The functional innards of Docker for Mac and Windows

Most developers use a Mac or Windows host to develop Docker Linux containers. This normally requires the installation of a Linux virtual machine as well as a complicated setup that includes a local networked filesystem for sharing data between the host and the Linux container, including UID mapping and case sensitivity, with inotify often being unreliable into the container; replicating Linux networking configuration locally to reflect the structure of the deployed microservices on the local laptop; and maintaining a separate Linux virtual machine and hypervisor such as VirtualBox, leading to heavyweight resource usage on a developer laptop.

I describe the architecture of Docker for Mac and Windows, which ships a lightweight hypervisor and user-level networking and filesystem functionality to greatly improve the developer experience with Docker on popular platforms.

Transcript

1. The functional innards of
 Docker for Mac and Windows Anil Madhavapeddy, @avsm Docker Inc, @docker Jane Street London, Functional Meetup, June 2016
 with thanks to the Docker for Mac and Windows teams for extensive contributions.
2. Transforming the Development Landscape 2 Loosely Coupled Many Small 
 Servers/Devices ~2000 Today Monolithic Big Iron Change Slowly Rapidly Updated
4. • All the Linux tools collected in one installer: • Bundle includes a full VirtualBox installation • Boot2Docker Virtual Machine • The Kitematic UI controlled these pieces. • A relatively loose collection of components: • Installation and lack of integrated updates caused numerous user issues. • Performance not ideal due to the layering, especially for file sharing. • Yet most Docker users use a Mac or Windows host as their development environment. Docker Toolbox
5. • Easy drag and drop installation, and autoupdates to get latest Docker. • Secure, sandboxed virtualisation architecture without elevated privileges. • Native networking support, with VPN and network sharing compatibility. • File sharing between container and host: uid mapping, inotify events, etc. Docker for Mac Aiming for a native OSX experience that works with existing developer workflows. Sign up at beta.docker.com
7. Virtualisation
8. • Uses the new HyperKit framework, which is in turn based on xHyve and FreeBSD's bHyve. • Sandbox friendly: processes largely run as non- root, with privileges of the local user. Virtualisation
9. • Uses the new HyperKit framework, which is in turn based on xHyve and FreeBSD's bHyve. • Sandbox friendly: processes largely run as non- root, with privileges of the local user. Virtualisation OSX Kernel Hypervisor. framework Hardware virt: VMX, nested paging
10. • Uses the new HyperKit framework, which is in turn based on xHyve and FreeBSD's bHyve. • Sandbox friendly: processes largely run as non- root, with privileges of the local user. Virtualisation OSX Kernel Userspace Hypervisor. framework User Process Thread/vCPU Traps on I/O pages Manages ACPI, PCI devices Hardware virt: VMX, nested paging
11. • Uses the new HyperKit framework, which is in turn based on xHyve and FreeBSD's bHyve. • Sandbox friendly: processes largely run as non- root, with privileges of the local user. Virtualisation OSX Kernel Userspace Hypervisor. framework User Process Hardware virt: VMX, nested paging Process Linux Kernel VirtIO IPC VirtIO Block VirtIO Net Alpine Linux Userspace Latest Docker preconfigured QCow2 VPNKit Logs redirected to OSX host
12. • Uses the new HyperKit framework, which is in turn based on xHyve and FreeBSD's bHyve. • Embeds Linux: includes an embedded lightweight Alpine Linux distribution optimised for fast boot and stateless operation for containers. Virtualisation $ docker info Containers: 358 Running: 13 Paused: 0 Stopped: 345 Images: 485 Server Version: 1.11.1 Storage Driver: aufs Root Dir: /var/lib/docker/aufs Backing Filesystem: extfs Dirperm1 Supported: true Logging Driver: json-file Cgroup Driver: cgroupfs Plugins: Volume: local Network: bridge null host Kernel Version: 4.4.9-moby Operating System: Alpine Linux v3.3 OSType: linux Architecture: x86_64 CPUs: 2 Total Memory: 3.858 GiB
13. • Uses the new HyperKit framework, which is in turn based on xHyve and FreeBSD's bHyve. • Sandbox friendly: processes largely run as non-root, with privileges of the local user. • Embeds Linux: includes an embedded lightweight Alpine Linux distribution optimised for fast boot and stateless operation for containers. • Drag 'n drop installation: Docker.app is self-contained, installs symlinks from app bundle into /usr/local, and autoupdates. Virtualisation
