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https://github.com/emk/heroku-buildpack-rust

A buildpack for Rust applications on Heroku, with full support for Rustup, cargo and build caching.
https://github.com/emk/heroku-buildpack-rust

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A buildpack for Rust applications on Heroku, with full support for Rustup, cargo and build caching.

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# Heroku buildpack for Rust



[![Build Status](https://travis-ci.org/emk/heroku-buildpack-rust.svg?branch=master)](https://travis-ci.org/emk/heroku-buildpack-rust)



This is a Heroku buildpack for Rust with support for [cargo][] and [rustup][].  Features include:



- Caching of builds between deployments.

- Automatic updates to the latest stable Rust by default.

- Optional pinning of Rust to a specific version.

- Support for `export` so that other buildpacks can access the Rust toolchain.

- Support for compiling Rust-based extensions for projects written in other languages.



[fode]: https://github.com/ericfode/heroku-buildpack-rust

[cargo]: http://crates.io/

[rustup]: https://www.rustup.rs/



## Example projects



Here are several example projects:



- [rust-buildpack-example-actix][] uses the popular [Actix][] framework, and runs on stable Rust.

- [rust-buildpack-example-rocket][] uses the innovative [Rocket][] framework, which currently requires nightly Rust.



[rust-buildpack-example-actix]: https://github.com/emk/rust-buildpack-example-actix

[Actix]: https://actix.rs/

[rust-buildpack-example-rocket]: https://github.com/emk/rust-buildpack-example-rocket

[Rocket]: https://rocket.rs/



## Using this buildpack



To deploy an application to Heroku, we recommend installing the [Heroku CLI][].



If you're creating a new Heroku application, `cd` to the directory containing your code, and run:



```sh

heroku create --buildpack emk/rust

```



This will only work if your application has a `Cargo.toml` and uses `git`. If you want to set a particular name for application, see `heroku create --help` first.



To use this as the buildpack for an existing application, run:



```sh

heroku buildpacks:set emk/rust

```



You will also need to create a `Procfile` pointing to the release version of your application, and commit it to `git`:



```Procfile

web: ./target/release/hello

```



...where `hello` is the name of your binary.



To deploy your application, run:



```sh

git push heroku master

```



### Running Diesel migrations during the release phase



This will install the diesel CLI at build time and make it available in your dyno. Migrations will run whenever a new version of your app is released. Add the following line to your `RustConfig`



```sh

RUST_INSTALL_DIESEL=1

```



and this one to your `Procfile`



```Procfile

release: ./target/release/diesel migration run

```



[Heroku CLI]: https://devcenter.heroku.com/articles/heroku-command-line



## Specifying which version of Rust to use



By default, your application will be built using the latest stable Rust. Normally, this is pretty safe: New stable Rust releases have excellent backwards compatibility.



But you may wish to use `nightly` Rust or to lock your Rust version to a known-good configuration for more reproducible builds. To specify a specific version of the toolchain, use a [`rust-toolchain`](https://github.com/rust-lang-nursery/rustup.rs#the-toolchain-file) file in the format rustup uses.



Note: if you previously specified a `VERSION` variable in `RustConfig`, that will continue to work, and will override a `rust-toolchain` file.



## Combining with other buildpacks



If you have a project which combines both Rust and another programming language, you can insert this buildpack before your existing one as follows:



```sh

heroku buildpacks:add --index 1 emk/rust

```



If you have a valid `Cargo.toml` in your project, this is all you need to do. The Rust buildpack will run first, and your existing buildpack will run second.



But if you only need Rust to build a particular Ruby gem, and you have no top-level `Cargo.toml` file, you'll need to let the buildpack know to skip the build stage.  You can do this by adding the following line to `RustConfig`:



```sh

RUST_SKIP_BUILD=1

```



## Customizing build flags



If you want to change the cargo build command, you can set the `RUST_CARGO_BUILD_FLAGS` variable inside the `RustConfig` file.



```sh

RUST_CARGO_BUILD_FLAGS="--release -p some_package --bin some_exe --bin some_bin_2"

```



The default value of `RUST_CARGO_BUILD_FLAGS` is `--release`.

If the variable is not set in `RustConfig`, the default value will be used to build the project.



## Using the edge version of the buildpack



The `emk/rust` buildpack from the [Heroku Registry](https://devcenter.heroku.com/articles/buildpack-registry) contains the latest stable version of the buildpack. If you'd like to use the latest buildpack code from this Github repository, you can set your buildpack to the Github URL:



```sh

heroku buildpacks:set https://github.com/emk/heroku-buildpack-rust

```



## Development notes



If you need to tweak this buildpack, the following information may help.



### Testing with Docker



To test changes to the buildpack using the included `docker-compose-test.yml`, run:



```sh

./test_buildpack

```



Then make sure there are no Rust-related *.so files getting linked:



```sh

ldd heroku-rust-cargo-hello/target/release/hello

```



This uses the Docker image `heroku/cedar`, which allows us to test in an official Cedar-like environment.



We also run this test automatically on Travis CI.