# Feature Flags

> Rolls a Feature out to 5%, 25%, 50% or every user, and turns it off in one click. A bad deploy reaches only the share that has it.

Feature Flags turn a piece of behaviour on for a share of users without a new deploy, as LaunchDarkly and Unleash do.

## When to place it

- Place it as soon as you ship often and roll back rarely, because the flag makes every Feature its own small canary. It unlocks with [Feature flags](https://wiki.playquorum.dev/research/feature-flags.md) in Seed, for 800 ◇, after [Continuous delivery](https://wiki.playquorum.dev/research/ci.md).
- Skip it when you have no Features worth staging. It is cheap and carries nothing, so that is the only question.

## How it works

It carries no traffic. It limits how far a [Bad deploy](https://wiki.playquorum.dev/incidents/bad-deploy.md) reaches. A bad deploy fails **8% of App Server requests for each Feature** its batch shipped, up to the ceiling its deploy strategy sets. A Feature behind a flag only breaks the share of users the flag has reached.

Each shipped Feature has a rollout: **dark, 5%, 25%, 50%, or every user**. A Feature with no step set is live for everyone, which is what a Design with no Feature Flags Node does with all of them.

| Deploy strategy | Ceiling on the blast radius | Thirteen Features with no flags | Thirteen Features at 5% |
| --- | --- | --- | --- |
| Recreate | 100% | everything breaks | 5.2% breaks |
| Rolling | 40% | 40% breaks | 5.2% breaks |
| Blue-green | 10% | 10% breaks | 5.2% breaks |
| Canary | 5% | 5% breaks | 5% breaks (its own ceiling) |

The flag is a ceiling of its own, so it wins over the strategy: Recreate cannot outrun a 5% rollout.

## Options

- **Rollout step**: dark, 5%, 25%, 50%, or every user, set per Feature. A lower step limits the blast radius and nothing else.

## How it fails

- **The code still ships.** A deploy ships the code around its Features too. A batch with no Feature still breaks one Feature's worth, and a Design whose Features are all dark still runs the code that is not behind a flag.
- **The rollout is not a load switch.** A Feature still earns and still costs capacity at 5%. Only the blast radius follows the flag.
- **No lift, no holdout.** The users without the Feature do not measure it yet. That waits on `ab-testing`.
- **Flags left behind.** A Feature turned off still pays its upkeep, and a flag at 100% is dead weight. Remove takes the code out for good and ends the upkeep.

### [Bad deploy](https://wiki.playquorum.dev/incidents/bad-deploy.md)

- **Signs:** The **Bad deploy** bar appears at the top of the board, and the error rate jumps right after a deploy.
- **Do now:** Set the Features in the last deploy to **Off** on the Feature Flags card, so a bad deploy of them breaks nobody. Click **Roll back** on the bar too, if you own [Continuous delivery](https://wiki.playquorum.dev/research/ci.md).
- **Prevent:** Keep new Features at 5% for a deploy before you move them on, and research [Automated tests](https://wiki.playquorum.dev/research/testing-culture.md).

## Tips

- Keep a Feature at 5% for a deploy, then move it on. A flag at 100% is a flag you can delete.
- Turn a Feature **Off** when a Bad deploy's bar names it. That is the one click the mitigation toolbox promises.
- Remember that a flag on a Feature that is not in the current batch changes nothing until the next deploy ships it.

## Rules

- Each further copy costs 25% more than the one before.
- Selling it refunds 50% of what its last copy cost.
- It has one size.

## Research next

Once you own Feature flags, these Research items build on it.

[A/B testing](https://wiki.playquorum.dev/research/ab-testing.md), [Graceful degradation](https://wiki.playquorum.dev/research/graceful-degradation.md)

## Facts

Feature Flags
- **Code:** ff
- **Real product:** LaunchDarkly
- **Group:** Platform
- **Unlocked by:** [Feature flags](https://wiki.playquorum.dev/research/feature-flags.md)
- **Era:** [Seed](https://wiki.playquorum.dev/eras/seed.md)
- **Place:** $150 first copy
- **Burn:** $0.01/s
- **Sizes:** 1
- **Overhead:** —
- **Takes:** —
- **Sends:** —

## See also

- [Feature flags](https://wiki.playquorum.dev/research/feature-flags.md)
- [Components](https://wiki.playquorum.dev/components.md)

Source: https://wiki.playquorum.dev/components/ff