“Insufficient resources to satisfy configured failover level for vSphere HA”

Not a message you wanted to see in your environment, especially a heavily virtualized one.  Nor is it particularly clear*.  There was a lack of resources, but where?  What type? CPU? RAM? VCenter knew but wasn’t sharing.
An entry in the VMWare forums pointed me to the page to looking in VCenter.  Of particular use was the reply by jjkrueger.
In short,

  1. Go to the Home->Inventory->Hosts and Clusters page
  2. Click on the Cluster you want to inspect
  3. Select the Resource Allocation Tab
  4. Select a View (cpu/memory/storage)

In this case, it was memory.  Almost all the virtual machines had the “Reserve all guest memory” option enabled.
Original forum post: http://communities.vmware.com/message/2019314
*  Unless you already know what it means.