# Run settings and app keys

Each part of a deployed app (for example, a website and an API) has its own run settings: how it runs, its memory and CPU, and how many instances run at once. They decide how fast it answers and what it costs.

## The three ways to run [#the-three-ways-to-run]

| Setting | What it does | Good for |
| --- | --- | --- |
| **Sleeps when idle** | Starts when someone visits and costs nothing while idle. The first visit after a quiet spell takes a few seconds. | Internal tools, demos, apps used now and then |
| **Always on, lower price** | Keeps running at a lower price, and may restart now and then. | Apps that should answer at once but can handle an occasional restart |
| **Always on** | Keeps running and is never interrupted. | Busy apps and anything that must not restart |

The AI picks the cheapest way for each part at setup. You can change it any time.

## Before you start [#before-you-start]

- The <Term id="project">project</Term> must be set up to deploy (see [Deploy an app](/docs/deploy/deploy-an-app)).
- To change a setting, you need to be able to change the project.

## See the current settings [#see-the-current-settings]

<ForEveryone>

Open the project on <AppLink to="deploy" /> and go to **Settings**. Each part of the app shows:

- How it runs (one of the three settings above).
- **Memory** and **CPU**.
- **Most instances at once**, with what your plan allows (**Plan allows**).
- The most it can cost: "At most X credits an hour, at full load".

<Callout type="info" title="A ceiling, not a bill">
  The hourly figure is reached only when every instance is busy. Your real spend is in <AppLink to="settings.usage" /> (see [Credits](/docs/workspace/credits)).
</Callout>

The section says where the settings come from: the linked repository's production branch, or the <Term id="studio">Studio</Term>.

</ForEveryone>

<ForDevelopers>

```python
from klarety import Nexus

nx = Nexus.connect()
print(nx.projects.deploy_settings("PROJECT_ID"))
```

Each service lists its mode (`on-demand` for Sleeps when idle, `spot` for Always on, lower price, `always-on` for Always on), its size, its most instances at once, the plan's ceiling for each, and the most it can cost an hour.

</ForDevelopers>

## Change a setting [#change-a-setting]

Ask the project's AI. It edits the deploy setup and pushes it, and the push deploys the change, so the setup stays reviewed and versioned in your code.

<ForEveryone>

<Steps>
<Step>
### Open Settings [#open-settings]
On the project's Deploy page, go to **Settings** and find the part.
</Step>
<Step>
### Ask AI to change it [#ask-ai-to-change-it]
Select **Ask AI to change** and fill in **What should change?**, for example: "Keep the API always on, and let the website sleep when idle." Select **Send**.
</Step>
<Step>
### Watch it work [#watch-it-work]
The app says "Sent to your AI. Watch it work in the Studio." If the Studio is closed, the AI starts when it next opens.
</Step>
</Steps>

<Screenshot src="/docs/_media/deploy-page-overview.png" alt="The Settings section of a project's Deploy page, one row per part of the app" />

</ForEveryone>

<ForDevelopers>

```python
nx.projects.ask_ai_to_deploy(
    "PROJECT_ID",
    "Keep this service always on, with at most 2 instances",
    service="api",
)
```

Leave out `service` to ask about the whole app, for example to set up deploying for the first time.

</ForDevelopers>

## What you see when it worked [#what-you-see-when-it-worked]

A push from the Studio to the production branch waits for a person to approve it (see [Approvals](/docs/deploy/approvals)). Once deployed, **Settings** shows the new setting and cost ceiling.

## Read how each part is doing [#read-how-each-part-is-doing]

Under each part, **Last X days** shows **Calls**, **Errors**, **Average response**, **Busiest moment** (instances at once, of the most allowed), **Wake-up after idle** for a part that sleeps, and **Memory at start**. Use them to decide:

- **Wake-up after idle is too long** for your visitors: switch to **Always on, lower price** or **Always on**.
- **Busiest moment** reaches the most instances allowed: allow more instances, up to what your plan allows.
- **Memory at start** is close to the part's memory: give it more memory before it runs out.

## Rotate the app key [#rotate-the-app-key]

Your live app reaches the project's data with its own **App key**. Only the live app holds it; it is never shown.

<Callout type="warn" title="Rotating stops the old key at once">
  The old key and anything it opened stop working now. The app goes out again with a new key, nothing rebuilt, and may show errors for about a minute.
</Callout>

<ForEveryone>

<Steps>
<Step>
### Open the App key section [#open-the-app-key-section]
Open the project on <AppLink to="deploy" /> and find **App key**.
</Step>
<Step>
### Rotate it [#rotate-it]
Select **Rotate key** and confirm. The app shows **Key rotated**; the live app gets the new key within a minute.
</Step>
</Steps>

<Screenshot src="/docs/_media/deploy-page-overview.png" alt="The App key section on the Deploy page with the Rotate key button" />

</ForEveryone>

<ForDevelopers>

```python
nx.projects.rotate_app_key("PROJECT_ID")
```

</ForDevelopers>

Rotate it whenever you think it leaked. You never copy it anywhere: the app receives it by itself.

## If something goes wrong [#if-something-goes-wrong]

- **"Not priced on your plan yet"**: this setting is not available on your plan yet. Contact us to turn it on.
- **The app ran out of memory**: the deploy explains it. Raise the memory for that part, or make the app use less as it starts.
- **The app did not start answering in time**: if it is slow to start (for example, it loads a large model), load that on first use, or run it always on so it starts once and stays up.

## Where to go next [#where-to-go-next]

- [Deploy an app](/docs/deploy/deploy-an-app)
- [Logs](/docs/deploy/logs)
- [Credits](/docs/workspace/credits)