1. A computer-implemented method for operating virtual resources, comprising: under control of one or more computer systems configured with executable instructions, providing virtual resources provisioned to use physical hardware resources of a virtual resource provider; providing a plurality of control planes within the virtual resource provider that perform management of at least some of the virtual resources, each of the default control planes including one or more of a plurality of default control plane modules to perform various management functionalities; establishing a custom virtual control plane that replaces one of the default control planes and that performs management of two or more of the virtual resources within the virtual resource provider, the custom virtual control plane being customizable through a control plane provisioning interface for selection of which control plane modules are associated with the custom virtual control plane, so that a user selects which of the control plane modules of the one of the default control planes are replaced with user selected custom control plane modules of the custom virtual control plane that performs management functionalities of the two or more virtual resources; receiving data from sensors coupled to the control plane modules of the custom virtual control plane and receiving data from sensors coupled to at least one of the plurality of default control plane modules; responsive to data received from the sensors, receiving at least a first resource configuration request from the custom virtual control plane and at least a second resource configuration request from the at least one of the plurality of default control planes, the first and second resource configuration requests specifying competing configurations for a capacity of a virtual resource, which is one of the physical hardware resources of the virtual resource provider, and which is shared by a control plane module of the custom virtual control plane and the at least one of the plurality of default control plane modules; mediating the first and second resource configuration requests so as to maintain the resource within its capacity, wherein mediating further includes modifying a resource allocation of the virtual resource to facilitate sharing between the control module of the custom virtual control plane and the at least one of the plurality of default control plane modules.