containerization-framework

Rust bindings for Apple's Containerization framework: Linux containers.

The Rust API mirrors Containerization's Swift API as much as possible. Modules are named after the Swift modules, types after the Swift types, and methods after their Swift methods, except for using snake case. A Swift type nested in another, like LinuxContainer.Configuration, is found in a module named after its parent: linux_container::Configuration. Types are grouped into modules of related types, such as containerization::container and containerization_oci::image, so a path reads containerization::container::linux_container::Configuration.

use containerization_framework as cfw;
use cfw::containerization as cz;
use cfw::containerization_extras as cz_extras;

let store = cz::image::ImageStore::new("/Users/me/.cache/containers".as_ref())?;
let kernel = cz::vm::Kernel::new("/Users/me/.cache/vmlinux", cz::vm::SystemPlatform::LINUX_ARM);
let mut manager = cz::container::ContainerManager::with_initfs_reference(
    &kernel,
    "ghcr.io/apple/containerization/vminit:0.49.0",
    &store,
    Default::default(),
)?;

let image = store.get("docker.io/library/alpine:3", true)?;
let address = cz_extras::address::CIDRv4::parse("192.168.64.7/24")?;
let gateway = cz_extras::address::IPv4Address::parse("192.168.64.1")?;
let options = cz::container::container_manager::CreateOptions { networking: false, ..Default::default() };
let container = manager.create("example", &image, options, move |config| {
    config.process.arguments = vec!["/bin/sleep".into(), "infinity".into()];
    config.interfaces = vec![cz::network::Interface::Nat(cz::network::NATInterface::new(address, Some(gateway)))];
    config.dns = Some(cz::network::DNS { nameservers: vec!["192.168.64.1".into()], ..Default::default() });
    Ok(())
})?;
container.create()?;
container.start()?;

let process = container.exec("hello", cz::process::LinuxProcessConfiguration::new(&["/bin/echo", "hello"]))?;
process.start()?;
let status = process.wait(None)?;
process.delete()?;

container.stop()?;
manager.delete("example")?;

Swift's async methods block until they finish, and errors they throw are returned as cfw::Error. A container belongs to the process that created it, and stops when that process exits.

Requirements

• macOS 26 on Apple silicon, and Xcode 26 to build.
• Network on a first build: the build script compiles the bundled Swift package, which resolves Containerization and its dependencies through SwiftPM. Versions are pinned by the Package.resolved that ships with this crate.

On other platforms this crate compiles, so a cross-platform workspace builds, but every call that would reach Swift returns Error::Unavailable. Values built purely in Rust, such as IPv4Address::new or Descriptor::new, work as usual.

Codesigning

A binary using this crate must carry the com.apple.security.virtualization entitlement. Without it Virtualization.framework refuses to start a VM, and LinuxContainer::create fails.

A containerization.entitlements file ships with this crate; binaries compiled against containerization-framework should pass it, or a copy of it, to codesign after compilation.

cargo build --release
codesign --force --sign - --entitlements containerization.entitlements \
  target/release/your-binary

Signing ad hoc (--sign -) satisfies the entitlement but gives the binary a new code identity on every rebuild, so anything keyed to that identity — Keychain access, for one — prompts again. Sign with a development identity to keep it stable.

A rebuild drops the signature, so this runs after every build.

Linking

The Swift runtime this links against is dynamic and referenced as @rpath/libswift_Concurrency.dylib, which dyld resolves against /usr/lib/swift in macOS. Anything that links this crate — a binary of yours, and the test binaries of any crate of yours that links it — needs that rpath, or it links and then dies in dyld at launch.

A build script's link arguments reach only its package's targets, so the rpath belongs in .cargo/config.toml, where a rustflag covers every kind of target:

[target.'cfg(target_os = "macos")']
rustflags = ["-C", "link-arg=-Wl,-rpath,/usr/lib/swift"]

