Ensuring cloud computing performance on data communications networks, Part 2
The widely used Carrier Ethernet specifications from the Metro Ethernet Forum (MEF) solve these problems. The MEF model includes creation of an “Ethernet Virtual Connection” (EVC) between two User Network Interface (UNI) Ethernet ports that provide points of access for communication services. In a cloud access scenario, one UNI is at the customer site and another UNI is at the cloud service provider.The MEF is in the process of defining new specifications for providing convenient methods of provisioning or dynamically setting many EVCs from multiple locations to one location in a hub-and-spoke topology. Today the MEF defines encapsulation of EVC traffic across Carrier Ethernet networks using VLAN tags. According to 802.1ad, in the future there may be new encapsulations.MEF QoS specifications define traffic service-level agreements (SLAs) per EVC. SLAs include a traffic profile descriptor and traffic delivery guarantees that apply to the traffic within the profile. The traffic profile contains parameters like Committed Information Rate (CIR), Excess Information Rate (EIR), and Committed Burst Size. CIR, also sometimes called minimum or guaranteed rate, defines the average traffic rate that must be delivered across the network with performance guarantees. Committed Burst Size defines how bursty or uneven the instantaneous traffic rate may be so that it still can be considered within profile. EIR (also sometimes called maximum rate) defines an average traffic rate on top of the CIR that may be delivered by the network if the network is not congested.Server-to-server communication occurs among the application servers within the cloud. This communication happens in very specific and well-defined scenarios. The server-to-server RP is shown at Point 2 in the figure above.An example of server-to-server communication is when the application uses multiple geographically distributed machines to work together to accomplish certain intensive computing tasks. This is sometimes called clustered applications. Often these computers are collocated, and therefore the high bandwidth they require is relatively inexpensive to provision in a data center environment.Another example of server-to-server communication requirements is when a virtual machine with applications running on it is migrated from one physical box to another. This may be done for load-balancing, maintenance, or other operational reasons. This presents a different communications challenge for the cloud network.For a virtual machine to be moved smoothly and semi-transparently for the client, it is better to be moved with its IP address unchanged. This way the state of the TCP connection is preserved inside the networking stack and the communication may be resumed immediately after the virtual machine state image is transferred to another box. The fact that the IP address does not change means that servers must be connected at Layer 2, which fits well with the MEF Layer 2 communication model.Bandwidth-wise, migration of a virtual machine usually requires communication of gigabytes of traffic between machines. If it is to be done within a reasonable amount of time, up to 1-Gbps sustained-rate bandwidth should be provided. No encryption of traffic is required in this case since the information is not application-specific and is communicated in a controlled cloud environment, often within the same room, building, or campus.