HANet: a framework toward ultimately reliable network services

High availability is becoming an essential part of network services because even a little downtime may lead to a great loss of money. According to previous research, network failure is one of the major causes of system unavailability. In this paper, we propose a framework called HANet for building highly available network services. The main goal of HANet is to allow a server to continue providing services when all its network interfaces to the outside world (i.e., public interfaces) have failed. This is achieved by two techniques. First, a network interface can be backed up not only by other public network interfaces, but also by other interserver I/O communication interfaces (i.e., private interfaces) such as Ethernet, USB, RS232, etc. Therefore, IP packets can still be transmitted and received via these I/O links, even when all of the public network interfaces have failed. Second, HANet allows a server to take over the packet transmission job of another network-failed server. The benefit of HANet is that a network-failed server will not lose any requests which are being processed. And, it is efficient since no synchronization overhead or replaying process is required. Moreover, it is totally transparent to server applications and clients. To demonstrate the feasibility of HANet, we implemented it in the Linux kernel. According to the performance results, using a private Fast Ethernet interface for data communication leads to only 1% overhead in user-perceived latency when the public Fast Ethernet interface of the server has failed. This indicates that HANet is efficient, and hence is feasible for commercial network services. 2004 Elsevier Inc. All rights reserved.