Manage stack policies

A policy is a lifecycle rule you attach to a stack. Where a forma declares what resources should exist, a policy declares how formae manages the stack over time on its own, without you running apply again. There are two:

TTL: destroy the stack after a duration, for ephemeral environments.
Auto-reconcile: re-apply the declared state on an interval, so drift never sticks.

You attach a policy one of two ways:

Inline, declared directly on a single stack. It belongs to that stack and is deleted with it.
Reusable (standalone), defined once with a label and referenced from any number of stacks. Edit it in one place and every stack that references it picks up the change.

The Policy concept covers the trade-offs in full. This guide shows how to attach both kinds.

CLI
AI assistants

Attach an inline policy

Add a policies listing to the stack. A TTL policy expires it after a duration:

new formae.Stack {
  label = "dev-environment"
  description = "Ephemeral dev workspace"
  policies = new Listing {
    new formae.TTLPolicy {
      ttl = 4.h
      onDependents = "abort"
    }
  }
}

Or keep the stack pinned to its declared state with auto-reconcile:

policies = new Listing {
  new formae.AutoReconcilePolicy {
    interval = 5.min
  }
}

Declare the policy inside your stack’s complete forma, alongside its resources. Reconcile compares the whole stack, so applying a forma that holds only the policy would remove the stack’s resources.

Share one policy across stacks

To apply the same rule to several stacks, give the policy a label and define it once at the top of the forma, then reference it from each stack with .res:

local ephemeral = new formae.TTLPolicy {
  label = "ephemeral-24h"
  ttl = 24.h
  onDependents = "abort"
}

forma {
  ephemeral

  new formae.Stack {
    label = "dev-sandbox-1"
    description = "Sandbox for the payments team"
    policies = new Listing { ephemeral.res }
  }

  new formae.Stack {
    label = "dev-sandbox-2"
    description = "Sandbox for the checkout team"
    policies = new Listing { ephemeral.res }
  }
}

Change ttl in the one definition and both stacks pick it up on the next apply.

Apply

formae apply --mode reconcile your-infra.pkl

  formae apply · reconcile                                                                          your-infra.pkl
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  + 3 create

  ▌ Policies
  Operation ▲   Label                                   Type                Stack
  + create      ephemeral-24h                           ttl
  + create      ephemeral-24h                           ttl                 dev-sandbox-1
  + create      ephemeral-24h                           ttl                 dev-sandbox-2

────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  ↑↓: select  space: expand  →←: column  s: sort  y: confirm  q: abort This operation will create 1 policy(ies).  Do
you want to continue? (y/N)  ?: help

The plan shows the policy being created and attached to each stack (for the reusable example above, create policy ttl ephemeral-24h, then attach ephemeral-24h to dev-sandbox-1 and attach ephemeral-24h to dev-sandbox-2). From then on formae enforces it: TTL destroys the stack when the duration elapses; auto-reconcile hard-reconciles on every interval.

Verify

Reusable policies and the stacks they are attached to show in:

formae inventory policies

  formae inventory
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
                                         ╭────────────╮
  1 Resources    2 Targets    3 Stacks   │ 4 Policies │
─────────────────────────────────────────╯            ╰─────────────────────────────────────────────────────────────

Label ▲             Type                AttachedStacks
──────────────────────────────────────────────────────────────────────
ephemeral-24h       ttl                 dev-sandbox-1, dev-sandbox-2

Showing 1 of 1 policies
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  /: query
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  ↑↓/j/k: navigate  enter: detail  /: search  s: sort  r: refresh  1-4: tab  q: quit                       ?: help

Inline policies have no independent identity, so to see the policy on a given stack, check the stack itself:

formae inventory stacks

  formae inventory
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
                             ╭──────────╮
  1 Resources    2 Targets   │ 3 Stacks │   4 Policies
─────────────────────────────╯          ╰───────────────────────────────────────────────────────────────────────────

Label ▲                   Description                                     Policies
──────────────────────────────────────────────────────────────────────────────────────────────────────────────
dev-sandbox-1             Sandbox for the payments team                   TTL: 1d, expires in 23h58m (ephemer…
dev-sandbox-2             Sandbox for the checkout team                   TTL: 1d, expires in 23h58m (ephemer…

Showing 2 of 2 stacks
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  /: query
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
  ↑↓/j/k: navigate  enter: detail  /: search  s: sort  r: refresh  1-4: tab  q: quit                       ?: help

With the formae MCP plugin connected, describe the lifecycle you want and let the assistant define the reusable policy and attach it to each stack:

Conversation

You

Create a reusable 24-hour TTL and attach it to both the dev-sandbox-1 and dev-sandbox-2 stacks.

Assistant

I simulated it first. It creates one ttl policy, ephemeral-24h (24 hours, onDependents = abort), then attaches it to dev-sandbox-1 and dev-sandbox-2. Each stack is destroyed 24 hours after the policy attaches, and editing the one policy updates both. Apply it?

You

Yes.

Assistant

Done. ephemeral-24h now covers both sandboxes. Attach it to another stack any time by pointing that stack at the same policy.

A TTL with onDependents = "cascade" deletes resources in other stacks if they depend on this one, anywhere the dependency chain leads. Use the default abort unless you are certain nothing outside the stack should survive it.

Get started

Guides

Concepts

Reference

Manage stack policies

See also

​See also

See also