docs: hyper-v: add documentation

* added basic installation requirements
* added powershell script to create a Gen 1 and Gen 2 VM
* added powershell script to create and use a configdrive
* added a butane config with advanced features like auto-login, password set and TPM cryptenroll

Signed-off-by: Adrian Vladu <avladu@cloudbasesolutions.com>

content/docs/latest/_index.md

@@ -39,6 +39,7 @@ purposes. You can use any of the following options.
  * [libVirt][libvirt]
  * [VirtualBox][virtualbox] (not officially supported)
  * [Vagrant][vagrant] (not officially supported)
+ * [Hyper-V][hyper-v] (not officially supported)
 
 #### Bare Metal
 You can install Flatcar on bare metal machines in different ways: using ISO
@@ -191,6 +192,7 @@ Flatcar tutorial to deep dive into some Flatcar fundamental concepts.
 [libvirt]: installing/vms/libvirt
 [virtualbox]: installing/vms/virtualbox
 [vagrant]: installing/vms/vagrant
+[hyper-v]: installing/vms/hyper-v
 [vmware]: installing/cloud/vmware
 [cluster-architectures]: setup/clusters/architectures
 [update-strategies]: setup/releases/update-strategies

content/docs/latest/installing/vms/hyper-v.md

@@ -0,0 +1,156 @@
+---
+title: Running Flatcar Container Linux on Hyper-V
+linktitle: Running on Hyper-V
+weight: 30
+---
+
+_While we always welcome community contributions and fixes, please note that Hyper-V is not an officially supported platform at this time because the release tests don't run for it. (See the [platform overview](/#installing-flatcar).)_
+
+These instructions will walk you through running Flatcar Container Linux on Hyper-V.
+
+## Choose a channel
+
+Flatcar Container Linux is designed to be updated automatically with different schedules per channel. You can [disable this feature][update-strategies], although we don't recommend it. Read the [release notes][release-notes] for specific features and bug fixes.
+
+Hyper-V images are created only for AMD64 and come in two disk formats, VHD for Hyper-V VM Generation 1 and VHDX for both Hyper-V Generation 1 and 2 VMs.
+
+Note: Hyper-V Generation 2 virtual machines need to have secure boot disabled, as the VHDX images are not signed.
+
+How to download a VHDX image file:
+
+```powershell
+# VHDX image is available for download from the current Alpha onwards
+curl.exe --progress-bar -LO "https://bincache.flatcar-linux.net/images/amd64/3937.0.0+nightly-20240411-2100/flatcar_production_hyperv_vhdx_image.vhdx.zip"
+Expand-Archive flatcar_production_hyperv_vhdx_image.vhdx.zip .
+```
+## Creating a config-drive
+
+While Ignition is not supported on a config-drive, you can provide a Cloud-config following the coreos-cloudinit subset.
+
+The cloud-config can be specified by attaching a [config-drive](https://github.com/flatcar/coreos-cloudinit/blob/master/Documentation/config-drive.md) with the label `config-2`. This is commonly done through whatever interface allows for attaching CD-ROMs or new drives.
+
+Note that the config-drive standard was originally an OpenStack feature, which is why you'll see strings containing `openstack`. This filepath needs to be retained, although Flatcar Container Linux supports config-drive on all platforms.
+
+For more information on customization that can be done with cloud-config, head on over to the [cloud-config guide](https://github.com/flatcar/coreos-cloudinit/blob/master/Documentation/cloud-config.md).
+
+You need a config-drive to configure at least one SSH key to access the virtual machine. If you are in hurry, you can create a basic config-drive on Windows with following steps:
+
+```powershell
+#ps1
+# mkisofs can be downloaded from https://github.com/cloudbase/cloudbase-init-test-resources/tree/master/bin
+# create an Openstack config drive folder structure
+mkdir config-drive-metadata/openstack/latest
+echo '{"hostname": "my_flatcar_01.local", "name": "my_flatcar_01", "public_keys": {"userkey": "INSERT_HERE_PUBLIC_SSH_KEY"}' > config-drive-metadata/openstack/latest/meta_data.json
+# create the config drive
+& "mkisofs.exe" -o "config-drive.iso" -ignore-error -ldots -allow-lowercase -allow-multidot -l -publisher "cbsl" -quiet -J -r -V "config-2" "config-drive-metadata"
