1 Migratory TCP: Connection Migration for Service Continuity in the Internet* Florin Sultan, Kiran Srinivasan, Deepa Iyer, Liviu Iftode Department of Computer Science Rutgers University *Work supported in part by the NSF under grant CCR

2 Today: TCP-based Internet Services TCP : reliable byte-stream Client Server

3 The Problem with TCP Adverse conditions internetwork congestion or failure server overloaded, failed or under DoS attack TCP response network delays => packet loss => retransmission TCP limitations addressing: implicitly binds the service to a server error recovery: limited to one server

4 Highly Available Server? Not Enough! To a TCP client: connect() will succeed most of the time To an end-user: may not help beyond connect() connectivity failures, server overload, etc. Service continuity = uninterrupted end-to-end delivery of a service as important to end-user as the high availability of the server!

5 Our Solution: Cooperative Service Model Client Server 1 Server 2 congestion Logically equivalent servers cooperate in sustaining the service by migration of live connections

6 Migratory TCP (M-TCP) A client connection transparently migrates to different servers during its lifetime server applications cooperate to support the handoff client application does not change servers can be geographically distributed Designed and implemented as a TCP extension Mechanism decoupled from migration policy policies are not the focus of this talk

7 Per-connection State Server 1Server 2 Application M-TCP Application M-TCP Application state Protocol state

8 Application - M-TCP Service Contract Application Define fine-grained per-connection application state Export a per-connection application state snapshot to the protocol Import per-connection state after migration and resume service M-TCP Transfer per-connection state Synchronize application state with protocol state

9 Server Migration API export_state(conn, state_buff) origin server, periodically during service on connection import_state(conn, state_buff) destination server, after accepting connection origin destination Application export() import() M-TCP

10 Connection Migration Mechanism C C’C’ (2) (3) Client Server 1 Server 2 (1) (4)

11 Prototype Implementation Modified TCP/IP stack in the FreeBSD kernel Real applications Icecast audio streaming server migrate audio stream PostgreSQL transactional DB server front-end migrate sequence of transactions with ACID semantics Apache web server migrate transfer of static files, dynamic content

12 Experimental Setup S1 S2 C Hub Control interface Service interface

13 Streaming Server Experiment Effective throughput close to average rate seen before server performance degrades

14 Related Work HTTP server fail-over by connection migration [Snoeren ‘00] soft TCP and HTTP state maintained at back-up servers application-specific: relies on HTTP features Fault-tolerant TCP [Alvisi ‘00] persistent connections across server crashes failures masked using TCP wrappers Stream Control Transmission Protocol [RFC 2960] multi-homing preserves connectivity if network fails

15 Conclusions Transport layer protocol that supports service continuity dynamic, light-weight, transparent connection migration Migration API for server applications Working prototype for FreeBSD & real applications

16 Future Work Multi-process state migration application state spans multiple processes that communicate via IPC channels Non-intrusive state transfer by remote memory access (VIA, InfiniBand) A distribution of the M-TCP software for FreeBSD will be available this fall

17 Google: Migratory TCP or M-TCP Thank you!