---
title: Introduction
description: What Acropolis is, why we built it, and what it supports.
sidebar:
  icon: book-open
---

Acropolis turns an app's source code into an OCI image with no Dockerfile and no daemon. It is a single Rust binary, `acropolis`, licensed Apache-2.0 or MIT, and it is the builder behind [Olimpia](https://olimpia.dev).

## Status

:::caution[Experimental]
Acropolis is experimental software. In practice that means:

- The CLI flags, the `--events json` schema, `info.json` keys and exit codes may change between minor releases while the version is `0.x`. Every change is listed in the [changelog](https://github.com/olimpiacloud/acropolis/blob/main/CHANGELOG.md).
- Detection follows Railpack's rules, but a new release can pick a different runtime base or install plan for the same app. [`acropolis plan`](/usage#plan) shows what it will do before building.
- It only runs on Linux, as root, and the build sandbox is not a VM boundary. Read [Running in production](/production) before building untrusted code.

Pin a version, keep a fallback builder for apps it cannot build (exit code `78`), and report what breaks in [GitHub issues](https://github.com/olimpiacloud/acropolis/issues).
:::

## Why

On a PaaS every build starts on an empty machine, and the tools available there were slow, heavy, or produced huge images:

- **Cold builds are slow.** In our benchmark Railpack takes 54 to 170 s because it first downloads its builder image, and BuildKit does not retry a download that hangs: we saw a 68 MB layer download at 200 KB/s for 10 minutes. Docker is faster, but only if someone wrote a multi-stage Dockerfile by hand.
- **Images are bloated.** Railpack leaves devDependencies, the cache and its toolchain manager in the image: a sample Next app weighs 345 MB against 105 MB with a well-made Dockerfile.
- **A lot of memory for little work.** Railpack uses more than 2.9 GB of RAM to build an Express server with 7.5 MB of dependencies.
- **Rebuilds reuse nothing.** With Docker, changing one line of a Go app recompiles everything (41 s).
- **No cache survives on an ephemeral builder.**

What came out of it is in [Benchmarks](/benchmarks), and how it gets there in [How it works](/how-it-works).

## What it supports

| ecosystem | image runtime |
| --- | --- |
| Node: npm, pnpm, yarn 1, yarn berry, bun; Next, Nuxt, Astro, SvelteKit, Remix, React Router, TanStack Start, Angular, Vite, Nx, Turborepo | distroless with a minimal shell when possible; otherwise `node:<version>-bookworm-slim`. Next standalone, Nitro, SPA on Caddy |
| Bun | `distroless/cc` + bun, or Debian slim |
| Go | `distroless/static` |
| Rust | `distroless/cc` |
| Python: uv, poetry, pdm, pipenv, pip | `python:<version>-slim` |
| Ruby, PHP/Laravel, Java, .NET, Elixir, Gleam, Deno, C/C++ | the official slim image of each one |
| Static sites and scripts | Caddy, Debian slim |

It honors `railpack.json` and `acropolis.json`: see [Configuration](/configuration). Apps with a Dockerfile are out of scope: keep building those with BuildKit.