Heroku buildpack: swift

This is a Heroku buildpack for Swift apps that are powered by the Swift Package Manager.

Example usage:

$ ls
Procfile Package.swift Sources

$ heroku create --buildpack vapor/vapor

$ git push heroku main
remote: -----> Swift app detected
remote: -----> Using Swift 5.10 (default)
remote: -----> Using built-in clang (Swift 5.10)
remote: -----> Installing swiftenv
remote: -----> Installing Swift 5.10
...

You can also add it to upcoming builds of an existing application:

$ heroku buildpacks:set vapor/vapor

The buildpack will detect your app as Swift if it has a Package.swift file in the root.

Using the Procfile, you can set the process to run for your web server. Any binaries built from your Swift source using swift package manager will be placed in your $PATH.

Example Procfile for Vapor 3 and 4 apps:

web: Run serve --env production --hostname 0.0.0.0 --port $PORT

Example Procfile for Vapor 2 apps:

web: Run --env=production --port=$PORT

The buildpack defaults to Swift 5.10 and will be updated when new Swift versions are released.

If you need to use a specific version of the Swift toolchain, including older versions – for example Swift 4.2.x to retain compatibility with Swift 3 projects, or a previous version as you run into issues with the latest – you can pin any version number using a file called .swift-version in the root of the project folder, or by setting a SWIFT_VERSION configuration variable on Heroku, then deploying again.

$ echo '5.9.2' > .swift-version
$ git add .swift-version
$ git commit -m "Pin Swift version to 5.9.2"
$ git push heroku main

Or:

$ heroku config:set SWIFT_VERSION=5.9.2
$ git commit -m "Pin Swift version to 5.9.2" --allow-empty
$ git push heroku main

The version format used file is compatible with swiftenv.

By default, the buildpack will use the release build configuration to enable compiler optimizations. If you are experiencing mysterious crashes, you can try disabling them by setting the SWIFT_BUILD_CONFIGURATION config variable to debug, then redeploying.

$ heroku config:set SWIFT_BUILD_CONFIGURATION=debug
$ git commit -m "Change to debug configuration on Heroku" --allow-empty
$ git push heroku master
...
remote: -----> Building package (debug configuration)
...

If you want to pass extra flags to the swift build command, you can do so by setting the SWIFT_BUILD_FLAGS config variable. The most common use of this feature is to enable test discovery for older versions of Swift.

Swift 5.4+ runs test discovery by default, making this section finally obsolete.

Previously, projects with a test target needed either a LinuxMain.swift file, or a build flag that enables test discovery, to build successfully on Linux. Lacking them, the build would fail with an error message like below:

remote: error: missing LinuxMain.swift file in the Tests directory
remote:  !     Push rejected, failed to compile Swift app.
remote: 
remote:  !     Push failed

The easy and low-maintenance solution was passing the --enable-test-discovery build flag via Heroku configuration and attempting to deploy again.

The following example demonstrates this:

$ heroku config:set SWIFT_BUILD_FLAGS="--enable-test-discovery"
$ git commit -m "Enable test discovery on Heroku" --allow-empty
$ git push heroku master

Note that the empty commit is only required if uncommitted files and the previous deployment was successful.

You can place custom scripts to be run before and after compiling and installing your Swift source code inside the following files in your repository:

• bin/pre_compile
• bin/post_compile
• bin/pre_install
• bin/post_install

This is useful if you need to customize the final image.

The buildpack passes three arguments to the scripts: the BUILD_DIR, CACHE_DIR and ENV_DIR paths that Heroku provided for the build. See the Buildpack API documentation for details.

For larger projects with private dependencies, using heroku-buildpack-github-netrc is a solid solution – as long as the dependencies are on GitHub.

The same idea – using .netrc to pass in credentials – works for GitLab and other providers just as well.

The following pre_compile script creates a .netrc file from configuration variables. Save the script as bin/pre_compile in the root of your project.

# Load private git credentials from the app configuration
GIT_PRIVATE_DOMAIN=`cat $ENV_DIR/GIT_PRIVATE_DOMAIN | tr -d '[[:space:]]'`
GIT_PRIVATE_USER=`cat $ENV_DIR/GIT_PRIVATE_USER | tr -d '[[:space:]]'`
GIT_PRIVATE_PASSWORD=`cat $ENV_DIR/GIT_PRIVATE_PASSWORD | tr -d '[[:space:]]'`

# Create .netrc file with credentials
echo "machine $GIT_PRIVATE_DOMAIN" >> "$HOME/.netrc"
echo "login $GIT_PRIVATE_USER" >> "$HOME/.netrc"
echo "password $GIT_PRIVATE_PASSWORD" >> "$HOME/.netrc"

# Create cleanup script so the dyno does not see these values at runtime
mkdir -p "$BUILD_DIR/.profile.d"
echo "unset GIT_PRIVATE_DOMAIN" >> "$BUILD_DIR/.profile.d/netrc.sh"
echo "unset GIT_PRIVATE_USER" >> "$BUILD_DIR/.profile.d/netrc.sh"
echo "unset GIT_PRIVATE_PASSWORD" >> "$BUILD_DIR/.profile.d/netrc.sh"

Then define the GIT_PRIVATE_DOMAIN, GIT_PRIVATE_USER and GIT_PRIVATE_PASSWORD configuration variables on the Heroku dashboard, or via the heroku config:set command.

See the following example for the latter:

heroku config:set GIT_PRIVATE_DOMAIN=gitlab.com \
  GIT_PRIVATE_USER=user@organization.com \
  GIT_PRIVATE_PASSWORD=As1D2f34

Then commit and deploy the project again.

The vapor/vapor buildpack from the Heroku Buildpack Registry represents the latest stable version of the buildpack. If you'd like to use the source code from this Github repository, you can set your buildpack to the Github URL:

$ heroku buildpacks:set https://github.com/vapor-community/heroku-buildpack.git