Toward Fault-Tolerant P2P Systems: Constructing a Stable Virtual Peer from Multiple Unstable Peers

P2P systems must handle unexpected peer failure and leaving, and thus it is more difficult to implement than server-client systems. In this paper, we propose a novel approach to implement P2P systems by using virtual peers. A virtual peer consists of multiple unstable peers. A virtual peer is a stable entity; application programs run on a virtual peer are not compromised unless a majority of the peers fail within a short time duration. If a peer in a virtual peer fails, the failed peer is replaced by another (non-failed) one to restore the number of working peers. The primary contribution of this paper is to propose a method to form a stable virtual peer over multiple unstable peers. The major challenges are to maintain consistency between multiple peers and to replace a failed peer with another one. For the first issue, the Paxos consensus algorithm is used. For the second issue, the process migration technique is used to replicate and transfer a running process to a remote peer. Furthermore, the relation between the reliability of a virtual peer and the number of peers assigned to a virtual peer is evaluated. The proposed method is implemented in our musasabi P2P platform. An overview of musasabi and its implementation is also given.