Cross-Platform GitHub Action

This project provides a GitHub action for running GitHub Action workflows on multiple platforms. This includes platforms that GitHub Actions doesn't currently natively support.

Features

Some of the features that are supported include:

Multiple operating system with one single action
Multiple versions of each operating system
Allows to use default shell or Bash shell
Low boot overhead
Fast execution

Usage

Here's a sample workflow file which will setup a matrix resulting in four jobs. One which will run on FreeBSD 13.1, one which runs OpenBSD 7.2, one which runs NetBSD 9.2 and one which runs OpenBSD 7.2 on ARM64.

name: CI

on: [push]

jobs:
  test:
    runs-on: ${{ matrix.os.host }}
    strategy:
      matrix:
        os:
          - name: freebsd
            architecture: x86-64
            version: '13.1'
            host: macos-12

          - name: openbsd
            architecture: x86-64
            version: '7.2'
            host: macos-12

          - name: openbsd
            architecture: arm64
            version: '7.2'
            host: ubuntu-latest

          - name: netbsd
            architecture: x86-64
            version: '9.2'
            host: ubuntu-latest

    steps:
      - uses: actions/checkout@v2

      - name: Test on ${{ matrix.os.name }}
        uses: cross-platform-actions/action@v0.9.0
        env:
          MY_ENV1: MY_ENV1
          MY_ENV2: MY_ENV2
        with:
          environment_variables: MY_ENV1 MY_ENV2
          operating_system: ${{ matrix.os.name }}
          architecture: ${{ matrix.os.architecture }}
          version: ${{ matrix.os.version }}
          shell: bash
          run: |
            uname -a
            echo $SHELL
            pwd
            ls -lah
            whoami
            env | sort

Different platforms need to run on different runners, see the Runners section below.

Inputs

This section lists the available inputs for the action.

Input	Required	Default Value	Description
`run`	✓	✗	Runs command-line programs using the operating system's shell. This will be executed inside the virtual machine.
`operating_system`	✓	✗	The type of operating system to run the job on. See Supported Platforms.
`version`	✓	✗	The version of the operating system to use. See Supported Platforms.
`shell`	✗	`default`	The shell to use to execute the commands. Defaults to the default shell for the given operating system. Allowed values are: `default`, `sh` and `bash`
`environment_variables`	✗	`""`	A list of environment variables to forward to the virtual machine. The list should be separated with spaces.

All inputs are expected to be strings. It's important that especially the version is explicitly specified as a string, using single or double quotes. Otherwise YAML might interpet the value as a numeric value instead of a string. This might lead to some unexpected behavior. If the version is specified as version: 13.0, YAML will interpet 13.0 as a floating point number, drop the fraction part (because 13 and 13.0 are the same) and the GitHub action will only see 13 instead of 13.0. The solution is to explicitly state that a string is required by using quotes: version: '13.0'.

Supported Platforms

This sections lists the currently supported platforms by operating system. Each operating system will list which versions are supported.

OpenBSD (`openbsd`)

Version	x86-64	arm64
7.2	✓	✓
7.1	✓	✓
6.9	✓	✓
6.8	✓	✗

FreeBSD (`freebsd`)

Version	x86-64
13.1	✓
13.0	✓
12.4	✓
12.2	✓

NetBSD (`netbsd`)

Version	x86-64
9.2	✓

Runners

This section list the different combinations of platforms and on which runners they can run.

Runner	OpenBSD	FreeBSD	NetBSD
Linux	✓	✓	✓
macos-10.15, macos-11, macos-12	✓	✓	✗

Under the Hood

GitHub Actions currently only support the following platforms: macOS, Linux and Windows. To be able to run other platforms, this GitHub action runs the commands inside a virtual machine (VM). If the host platform is macOS the hypervisor can take advantage of nested virtualization.