+```
+
+An ISO file named `config-drive.iso` will be created that will configure a virtual machine to accept your SSH key and set its name to my_flatcar_01.
+
+## Deploying a new virtual machine on Hyper-V using config drive
+
+```powershell
+$vmName = "my_flatcar_01"
+$vmDisk = "flatcar_production_hyperv_vhdx_image.vhdx"
+
+# For Generation 1 VM
+New-VM -Name $vmName -MemoryStartupBytes 2GB `
+    -BootDevice VHD -SwitchName "Default Switch" -VHDPath $vmDisk -Generation 1
+
+# For Generation 2 VM
+New-VM -Name $vmName -MemoryStartupBytes 2GB `
+    -BootDevice VHD -SwitchName "Default Switch" -VHDPath $vmDisk -Generation 2
+# Generation 2 VM needs to have secure boot disabled, as the images are not signed
+Set-VMFirmware -EnableSecureBoot "Off" -VMName $vmName
+
+# Now, add the config-drive file as DvdDrive
+Add-VMDvdDrive -VMName $vmName -Path "config-drive.iso"
+
+Start-VM -Name $vmName
+```
+
+## Advanced example: deploying a new virtual machine on Hyper-V using Ignition with autologin and TPM LUKS2 root partition encryption
+
+```powershell
+$vmName = "my_flatcar_01"
+$vmDisk = "flatcar_production_hyperv_vhdx_image.vhdx"
+
+New-VM -Name $vmName -MemoryStartupBytes 2GB `
+    -BootDevice VHD -SwitchName "Default Switch" -VHDPath $vmDisk -Generation 2
+Set-VMFirmware -EnableSecureBoot "Off" -VMName $vmName
+
+# The core user password is set to foo
+
+$ignitionMetadata = @'
+variant: flatcar
+version: 1.0.0
+kernel_arguments:
+  should_exist:
+    - flatcar.autologin
+passwd:
+  users:
+    - name: core
+      password_hash: $6$sn3ZSJJJln5JkAZb$VDTKzLpCyjlEe7Kh0DKjOnEawkkOoi0tOKVbcCv0FIWSf3u9Y1p1I5YdJJ5L8uDmmMvO2CBlmJZNdxFuekjjE1
+storage:
+  luks:
+  - name: rootencrypted
+    wipe_volume: true
+    device: "/dev/disk/by-partlabel/ROOT"
+  filesystems:
+    - device: /dev/mapper/rootencrypted
+      format: ext4
+      label: ROOT
+systemd:
+  units:
+    - name: cryptenroll-helper.service
+      enabled: true
+      contents: |
+        [Unit]
+        ConditionFirstBoot=true
+        OnFailure=emergency.target
+        OnFailureJobMode=isolate
+        [Service]
+        Type=oneshot
+        RemainAfterExit=yes
+        ExecStart=systemd-cryptenroll --tpm2-device=auto --unlock-key-file=/etc/luks/rootencrypted --wipe-slot=0 --tpm2-pcrs= /dev/disk/by-partlabel/ROOT
+        ExecStart=rm /etc/luks/rootencrypted
+        [Install]
+        WantedBy=multi-user.target
+'@
+echo $ignitionMetadata > ignition.yaml
+
+# download the butane binary to create the raw ignition metadata
+# https://github.com/coreos/butane/releases
+curl.exe -sLO "https://github.com/coreos/butane/releases/download/v0.20.0/butane-x86_64-pc-windows-gnu.exe"
+
+# transform the Ignition metadata from Butane format to Ignition raw
+.\butane-x86_64-pc-windows-gnu.exe ".\ignition.yaml" -o ".\ignition.json"
+
+# download the tool kvpctl to set the Ignition metadata from
+# https://github.com/containers/libhvee/releases
+# See: https://docs.fedoraproject.org/en-US/fedora-coreos/provisioning-hyperv/
+curl.exe -sLO "https://github.com/containers/libhvee/releases/download/v0.7.1/kvpctl-amd64.exe.zip"
+Expand-Archive kvpctl-amd64.exe.zip .
+.\kvpctl-amd64.exe "$vmName" add-ign ignition.json
+
+Set-VMKeyProtector -VMName $vmName -NewLocalKeyProtector
+Enable-VMTPM -VMName $vmName
+
+Start-VM -Name $vmName
+```
+
+A more complete TPM2 example can be found at [security-luks][security-luks].
+
+At boot time, the Flatcar Container Linux will detect that the volume size has changed and will resize the filesystem accordingly.
+
+Currently, there is no support for the Hyper-V guest to hypervisor communication, useful for virtual machine IP retrieval.
+
+## Using Flatcar Container Linux
+
+Now that you have a machine booted it is time to play around. Check out the [Flatcar Container Linux Quickstart][quickstart] guide or dig into [more specific topics][doc-index].
+
+[update-strategies]: ../../setup/releases/update-strategies
+[security-luks]: ../../setup/security/luks
+[release-notes]: https://flatcar-linux.org/releases
+[quickstart]: ../
+[doc-index]: ../../