> ## Documentation Index
> Fetch the complete documentation index at: https://docs.formae.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Policy

> A policy is a lifecycle rule you attach to a stack: automatic cleanup after a duration, or automatic enforcement of declared state.

A policy is a configurable behavior you attach to a stack. Where a forma declares what resources should exist, a policy declares how formae should manage the stack's lifecycle over time, without you having to run another `apply`.

formae has two built-in policy types:

* **[TTL policy](/documentation/concepts/policies/ttl)**: destroys a stack and its resources after a set duration.
* **[Auto-reconcile policy](/documentation/concepts/policies/auto-reconcile)**: re-applies the stack's declared state at a fixed interval, undoing out-of-band and incremental changes.

## Inline vs. reusable policies

You can define a policy two ways.

**Inline policies** live directly inside a stack definition. They belong to that stack alone and are deleted along with it.

```kotlin theme={"languages":{"custom":["/languages/pkl.json"]}}
new formae.Stack {
  label = "dev-environment"
  policies = new Listing {
    new formae.TTLPolicy {
      ttl = 4.h
      onDependents = "cascade"
    }
  }
}
```

**Reusable policies** are standalone objects, defined once and referenced from any number of stacks with `.res`. Changes to the policy propagate to every stack that references it.

```kotlin theme={"languages":{"custom":["/languages/pkl.json"]}}
local ephemeralPolicy = new formae.TTLPolicy {
  label = "ephemeral-1h"
  ttl = 1.h
  onDependents = "abort"
}

forma {
  ephemeralPolicy

  new formae.Stack {
    label = "dev-stack-1"
    policies = new Listing { ephemeralPolicy.res }
  }

  new formae.Stack {
    label = "dev-stack-2"
    policies = new Listing { ephemeralPolicy.res }
  }
}
```

| Aspect    | Inline                 | Reusable                                |
| --------- | ---------------------- | --------------------------------------- |
| Label     | None                   | Required                                |
| Lifecycle | Deleted with the stack | Independent, must be explicitly deleted |
| Sharing   | Single stack only      | Any number of stacks                    |
| Use case  | One-off behavior       | Consistent policy across stacks         |

<Tip>
  Reach for a reusable policy as soon as you find yourself copying the same `ttl` or `interval` value into more than one stack. A single source of truth means one edit updates every stack that uses it.
</Tip>

## Querying policies

```bash theme={"languages":{"custom":["/languages/pkl.json"]}}
formae inventory policies
```

Lists reusable policies only, since inline policies have no independent identity outside their stack. To see which policy, inline or reusable, is attached to a given stack, check the stack itself:

```bash theme={"languages":{"custom":["/languages/pkl.json"]}}
formae inventory stacks
```

## See also

* [TTL policy](/documentation/concepts/policies/ttl): automatic cleanup after a duration.
* [Auto-reconcile policy](/documentation/concepts/policies/auto-reconcile): automatic enforcement of declared state.
* [Stack](/documentation/concepts/stack): the unit a policy attaches to.