These alternative configurations may be appropriate in limited cases, such as a test cluster, but are not the best method in most situations. They are presented here for completeness and as an example of Pacemaker’s flexibility to suit your needs.
6.1. Virtual Machines as Cluster Nodes
The preferred use of virtual machines in a Pacemaker cluster is as a cluster resource, whether opaque or as a guest node. However, it is possible to run the full cluster stack on a virtual node instead.
This is commonly used to set up test environments; a single physical host (that does not participate in the cluster) runs two or more virtual machines, all running the full cluster stack. This can be used to simulate a larger cluster for testing purposes.
In a production environment, fencing becomes more complicated, especially if the underlying hosts run any services besides the clustered VMs. If the VMs are not guaranteed a minimum amount of host resources, CPU and I/O contention can cause timing issues for cluster components.
Another situation where this approach is sometimes used is when the cluster owner leases the VMs from a provider and does not have direct access to the underlying host. The main concerns in this case are proper fencing (usually via a custom resource agent that communicates with the provider’s APIs) and maintaining a static IP address between reboots, as well as resource contention issues.
