Project: LinuxKit (Provisioning / Automation & Configuration)
File: platform-hyperkit.md

We recommend using LinuxKit in conjunction with . For the time being it's best to be on the latest edge release. `linuxkit run` uses and and the edge release ships with updated versions of both. Alternatively, you can install HyperKit and VPNKit standalone and use it without Docker for Mac. The HyperKit backend currently supports booting: `kernel+initrd` output from `linuxkit build`. `kernel+squashfs` output from `linuxkit build`. EFI ISOs using the EFI firmware. You need to select the boot method manually using the command line options. The default is `kernel+initrd`. `kernel+squashfs` can be selected using `-squashfs` and to boot a ISO with EFI you have to specify `--iso --uefi`. The `kernel+initrd` uses a RAM disk for the root filesystem. If you have RAM constraints or large images we recommend using either the `kernel+squashfs` or the EFI ISO boot. With `linuxkit run` on HyperKit the serial console is redirected to stdio, providing interactive access to the VM. The output of the VM can be re-directed to a file or pipe, but then stdin is not available. HyperKit does not provide a console device. The HyperKit backend support configuring a persistent disk using the standard `linuxkit` `-disk` syntax. Multiple disks are supported and the disks are in raw format. HyperKit sends an ACPI power event when it receives SIGTERM to allow the VM to shut down properly. The VM has to be able to receive ACPI events to initiate the shutdown. This is provided by the . An example is available in the . By default, `linuxkit run` creates a VM with a single network interface which, logically, is attached to a L2 bridge. The bridge also has the VM used by Docker for Mac attached to it. This means that the LinuxKit VMs, created with `linuxkit run`, can be accessed from containers running on Docker for Mac. The LinuxKit VMs have IP addresses on the `192.168.65.0/24` subnet assigned by a DHCP server part of VPNKit. `192.168.65.1` is reserved for VPNKit as the default gateway and `192.168.65.2` is used by the Docker for Mac VM. By default, LinuxKit VMs get incrementally increasing IP addresses, but you can assign a fixed IP address with `linuxkit run -ip`. It's best to choose an IP address from the DHCP address range above, but care must be taken to avoid clashes of IP address. NOTE: The LinuxKit VMs can not be directly accessed by IP address from the host. Enabling this would require use of the macOS `vmnet` framework, which requires the VMs to run as `root`. We don't consider this option palatable, and provide alternative options to access the VMs over the network below. `hyperkit` offers a number of ways for accessing network services running inside the LinuxKit VM from the host. These depend on the networking mode selected via `-networking`. The default mode is `docker-for-mac` where the same VPNkit instance is shared between LinuxKit VMs and the VM running as part of Docker for Mac. The simplest way to access networking services exposed by a LinuxKit VM is to use a Docker for Mac

For example, to access an ssh server in a LinuxKit VM, create a ssh client container from: ``` FROM alpine:edge RUN apk add --no-cache openssh-client ``` and then run ``` docker build -t ssh . docker run --rm -ti -v ~/.ssh:/root/.ssh ssh ssh <IP address of VM> ``` A `socat` container on Docker for Mac can be used to proxy between the LinuxKit VM's ports and localhost. For example, to expose the redis port from the , use this Dockerfile: ``` FROM alpine:edge RUN apk add --no-cache socat ENTRYPOINT [ "/usr/bin/socat" ] ``` and then: ``` docker build -t socat . docker run --rm -t -d -p 6379:6379 socat tcp-listen:6379,reuseaddr,fork tcp:<IP address of VM>:6379 ``` There is experimental support for exposing selected ports of the guest on `localhost` using the `-publish` command line option. For example, using `-publish 2222:22/tcp` exposes the guest TCP port 22 on localhost on port 2222. Multiple `-publish` options can be specified. For example, the image build from the [`sshd example`](../examples/sshd.yml) can be started with: ``` linuxkit run -publish 2222:22/tcp sshd ``` and then you can log into the LinuxKit VM with `ssh -p 2222 root@localhost`. Note, this mode is experimental and may cause the VPNKit instance shared with Docker for Mac being confused about which ports are currently in use, in particular if the LinuxKit VM does not exit gracefully. This can typically be fixed by restarting Docker for Mac. An alternative to the previous method is to start your own copy of `vpnkit` (or connect to an already running instance). This can be done using the `-networking vpnkit` command line option. VPNKit uses a 9P mount in `/port` for coordination between components. The first VM on a VPNKit instance currently needs mount the 9P filesystem and also needs to run the `vpnkit-forwarder` service to enable port forwarding to localhost. A full example with `vpnkit` forwarding of `sshd` is available in . To run this example with its own instance of VPNKit, use: ``` linuxkit run -networking vpnkit -publish 2222:22/tcp vpnkit-forwarder ``` You can then access it via: ``` ssh -p 2222 root@localhost ``` More details about the VPNKit forwarding mechanism is available in the [VPNKit documentation](https://github.com/moby/vpnkit/blob/master/docs/ports.md#signalling-from-the-vm-to-the-host). There are no special integration services available for HyperKit, but there are a number of packages, such as `vsudd`, which enable tighter integration of the VM with the host (see below). The HyperKit backend also allows passing custom userdata into the using either the `-data` or `-data-file` command-line option. This attaches a CD device with the data on. The provides a daemon that exposes unix domain socket inside the VM to the host via virtio or Hyper-V sockets. With HyperKit, the virtio sockets can be exposed as unix domain sockets on the host, enabling access to other daemons, like `containerd` and `dockerd`, from the host. An example configuration file is available in . After building the example, run it with `linuxkit run hyperkit -vsock-ports 2374 vsudd`. This will create a unix domain socket in the state directory that maps to the `containerd` control socket. The socket is called `guest.00000946`. If you install the `ctr` tool on the host you should be able to access the `containerd` running in the VM: ``` $ go get -u -ldflags -s github.com/containerd/containerd/cmd/ctr ... $ ctr -a vsudd-state/guest.00000946 list ID IMAGE PID STATUS vsudd 466 RUNNING ```