Workgroup and Multi-site clusters in Windows Server 2016 

In Windows Server 2012 R2 and previous versions, a cluster could only be created between member nodes joined to the same domain. Windows Server 2016 breaks down these barriers and introduces the ability to create a Failover Cluster without Active Directory dependencies. Failover Clusters can now therefore be created in the following configurations:

• Single-domain Clusters: Clusters with all nodes joined to the same domain

• Multi-domain Clusters: Clusters with nodes which are members of different domains

• Workgroup Clusters: Clusters with nodes which are member servers / workgroup (not domain joined)

情報源: Workgroup and Multi-site clusters in Windows Server 2016 – Clustering and High-Availability – Site Home – MSDN Blogs

Windows Server 2016 TP3よりMuti Domain, Workgroup環境でのFailover Cluster機能が追加されるようです。ただし、DNSは必要ですし、参加するサーバーは共通のDNSサフィックスを持っている必要があります。

今までのシングルドメインでのフェイルオーバークラスタについてはそのままです。

上リンク先を見る限りあれって言うぐらいあっけない感じで設定されるようです。