[mabbo]

> Make feature flags short-lived. Do not confuse flags with application configuration.

This is my current battle.

I introduced feature flags to the team as a means to separate deployment from launch of new features. For the sake of getting it working and used, I made the mis-step of backing the flags with config files with the intent to get Launch Darkly or Unleash working ASAP instead to replace them.

Then another dev decided that these Feature Flags look like a great way to implement permanent application configs for different subsets of entities in our system. In fact, he evangelized it in his design for a major new project (I was not invited to the review).

Now I have to stand back and watch as the feature flags are being used for long-term configurations. I objected when I saw the misuse- in a code review I said "hey that's not what these are for"- and was overruled by management. This is the design, there's no time to update it, I'm sure we can fix it later, someday.

Lesson learned: make it very hard to misuse meta-features like feature flags, or someone will use them to get their stuff done faster.

[zellyn]

Sadly, this is a battle you are destined to lose. I have almost completely given up. The best you can aim for is to use feature flags better rather than worse.

    - Some flags are going to stay forever: kill switches, load shedding, etc. (vendors are starting to incorporate this in the UI)
    - Unless you have a very-easy-to-use way to add arbitrary boolean feature toggles to individual user accounts (which can become its own mess), people are going to find it vastly easier to create feature flags with per-use override lists (almost all of them let you override on primary token). They will use your feature flags for:
      - Preview features: "is this user in the preview group?"
      - rollouts that might not ever go 100%: "should this organization use the old login flow?"
      - business-critical attributes that it would be a major incident to revert to defaults: "does this user operate under the alternate tax regime?"

You can try to fight this (indeed, especially for that last one, you most definitely should!), but you will not ever completely win the feature flag ideological purity war!

[hamandcheese]

Thank you for this great list of the immense business value derived from "misusing" feature flags!

[sporkland]

We have an interesting hybrid between the two that I'd like your take on. When we release new versions of our web client static assets we have a version number that we bump that moves folks over to the new version.

1. We could stick it in a standard conf system and serve it up randomly based on what host a client hits. (Or come up with more sophisticated rollouts)

2. Or we can put it as "perm" conf in the feature flag system and roll it out based on different cohorts/segments.

I'm leaning towards #2 but I'd love to understand why you want to prohibit long lived keys so I can make a more informed choice. The original blog posts main reasons were that FF systems favor availability over consistency so make a pour tool if you need fast converging global config, which somewhat becomes challenging here during rollbacks but is likely not the end of the world.

[baq]

Or... see them for what they are: runtime configuration. The name implies a use case scenario, but in reality it's just a configuration knob. With a good UI, it's a pretty damn convenient way to do runtime configuration.

So of course they'll be used for long-term configuration purposes, especially under pressure and for gradual rollouts of whole systems, not just A/B testing features.

[rubicon33]

This hits the nail on the head.

The term "feature flag" has come to inherently have a time component because features are supposed to eventually be fulled GA'd.

What I've seen in practice is feature flags are never removed so a better way to think about them is as a runtime configuration.

[mabbo]

There is a need for runtime configurations, yes, but it's important to put them behind an interface intended for that, and not one intended for something else.

[hinkley]

Our FF system uses our config system as its system of record. There's some potential for misuse, and it's difficult to apply deadlines. On the plus side all our settings are captured in version control. Before they were spread out over several systems, one of which had an audit system that was pure tribal knowledge for years.

[gastonfournier]

The main challenge is when things go wrong. Feature flags are designed for high-rate evaluation with low latency responses. Configuration usually doesn't care that much about latency as it's usually read once at startup. This context leads to some very specific tradeoffs such as erring to availability over consistency, which in the case of configuration management could be a bad choice

[zellyn]

Yeah, and assuming they are done well, they probably have better analytics and insights attached to them than anything else except perhaps your experiments!

[hinkley]

Long lived features flags is a development process bug, I'm not sure we can solve it with the feature toggle system.

I'm at the point of deciding that Scrum is fundamentally incompatible with feature flags. We demo the code long before the flag has been removed, which leads to perverse incentives. If you want flags to go away in a timely manner you need WIP limits, and columns for those elements of the lifecycle. In short: Kanban doesn't (have to) have this problem.

And even the fixes I can imagine like the above, I'm not entirely sure you can stop your bad actor, because it's going to be months before anyone notices that the flags have long overstayed their welcome.

I'm partial to flags being under version control, where we have an audit trail. However time and again what we really need is a summary of how long each flag has existed, so they can be gotten rid of. The Kanban solution I mention above is only a 90% solution - it's easy to forget you added a flag (or added 3 but deleted 2)

[gastonfournier]

I faced something similar, and I think it's unavoidable. Give people a screwdriver and they'll find a way of using it as a hammer.

The best you can do is expect the feature flagging solution to give some kind of warning for tech debt. Then equip them with alternative tools for configuration management. Rather than forbidding, give them options, but if it's not your scope, I'd let them be (I know as engineers this is hard to do :P).

[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.

[Dirak]

I feel like this is a solvable problem: 1) make feature flags be configured to have an expiration date. If over the expiration date, auto-generate a task to clean up your FF 2) If you want to be extra fancy, set up a codemod to automatically clean up the FF once it's expired

I don't see the problem with developers using flags for configuration as a stopgap until there's a better solution available.

[tantalor]

> automatically clean up the FF once it's expired

Um what? How could that ever work. It's like you are trying to find new exciting ways to break prod.

[tantalor]

Sounds like "other dev" found some business case they could unblock with existing system, and you thought the business was better off not solving that, or finding a more expensive solution.

Curious how you plan to justify cost to "fix it" to management. If it ain't broke...

[strken]

I think it's better to admit they actually are config, just a different kind of config that comes with an expiration date.

Accepting reality in this way means you'll design a config management system that lets you add feature flags with a required expiration date, and then notifies you when they're still in the system after the deadline.

[timothyfcook]

I agreed. My perspective is that there are two kinds of feature flags: temporary and permanent.

Temporary ones can be used to power experiments or just help you get to GA and then can be removed.

Permanent ones can be configs that serve multiple variations (e.g. values for rate limits), but they can also be simple booleans that manage long term entitlements for customers (like pricing tiers, regional product settings, etc.)

[accountantbob]

We did the same. We were early adopters of unleash and wrangled it to also host long term application configuration and even rule based application config.

The architecture of unleash made it so simple to do in unleash vs having to evaluate, configure, and deploy a separate app config solution.

[gastonfournier]

Victim of your own success. As others were saying, when it works for short-lived its easy/no effort to use it for long-lived configurations.

[ivarconr]

Thanks for sharing. I have seen systems grow in to thousands of flags, where most developers does not know what a particular flags do anymore.

[brightball]

It’s one of the main reasons to start with something like unleash because they have stale flag warnings built in. Plus, since you already have a UI it’s harder for it to be hijacked.

[getrealyall]

The solution is not to use feature flags. Or maybe have them expire. Oh, also, discipline the developers who do this.