The FreeBSD and OpenBSD VMs run on the xhyve hypervisor (on a macOS host), while the other platforms run on the QEMU hypervisor (on a Linux host). xhyve is built on top of Apple's Hypervisor framework. The Hypervisor framework allows to implement hypervisors with support for hardware acceleration without the need for kernel extensions. xhyve is a lightweight hypervisor that boots the guest operating systems quickly and requires no dependencies outside of what's provided by the system. QEMU is a more general purpose hypervisor that runs on most host platforms and supports most guest systems. It's a bit slower than xhyve because it's general purpose and it cannot use nested virtualization on the Linux hosts provided by GitHub.

The VM images running inside the hypervisor are built using Packer. It's a tool for automatically creating VM images, installing the guest operating system and doing any final provisioning.

The GitHub action uses SSH to communicate and execute commands inside the VM. It uses rsync to share files between the guest VM and the host. xhyve does not have any native support for sharing files. To authenticate the SSH connection a unique key pair is used. This pair is generated each time the action is run. The public key is added to the VM image and the private key is stored on the host. Since xhyve does not support file sharing, a secondar hard drive, which is backed by a file, is created. The public key is stored on this hard drive, which is then mounted by the VM. At boot time, the secondary hard drive will be identified and the public key will be copied to the appropriate location.

To reduce the time it takes for the GitHub action to start executing the commands specified by the user, it aims to boot the guest operating systems as fast as possible. This is achieved in a couple of ways:

By downloading resources, like the hypervisor and a few other tools, instead of installing them through a package manager
No compression is used for the resources that are downloaded. The size is small enough anyway and it's faster to download the uncompressed data than it is to download compressed data and then uncompress it.
It leverages async/await to perform tasks asynchronously. Like downloading the VM image and other resources at the same time
It performs as much as possible of the setup ahead of time when the VM image is provisioned

Local Development

Prerequisites

Instructions

Install the above prerequisites

Clone the repository by running:

git clone https://github.com/cross-platform-actions/action

Navigate to the newly cloned repository: cd action
Install the dependencies by running: npm install
Run any of the below npm commands

npm Commands

The following npm commands are available:

build - Build the GitHub action
format - Reformat the code
lint - Lint the code
package - Package the GitHub action for distribution and end to end testing
test - Run unit tests
all - Will run all of the above commands

Running End to End Tests

The end to end tests can be run locally by running it through Act. By default, resources and VM images will be downloaded from github.com. By running a local HTTP server it's possible to point the GitHub action to local resources.

Prerequisites

Docker
Act

Instructions

Install the above prerequisites
Copy test/workflows/ci.yml.example to test/workflows/ci.yml
Make any changes you like to test/workflows/ci.yml, this is file ignored by Git
Build the GitHub action by running: npm run build
Package the GitHub action by running: npm run package
Run the GitHub action by running: act --privileged -W test/workflows

Providing Resources Locally

The GitHub action includes a development dependency on a HTTP server. The test/http directory contains a skeleton of a directory structure which matches the URLs that the GitHub action uses to download resources. All files within the test/http are ignore by Git.

Add resources as necessary to the test/http directory
In one shell, run the following command to start the HTTP server:
```
./node_modules/http-server/bin/http-server test/http -a 127.0.0.1
```
The -a flag configures the HTTP server to only listen for incoming connections from localhost, no external computers will be able to connect.
In another shell, run the GitHub action by running:
```
act --privileged -W test/workflows --env CPA_RESOURCE_URL=<url>
```
Where <url> is the URL inside Docker that points to localhost of the host machine, for macOS, this is http://host.docker.internal:8080. By default, the HTTP server is listening on port 8080.

abernard/action

Cross-Platform GitHub Action

Features

Usage

Inputs

Supported Platforms

OpenBSD (openbsd)

FreeBSD (freebsd)

NetBSD (netbsd)

Runners

Under the Hood

Local Development

Prerequisites

Instructions

npm Commands

Running End to End Tests

Prerequisites

Instructions

Providing Resources Locally

OpenBSD (`openbsd`)

FreeBSD (`freebsd`)

NetBSD (`netbsd`)