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

# Builds

> Details about the environment your app is built in

Shuttle builds run on AWS CodeBuild, where we compile your Rust app and place it in a Shuttle `runtime` Debian-based Docker image.

## Build architecture

Shuttle builds and runs images for the Arm64 (aarch64) architecture by default. Pro+ users can reach out to Shuttle Support if they require the x86\_64 architecture.

## Builder image

The Rust builder image is based on [cargo-chef](https://github.com/LukeMathWalker/cargo-chef) to utilize Docker-layer caching of the build dependencies.

### Rust toolchain

The Rust version in the image is regularly updated to the latest `stable-aarch64-unknown-linux-gnu` toolchain (or `stable-x86_64-unknown-linux-gnu` depending on your project's build architecture).

By default, the `wasm32-unknown-unknown` target is installed, which enables compiling WASM frontends.

### External tools

Apart from what is already found in the Debian-based cargo-chef image [\[1\]](https://github.com/debuerreotype/docker-debian-artifacts/blob/bfa3d175e4153a23ffb4cf1b573d72408333b4e2/bookworm/rootfs.manifest) [\[2\]](https://github.com/docker-library/buildpack-deps/blob/fdfe65ea0743aa735b4a5f27cac8e281e43508f5/debian/bookworm/Dockerfile), these `apt` packages are also installed:

* `clang`
* `cmake`
* `llvm-dev`
* `libclang-dev`
* `mold`
* `protobuf-compiler`

Additionally, these tools are installed:

* `cargo-binstall` (latest)
* `trunk` (0.19.2)

<Tip>Some other build tool you think we should add? Let us know!</Tip>

## Customize build process

### Feature flags

Use [the "shuttle" feature flag](/docs/project-configuration#cargo-feature-flags) for custom behavior when building on Shuttle.

### Environment variables

The `SHUTTLE=true` env var is set in the builder image.

If you have build flags or env variables that need to be set during compilation, you can add them in `.cargo/config.toml` ([docs](https://doc.rust-lang.org/cargo/reference/config.html)) and include it in your deployment. Below are some examples.

```toml .cargo/config.toml theme={null}
[build]
rustflags = ["--foo", "bar"]

[env]
MY_ENV_VAR = "Shuttle to the moon! 🚀🚀🚀"
```

## Runtime image

The runtime image that your built executable is placed in is a `bookworm-slim` (Debian 12) with `ca-certificates` and `curl` installed.

## (EXPERIMENTAL) Hook scripts

<Warning>This feature is experimental and can change</Warning>

There are three optional bash scripts that can be used to run custom commands during the build.
Create them at the root of your project.

* `shuttle_prebuild.sh`: Runs before `cargo build`. Can be used to install custom build dependencies.
* `shuttle_postbuild.sh`: Runs after `cargo build`.
* `shuttle_setup_container.sh`: Runs in the runtime image before build artifacts are copied into it. Can be used to install custom runtime dependencies.

### Example: Install a custom Rust toolchain

In this example, we install and switch to the `nightly` toolchain.

```sh shuttle_prebuild.sh theme={null}
rustup install nightly --profile minimal
rustup default nightly
```

### Example: Install a build dependency

```sh shuttle_prebuild.sh theme={null}
apt update
apt install -y libopus-dev
```

### Example: Build a WASM frontend

```sh shuttle_postbuild.sh theme={null}
cd frontend
trunk build --release
```

Note: To use the built static assets at runtime, use [build.assets](/docs/files#build-assets).

### Example: Install a runtime dependency

```sh shuttle_setup_container.sh theme={null}
apt update
apt install -y ffmpeg
```