14. • Performance: The CPU performance of a Linux container is largely the same as when running the same compute on the Mac, since we use the hardware CPU virtualisation extensions. • Battery life: Some battery life hit due to running containers instead of MacOS X native processes, but not adverse for normal use. • Disk usage: The app manages disk usage via a qcow2 file in its data directory. This is a sparse file that is allocated on demand, up to a (current) maximum of 64GB of disk space. Can be excluded from Time Machine backups. Virtualisation
15. Networking Notworking
16. • Want to hide the gory details of virtualisation from the user. The Linux VM should be "invisible". • Not solving this leads to many user complaints: • VPN software and corporate installations do not like bridged virtual machines or custom routing.
 Result: container traffic cannot connect to Internet. • Services cannot be exposed on localhost or the external interface and are instead on the Linux VM IP address.
 Result: breaks common web oAuth workflows. Networking
17. • Challenge: Deal with custom VPN software on the host that makes it difficult to bridge. • Solution: VPNKit, efficiently reconstructs container traffic into separate TCP/IP flows and translates them into native OSX/Windows sockets. OSX Host Linux Host Container RUN <...> com.docker.hyperkit-net Reconstruct traffic TCP flows Translate to OSX socket calls Ethernet bridge DHCPv4 NTP Networking
18. • Challenge: Deal with custom VPN software on the host that makes it difficult to bridge. • Solution: VPNKit, efficiently reconstructs container traffic into separate TCP/IP flows and translates them into native OSX/Windows sockets. • Benefits: • All network traffic is generated from normal socket calls (e.g. gethostbyaddr) on the Mac, so interacts well with firewalls, VPNs, and any local security policies. Networking
19. OSX Host Linux Host Privileged Port Service Container EXPOSE Port Service VSock Binder RUN <...> VSock Listener Userland Proxy • Challenge: Services publishing ports should be exposed on localhost without needing VM info. • Solution: VPNKit forwards container port requests to a OSX service which binds them natively on its external interface. Networking
20. • Challenge: Services publishing ports should be exposed on localhost without needing VM info. • Solution: VPNKit forwards container port requests to a OSX service which binds them natively on its external interface. • Benefits: • docker run -P on the Mac now works without requiring any knowledge of the VM innards. • External oAuth workflows operate with web apps. Networking
21. Filesystems
22. • Challenge: Share arbitrary OSX directory tree into Linux container without requiring extensive modification of either side. • Solution: Use a FUSE forwarding layer and translate Linux filesystem calls to OSX equivalents. OSX Host Linux Host Container VOLUME com.docker.osxfs Track extra metadata Translate to OSX filesystem calls FUSE Filesystem Sharing
23. • Challenge: Need filesystem activation so events on the Mac wake up container servers and vice-versa. • Solution: osxfs uses FSEvents API and injects inotify activation events into container. OSX Host Linux Host Container VOLUME com.docker.osxfs FSEvents watches open files Events from Linux causes OSX apps to wake up FUSE Filesystem Sharing
24. •New osxfs engine that bind mounts OSX filesystem trees into Docker containers. •Daemon that listens bidirectionally on shared volumes and translates between OSX and Linux. Includes notifications, via FSEvents on Mac and inotify on Linux. •Runs as user and so cannot access system files on OSX host. Planning to further restrict host access in future. •Mount points for /Users, /Volumes, /private and /tmp from the Mac exist. •All requesting processes are treated as owners and group members on all bind mounted resources. User/group changes are persisted but not discriminated on. Filesystem Sharing
25. $ docker run resin/armv7hf-debian uname -a Linux 7ed2fca7a3f0 4.1.12 #1 SMP Tue Jan 12 10:51:00 UTC 2016 armv7l GNU/Linux $ docker run justincormack/ppc64le-debian uname -a Linux edd13885f316 4.1.12 #1 SMP Tue Jan 12 10:51:00 UTC 2016 ppc64le GNU/Linux Multi-CPU architectures
26. Questions? Sign up at beta.docker.com Twitter: @avsm https://github.com/docker/hyperkit https://github.com/docker/vpnkit https://github.com/docker/datakit
27. Cambridge hackathons coming up: MirageOS in mid-July for 2 days OCaml Compiler Hacking in August Contact Gemma Gordon <gg417@cl.cam.ac.uk> Beginners welcome!