# Scaling

> How much compute a replica has, how many replicas an app may run, how many requests a replica takes at once, and where the app runs.

Scaling has three parts: the size of one replica, the number of replicas, and the region. Size and replicas are under **Scaling**. A change applies with the next deployment.

## Instance size

The size is the CPU and memory of each replica. It is billed per second while the replica runs.

| Size | CPU | Memory |
| --- | --- | --- |
| Starter | 1 vCPU | 512 MB |
| Small | 1 vCPU | 1 GB |
| Medium | 2 vCPUs | 2 GB |
| Large | 4 vCPUs | 4 GB |

Start small. If the runtime log says the app ran out of memory, choose the next size.

## Replicas

A replica is one running copy of your app. **Replicas** sets how many may run at once.

Replicas start when traffic arrives and stop when it goes quiet. With a maximum of 3, a quiet app runs one replica, or none while it sleeps, and a busy one runs up to three.

How many replicas an app may have depends on your plan. See [Pricing](https://arrangic.com/pricing).

> **More than one replica**
>
> Replicas do not share memory or files. Keep sessions and other state in a database or a store outside the app, and guard work that must happen once with a lock in your own code.

## Concurrent requests per replica

Another replica starts once every running one handles this many requests at the same time. Leave it empty and the size decides:

| Size | Requests at the same time |
| --- | --- |
| Starter | 25 |
| Small | 25 |
| Medium | 50 |
| Large | 100 |

Lower it if each request is heavy. Raise it if requests are light and mostly wait.

## Sleep

Whether an idle app sleeps is set here too, with **Keep one replica always on** and **Wake up fast**. See [Sleep and wake](https://arrangic.com/docs/sleep-and-wake.md).

## Region

The region is where your app runs. You choose it when you create the app, from regions in North and South America, Europe, Africa, Asia and Oceania. Pick the one closest to your visitors, or to your database.

The region cannot be changed later. To move an app, create a new one in the other region.

## What the overview shows

**Overview** shows what each replica is doing right now, and CPU, memory, requests and response time for the last 24 hours.

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This page on the site: https://arrangic.com/docs/scaling  
All pages of the documentation: https://arrangic.com/llms.txt