# `rust-musl-builder`: Docker container for easily building static Rust binaries

[![Docker Image](https://img.shields.io/docker/pulls/ekidd/rust-musl-builder.svg?maxAge=2592000)](https://hub.docker.com/r/ekidd/rust-musl-builder/)

Do you want to compile a completely static Rust binary with no external dependencies?  If so, try:

```sh
alias rust-musl-builder='docker run --rm -it -v "$(pwd)":/home/rust/src ekidd/rust-musl-builder'
rust-musl-builder cargo build --release
```

To target ARM hard float (Raspberry Pi):
```sh
rust-musl-builder cargo build --target=armv7-unknown-linux-gnueabihf --release
```

This command assumes that `$(pwd)` is readable and writable by uid 1000, gid 1000.  It will output binaries in `target/x86_64-unknown-linux-musl/release`.  At the moment, it doesn't attempt to cache libraries between builds, so this is best reserved for making final release builds.

## Deploying your Rust application

With a bit of luck, you should be able to just copy your application binary from `target/x86_64-unknown-linux-musl/release`, and install it directly on any reasonably modern x86_64 Linux machine.  In particular, you should be able make static release binaries using TravisCI and GitHub, or you can copy your Rust application into an [Alpine Linux container][]. See below for details!

## How it works

`rust-musl-builder` uses [musl-libc][], [musl-gcc][], and the new [rustup][] `target` support.  It includes static versions of several libraries:

- The standard `musl-libc` libraries.
- OpenSSL, which is needed by many Rust applications.
- `libpq`, which is needed for applications that use `diesel` with PostgreSQL. Note that this may be broken under Rust 1.21.0 and later (see https://github.com/emk/rust-musl-builder/issues/27).
- `libz`, which is needed by `libpq`.

You can also use the following libraries with a bit of setup:

- SQLite3 with
  `diesel`. See [examples/using-diesel](./examples/using-diesel/).

This library also sets up the environment variables needed to compile popular Rust crates using these libraries.

## Making OpenSSL work

If your application uses OpenSSL, you will also need to take a few extra steps to make sure that it can find OpenSSL's list of trusted certificates, which is stored in different locations on different Linux distributions. You can do this using [`openssl-probe`](https://crates.io/crates/openssl-probe) as follows:

```rust
extern crate openssl_probe;

fn main() {
    openssl_probe::init_ssl_cert_env_vars();
    //... your code
}
```

## Making Diesel work

In addition to setting up OpenSSL, you'll need to add the following lines to your `Cargo.toml`:

```toml
[dependencies]
# This is needed to make sure that Cargo statically links against
# `libssl`. This should happen automatically, but it doesn't.
openssl-sys = "0.9"

[patch.crates-io]
# This is needed to handle cross-compilation of libpq.
pq-sys = { git = 'https://github.com/golddranks/pq-sys' }
```

See [this PR](https://github.com/sgrif/pq-sys/pull/18) for a discussion of the issues involved in cross-compiling `diesel` and `diesel_codegen`.

## Making static releases with Travis CI and GitHub

These instructions are inspired by [rust-cross][].

First, read the [Travis CI: GitHub Releases Uploading][uploading] page, and run `travis setup releases` as instructed.  Then add the following lines to your existing `.travis.yml` file, replacing `myapp` with the name of your package:

```yaml
language: rust
sudo: required
os:
- linux
- osx
rust:
- stable
services:
- docker
before_deploy: "./build-release myapp ${TRAVIS_TAG}-${TRAVIS_OS_NAME}"
deploy:
  provider: releases
  api_key:
    secure: "..."
  file_glob: true
  file: "myapp-${TRAVIS_TAG}-${TRAVIS_OS_NAME}.*"
  skip_cleanup: true
  on:
    rust: stable
    tags: true
```

Next, copy [`build-release`](./examples/build-release) into your project and run `chmod +x build-release`.

Finally, add a `Dockerfile` to perform the actual build:

```rust
FROM ekidd/rust-musl-builder

# We need to add the source code to the image because `rust-musl-builder`
# assumes a UID of 1000, but TravisCI has switched to 2000.
ADD . ./
RUN sudo chown -R rust:rust .

CMD cargo build --release
```

When you push a new tag to your project, `build-release` will automatically build new Linux binaries using `rust-musl-builder`, and new Mac binaries with Cargo, and it will upload both to the GitHub releases page for your repository.

For a working example, see [faradayio/cage][cage].

[rust-cross]: https://github.com/japaric/rust-cross
[uploading]: https://docs.travis-ci.com/user/deployment/releases
[cage]: https://github.com/faradayio/cage

## Making tiny Docker images with Alpine Linux and Rust binaries

Docker now supports [multistage builds][multistage], which make it easy to build your Rust application with `rust-musl-builder` and deploy it using [Alpine Linux][]. For a working example, see [`examples/using-diesel/Dockerfile`](./examples/using-diesel/Dockerfile).

[multistage]: https://docs.docker.com/engine/userguide/eng-image/multistage-build/
[Alpine Linux]: https://alpinelinux.org/

## Adding more C libraries

If you're using Docker crates which require specific C libraries to be installed, you can create a `Dockerfile` based on this one, and use `musl-gcc` to compile the libraries you need.  For an example, see [`examples/adding-a-library/Dockerfile`](./examples/adding-a-library/Dockerfile). This usually involves a bit of experimentation for each new library, but it seems to work well for most simple, standalone libraries.

If you need an especially common library, please feel free to submit a pull request adding it to the main `Dockerfile`!  We'd like to support popular Rust crates out of the box.

## Development notes

After modifying the image, run `./test-image` to make sure that everything works.xs

## Other ways to build portable Rust binaries

If for some reason this image doesn't meet your needs, there's a variety of other people working on similar projects:

- [messense/rust-musl-cross](https://github.com/messense/rust-musl-cross) shows how to build binaries for many different architectures.
- [japaric/rust-cross](https://github.com/japaric/rust-cross) has extensive instructions on how to cross-compile Rust applications.
- [clux/muslrust](https://github.com/clux/muslrust) also supports libcurl.
- [golddranks/rust_musl_docker](https://github.com/golddranks/rust_musl_docker). Another Docker image.

## License

Either the [Apache 2.0 license](./LICENSE-APACHE.txt), or the
[MIT license](./LICENSE-MIT.txt).

[Alpine Linux container]: https://hub.docker.com/_/alpine/
[musl-libc]: http://www.musl-libc.org/
[musl-gcc]: http://www.musl-libc.org/how.html
[rustup]: https://www.rustup.rs/