Shape

• containerization, in five groups. image: ImageStore, Image, image::Description, InitImage, KernelImage, EXT4Unpacker. vm: Kernel, SystemPlatform, VMConfiguration, VMResources, BootLog, VZVirtualMachineManager, VZVirtualMachineInstance, Vminitd, VsockListener. network: VmnetNetwork, NATInterface, Interface, DNS, Hosts. container: ContainerManager, LinuxContainer, LinuxPod, Mount, and the configuration types they take (linux_container::Configuration, ...). process: LinuxProcess, LinuxProcessConfiguration, Signal, LinuxCapabilities, ExitStatus. Their defaults match Containerization's.
• containerization_oci, in four groups. content: LocalContentStore, Content, ContentWriter. image: Descriptor, Platform, Reference, Manifest. client: RegistryClient, Authentication, KeychainHelper. runtime: Spec and the types it holds, Bundle, State, User.
• containerization_archive: ArchiveReader, ArchiveWriter, WriteEntry, and the formats and filters they take.
• containerization_error: the Code that a thrown ContainerizationError carries, which Error::is_code checks.
• containerization_ext4: ext4::Formatter, ext4::EXT4Reader, ext4::SuperBlock, ext4::Inode, ext4::JournalConfig, FileTimestamps.
• containerization_extras: in address, IPv4Address, IPv6Address, IPAddress, Prefix, CIDRv4, CIDRv6, CIDR and MACAddress; at the root, InterfaceAddress, LinkRoute, DefaultRoute, ProgressEvent and ProgressHandler; and proxy_utils.
• containerization_io: ReadStream.
• containerization_os: Terminal, sysctl, file, keychain::KeychainQuery, and in linux, CapabilityName, CapabilitySet and binfmt.

A few things work differently because Rust can't express them the way Swift does:

• Rust has no default arguments, so ContainerManager.create's optional arguments are fields of container::container_manager::CreateOptions. Its Default uses the same values as Swift. An initializer's options struct is named after its type, such as ContainerManagerOptions, and a method's is named after the Rust method, such as CreateWithRootfsOptions.
• Rust has no overloading either. Where Swift overloads a name, the second Rust method adds a suffix naming the argument that tells them apart: ContainerManager.create(_:image:rootfs:...) is create_with_rootfs, and ImageStore(path:contentStore:) is ImageStore::with_content_store. Where the overloads differ only in taking a closure, as with LinuxContainer.exec, the one taking a closure ends in _with.
• Where Swift takes a ReaderStream or Writer for a process's stdin, stdout and stderr, Rust takes a file descriptor. Swift uses a duplicate of it, so you keep yours open and close it yourself.
• ContainerManager.create takes a Rust closure. It receives the configuration the manager has prepared and runs on a Swift thread, so it must be Send + 'static. So must LocalContentStore.ingest's body and a ProgressHandler, and a ProgressHandler must also be Sync.
• Swift's configuration closures can throw, so Rust's return Result<(), Error>. To throw, return Err(Error::failed(...)). An error the closure returns is the one the call returns.
• Content.decode() is generic over Swift's Decodable, which Rust can't call. Read Content::data and decode the bytes yourself.
• Swift computes everything about an address, from parsing it to its description and isLoopback. Each of those calls Swift and returns a Result, which is why addresses have a description method rather than Display. Their PartialOrd and Platform's PartialEq call Swift's operators too, so off macOS, comparing them panics.
• Where Swift's initializer checks or changes a value, as with Prefix, CIDRv4, CIDRv6 and MACAddress, only Swift makes one, so their fields are read through getters.

OCI runtimes

An OCI runtime, and with it a seccomp profile, can be configured. Swift refuses a seccomp profile without an OCI runtime path, and the runtime has to be in the init image. The init image Apple publishes has no runc, so such a container fails to start unless you build an init image with one.

Versioning

The init image's vminitd must match the Containerization release this crate builds against (0.49.0, in swift/Package.swift): they share a protocol, and a mismatch fails at runtime rather than at build time. As in Containerization, the caller chooses the kernel and the init image.

Testing

cargo nextest run runs the unit tests. They also check Rust's copies of Swift values, such as raw values, defaults and struct layouts, against Swift.

The suites in tests/ call into the real framework, so they sit behind the integration feature and run through bin/dev/test-integration. Some only ask Swift for values, while others boot real containers and VMs. The script signs each test binary with containerization.entitlements first, because the entitlement is checked against the calling process. Run the suites only through the script: a test binary that cargo rebuilds after the script signed it has no entitlement, and its VMs fail to start.

Those tests share an image store at ~/.cache/containerization-framework-tests, which is kept between runs. Before the tests that boot a VM, nextest runs bin/dev/prepare-integration as a setup script, which downloads the kernel into the store. The tests then pull the init image and alpine:3 themselves, and the registry tests talk to Docker Hub. A first run therefore needs the network, and later runs reuse the store. The store's directory can be deleted at any time.

Two tests open Containerization's default image store, and in doing so create ~/Library/Application Support/com.apple.containerization if it is missing. The tests that need a vmnet network pass without checking anything on a host whose process lacks the vmnet entitlement, and say so in their output.

License

MIT. Containerization itself is Apache-2.0 and is fetched at build time, not vendored here.