PMs will somehow find fault a certain feature after it's deployed, even though they're the ones who specified it, approved it and tested it in a staging environment.

Not exactly the thing that we should be using Feature Flags for, but it saved my ass several times.

On the other hand: this removes some of the accountability that non-technical folks have over software. This can be detrimental in the long term.

I have also found that for UIs the best thing to do is have a staged rollout approach.

Internals / Friendly users / Less friendly users / VIPs. The blast radius & intensity of explosion is smaller on the earlier groups.

The groups themselves need not be fixed. If you have a stakeholder/group that demanded the new features, they can be in an early wave. Inevitably they may be the ones to find defects in it, so the sooner the better.

> they get used to configure different environments for different customers

That is not a feature flag, that is a customer configuration option. They are different things and should not be treated in the same way.

Sure, it is possible for a feature flag to behave like a configuration option but they have different lifecycles and different audiences and so should not be confused. Of course it is easy to say that but harder in practice to maintain those differences.

> Seems like many bugs are due to a (production!) user not having the right combinations of flags enabled.

In my experience, feature flags work best if you aim to remove them as quickly as possible. They can be useful to allow continual deployment, and even for limited beta programs, but if you're using them to enable mature features for the whole customer base, they're no longer feature flags.

We've been using feature flags extensively lately. A step that helps for this issue is having all merged code deploy automatically to our QA environment first. We have automated tests which run there regularly, as well as it being the environment most people use for testing, which increases the likelihood that issues like this will become evident quickly.

Definitely doesn't do anything like completely obviate the issue though.