Virtualization by itself, however, is not a complete utility computing solution. While virtualization systems deal exceptionally well with partitioning CPU and memory within a server, they lack abstractions for network and storage interactions, image management, life-cycle control and other services critical to utility computing. However, there are two commercial utility computing solutions based on virtualization that are more than a year old now, Amazon’s EC2 and 3tera’s AppLogic.and here on Network dilemma :
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When installing software on a physical server or virtual machine it’s normal practice for each system to be configured with the name or IP addresses of numerous other resources within the data center. For instance, a web server may have the name of a database or NAS. In a utility system, however, configuration isn’t quite so simple.
Xen’s network configuration provides two mechanisms: (1) flat L2 network, in which domain 0 acts also as a network switch, forwarding packets between the physical network and the VMs; and (2) routed solution, in which domain 0 acts as an IP router, creating a subnet for all VMs on the same server. Both approaches create their own set of problems when used in utility computing systems — from exceeding the MAC address limits on L2 switches to complicating the IP address space and preventing live migration of VMs.
Most existing utility systems implement either point-to-point connection virtualization or security groups similar to VLANs. As with storage, some form of quota or throttling of network I/O is needed so that one VM cannot monopolize the network interface and starve other VMs. In addition, network virtualization services like better VLAN systems, DHCP and DNS variants that take VM and utility needs into account are needed.