Euan Harris
511dd59e19
swift-nio's public export of NIOFileSystem was removed in 2.86.1: https://github.com/apple/swift-nio/pull/3370 NIOFileSystem was not yet supposed to be public, but _NIOFileSystem depended on it as a public import. This made it possible for `containerization` to see the `NIOFileSystem` package by accident. Replacing the use of `NIOFileSystem` by `_NIOFileSystem`, as used elsewhere, fixes the problem. ## Why does CI currently pass? The change in `swift-nio` does not currently cause `containerization`'s CI to fail because `Package.resolved` pins `swift-nio` to 2.83.0, before the change was made. New versions of upstream dependencies will not be tested until `Package.resolved` is explicitly updated. When containerization is built as a dependency of a end-user project, its `Package.resolved` file is ignored. Instead, the dependency constraints from containerization's Package.swift file are combined with those of the project and any other library dependencies, so SwiftPM or Xcode can find a set of mutually compatible packages. This can lead to new versions of containerization's upstream dependencies being used, even though those versions have never been tested in CI. The build failure can be demonstrated by creating a new package which depends on `containerization` but does not constrain package versions: ``` % swift package init --type executable Creating executable package: test Creating Package.swift Creating Sources Creating Sources/test/test.swift % cat > Package.swift <<EOF heredoc> // swift-tools-version: 6.2 // The swift-tools-version declares the minimum version of Swift required to build this package. import PackageDescription let package = Package( name: "test", platforms: [ .macOS(.v26), ], dependencies: [ .package(url: "https://github.com/apple/containerization", from: "0.7.2"), ], targets: [ // Targets are the basic building blocks of a package, defining a module or a test suite. // Targets can depend on other targets in this package and products from dependencies. .executableTarget( name: "test", dependencies: [ .product(name: "Containerization", package: "containerization"), ] ), ] ) EOF % swift build ... /private/tmp/test/.build/checkouts/containerization/Sources/ContainerizationOCI/Client/RegistryClient+Fetch.swift:25:8: error: no such module 'NIOFileSystem' 23 | 24 | #if os(macOS) 25 | import NIOFileSystem | `- error: no such module 'NIOFileSystem' 26 | #endif 27 | ```
Containerization
The Containerization package allows applications to use Linux containers. Containerization is written in Swift and uses Virtualization.framework on Apple silicon.
Looking for command line binaries for running containers?
They are available in the dedicated apple/container repository.
Containerization provides APIs to:
- Manage OCI images.
- Interact with remote registries.
- Create and populate ext4 file systems.
- Interact with the Netlink socket family.
- Create an optimized Linux kernel for fast boot times.
- Spawn lightweight virtual machines and manage the runtime environment.
- Spawn and interact with containerized processes.
- Use Rosetta 2 for running linux/amd64 containers on Apple silicon.
Please view the API documentation for information on the Swift packages that Containerization provides.
Design
Containerization executes each Linux container inside of its own lightweight virtual machine. Clients can create dedicated IP addresses for every container to remove the need for individual port forwarding. Containers achieve sub-second start times using an optimized Linux kernel configuration and a minimal root filesystem with a lightweight init system.
vminitd is a small init system, which is a subproject within Containerization.
vminitd is spawned as the initial process inside of the virtual machine and provides a GRPC API over vsock.
The API allows the runtime environment to be configured and containerized processes to be launched.
vminitd provides I/O, signals, and events to the calling process when a process is run.
Requirements
To build the Containerization package, you need:
- Mac with Apple silicon
- macOS 26 beta
- Xcode 26 beta
Older versions of macOS are not supported.
Example Usage
For examples of how to use some of the libraries surface, the cctl executable is a good start. This app is a useful playground for exploring the API. It contains commands that exercise some of the core functionality of the various products, such as:
- Manipulating OCI images
- Logging in to container registries
- Creating root filesystem blocks
- Running simple Linux containers
Linux kernel
A Linux kernel is required for spawning lightweight virtual machines on macOS. Containerization provides an optimized kernel configuration located in the kernel directory.
This directory includes a containerized build environment to easily compile a kernel for use with Containerization.
The kernel configuration is a minimal set of features to support fast start times and a light weight environment.
While this configuration will work for the majority of workloads we understand that some will need extra features. To solve this Containerization provides first class APIs to use different kernel configurations and versions on a per container basis. This enables containers to be developed and validated across different kernel versions.
See the README in the kernel directory for instructions on how to compile the optimized kernel.
Kernel Support
Containerization allows user provided kernels but tests functionality starting with kernel version 6.14.9.
Pre-built Kernel
If you wish to consume a pre-built kernel, make sure it has VIRTIO drivers compiled into the kernel (not merely as modules).
The Kata Containers project provides a Linux kernel that is optimized for containers, with all required configuration options enabled. The releases page contains downloadable artifacts, and the image itself (vmlinux.container) can be found in the /opt/kata/share/kata-containers/ directory.
Prepare to build package
Install the recommended version of Xcode.
Set the active developer directory to the installed Xcode (replace <PATH_TO_XCODE>):
sudo xcode-select -s <PATH_TO_XCODE>
Install Swiftly, Swift, and Static Linux SDK:
make cross-prep
If you use a custom terminal application, you may need to move this command from .zprofile to .zshrc (replace <USERNAME>):
# Added by swiftly
. "/Users/<USERNAME>/.swiftly/env.sh"
Restart the terminal application. Ensure this command returns /Users/<USERNAME>/.swiftly/bin/swift (replace <USERNAME>):
which swift
If you've installed or used a Static Linux SDK previously, you may need to remove older SDK versions from the system (replace <SDK-ID>):
swift sdk list
swift sdk remove <SDK-ID>
Build the package
Build Containerization from sources:
make all
Test the package
After building, run basic and integration tests:
make test integration
A kernel is required to run integration tests.
If you do not have a kernel locally for use a default kernel can be fetched using the make fetch-default-kernel target.
Fetching the default kernel only needs to happen after an initial build or after a make clean.
make fetch-default-kernel
make all test integration
Protobufs
Containerization depends on specific versions of grpc-swift and swift-protobuf. You can install them and re-generate RPC interfaces with:
make protos
Documentation
Generate the API documentation for local viewing with:
make docs
make serve-docs
Preview the documentation by running in another terminal:
open http://localhost:8000/containerization/documentation/
Contributing
Contributions to Containerization are welcomed and encouraged. Please see CONTRIBUTING.md for more information.
Project Status
Version 0.1.0 is the first official release of Containerization. Earlier versions have no source stability guarantees.
Because the Containerization library is under active development, source stability is only guaranteed within minor versions (for example, between 0.1.1 and 0.1.2). If you don't want potentially source-breaking package updates, you can specify your package dependency using .upToNextMinorVersion(from: "0.1.0") instead.
Future minor versions of the package may introduce changes to these rules as needed.