In a heterogeneous environment of virtual machines, an agent can migrate between virtual machines of different types. During migration, classes of the mobile agent may need to be instantiated on the new virtual machine. To support classes across all virtual machine types, a resource server is provided that can provide virtual machine type specific instances of the classfile. The resource server receives a resource request from a resource loader of a virtual machine. The resource request specifies the resource and the virtual machine type, thereby enabling the resource server to retrieve the correct instance of the classfile to return to the resource loader.