市场上的Hypervisor很多，有最流行的VMWare，有比较小众讲究可靠性的Stratus EverRun. 现在的服务器硬件非常便宜，跟VMWare提供差不多功能的Hyper V是Windows免费提供的一项功能。Windows不仅可以只是当作个人电脑处理文档和上网，更可以作为企业级服务器用作虚拟机器(Virtual Machine)的主机(Hypervisor)，并可以组成failover cluster提高可靠性(High Availability)。

Here we explain how Windows Hyper-V and Windows Failover Cluster work.

1. You can download the latest Windows 2022 server from Microsoft. It's free Evaluation version for 180 days

2. Hyper-V and failover cluster are free build in features from Windows server. After the installation, we can create Virtual Machine using Hyper-V. The OS of VM can be Linux or Windows. You can download free Linux OS from Oracle, or Ubuntu or any other OS, and install the OS on VM.

3. To create a failover cluster, we need to do the below.

   a) Install the same Windows server on two physical servers. There are inter-connections between the two servers for heartbeat.

   b) There must be some shared storage between the two servers. We can use starwind to implement this shared storage. Starwind has free version, pls refer to their website.

   c) Create one or two VM using Hyper-V on one or two physical server under local storage, enable Active Directory and DNS service. Make one VM as Primary AD server, and another server as secondary AD server.

      > Set-DnsClientServerAddress -InterfaceIndex 4 -ServerAddresses ("192.168.2.204","8.8.8.8")

      > Install-WindowsFeature -name AD-Domain-Services -IncludeManagementTools

      > Install-ADDSForest -DomainName "Your Domain Name"

      > Add-DnsServerPrimaryZone -NetworkID "192.168.2.0/24" -ReplicationScope "Server Domain Name"

   d) All the servers and VMs shall join the AD and register Domain name

   e) Create VM under Starwind shared storage

   f) Install Linux or Windows on the failover VM

4. When the active physical server is down, the VM will be failed over to the secondary physical server. For planned activity, you can use Live migration to failover a VM without any downtime.