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

• Source on GitHub
• Changelog

UPDATED: Major updates in this release which may break some builds. See the CHANGELOG for details. If these updates break your build, you can update your Dockerfile to use FROM ekidd/rust-musl-builder:1.48.0 to revert to the previous version.

What is this?

This image allows you to build static Rust binaries using diesel, sqlx or openssl. These images can be distributed as single executable files with no dependencies, and they should work on any modern Linux system.

To try it, run:

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

This command assumes that $(pwd) is readable and writable by uid 1000, gid 1000. At the moment, it doesn't attempt to cache libraries between builds, so this is best reserved for making final release builds.

For a more realistic example, see the Dockerfiles for examples/using-diesel and examples/using-sqlx.

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!

Available tags

In general, we provide the following tagged Docker images:

• latest, stable: Current stable Rust, now with OpenSSL 1.1. We try to update this fairly rapidly after every new stable release, and after most point releases.
• X.Y.Z: Specific versions of stable Rust.
• beta: This usually gets updated every six weeks alongside the stable release. It will usually not be updated for beta bugfix releases.
• nightly-YYYY-MM-DD: Specific nightly releases. These should almost always support clippy, rls and rustfmt, as verified using rustup components history. If you need a specific date for compatibility with tokio or another popular library using unstable Rust, please file an issue.

At a minimum, each of these images should be able to compile examples/using-diesel and examples/using-sqlx.

Caching builds

You may be able to speed up build performance by adding the following -v commands to the rust-musl-builder alias:

-v cargo-git:/home/rust/.cargo/git
-v cargo-registry:/home/rust/.cargo/registry
-v target:/home/rust/src/target

You will also need to fix the permissions on the mounted volumes:

rust-musl-builder sudo chown -R rust:rust \
  /home/rust/.cargo/git /home/rust/.cargo/registry /home/rust/src/target

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.
• libz, which is needed by libpq.
• SQLite3. See examples/using-diesel.

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

Extras

This image also supports the following extra goodies:

• Basic compilation for armv7 using musl-libc. Not all libraries are supported at the moment, however.
• mdbook and mdbook-graphviz for building searchable HTML documentation from Markdown files. Build manuals to use alongside your cargo doc output!
• cargo about to collect licenses for your dependencies.
• cargo deb to build Debian packages
• cargo deny to check your Rust project for known security issues.

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 as follows:

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:

[dependencies]
diesel = { version = "1", features = ["postgres", "sqlite"] }

# Needed for sqlite.
libsqlite3-sys = { version = "*", features = ["bundled"] }

# Needed for Postgres.
openssl = "*"

For PostgreSQL, you'll also need to include diesel and openssl in your main.rs in the following order (in order to avoid linker errors):

extern crate openssl;
#[macro_use]
extern crate diesel;

If this doesn't work, you might be able to fix it by reversing the order. See this PR for a discussion of the latest issues involved in linking to diesel, pq-sys and openssl-sys.

Making static releases with Travis CI and GitHub

These instructions are inspired by rust-cross.

First, read the Travis CI: GitHub Releases 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:

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 into your project and run chmod +x build-release.

Finally, add a Dockerfile to perform the actual build:

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 --chown=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.

Making tiny Docker images with Alpine Linux and Rust binaries

Docker now supports multistage builds, 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.

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. 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.

ARM support (experimental)

To target ARM hard float (Raspberry Pi):

rust-musl-builder cargo build --target=armv7-unknown-linux-musleabihf --release

Binaries will be written to target/$TARGET_ARCHITECTURE/release. By default it targets x86_64-unknown-linux-musl unless specified with --target.

This is missing many of the libraries used by the x86_64 build, and it should probably be split out of the base image and given its own tags.

Development notes

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

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 shows how to build binaries for many different architectures.
• japaric/rust-cross has extensive instructions on how to cross-compile Rust applications.
• clux/muslrust also supports libcurl.
• golddranks/rust_musl_docker. Another Docker image.

License

Either the Apache 2.0 license, or the MIT license.