alt Hacker NewsFeature flags need to be treated as short-lived and experimental otherwise they end up getting abused for everything and make it very difficult to reason about your application.
If it's config/customization, it should be in code. If it's experimental it can be a flag until it solidifies, and then it needs to get moved to code.
When I was at Shopify a couple of years ago they mandated that feature flags had to be short-lived (Like 2-4w lifetime tops, some had exceptions) because they would end up getting left in code and never cleaned up, or for extended periods of time like months. Hard to tell if it's genuinely a "feature flag" or actually just a normal part of the system at that point.
Feature flags being flipped in prod was also a major source of incidents, in part because people didn't treat them as experimental and with the associated risk profile of something experimental.
The only exception where having long-lived flags was useful and required was for operational killswitches (E.g. disable Apple Pay because it's having issues), but that is explicitly not application config.
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I disagree with just about everything you said being a problem except the process of cleaning up is absolutely required.
Notably feature flags triggering incidents is expected and desired vs the alternative of shipping the code and having to roll a release back because there is no other way to remove the feature from prod.
Runtime evaluated feature flags can always be used for control plane levers and emergency handbrakes.
You just have to label them as such and prevent other teams from fiddling with them.
This is not an antipattern, it's just semantic hand-wringing.
My team managed critical systems in the online flow of billions of dollars of daily payment volume. We also wrote the feature flag system that the rest of the company used. Not only were we completely fine with feature flags as long-lived control plane levers, we heavily used the system that way ourselves.
You just have to clearly distinguish between ephemeral rollout flags (and clean them up or expire them) and the permanent control plane levers.
It's the exact same functionality for both sets of tools. Just different practices around the two usages.
Agreed.
This is the kind of design wisdom that’s both true and difficult to win an argument over.
It reminds me of arguments related to over-engineering and complexity. The principles are super important to having a codebase that scales and continues to be efficient to work in as the team grows, but they are hard to objectively measure.
Locally or in isolation something may sound like a great idea. Being able to step back and see the greater ripple effects require some experience and intuition that can’t always be used to convince people otherwise.