Identify the missing word(s) in the following sentence within the context of Microsoft Azure. For all availability configurations of availability groups (AGs), an underlying cluster is required. There are many aspects of setting up a cluster that you need to be aware of. Deploying a Windows Server Failover Cluster (WSFC) in Azure is similar to configuring one on premises. One of the most important aspects is deciding what to use for a witness resource. Witness is a core component of the [?] mechanism. This is what helps ensure that everything in the WSFC stays up and running. If you lose [?], the WSFC will go down taking an AG or FCI with it.