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Introduction to Content-aware Switch

Introduction to Content-aware Switch. Presented by Li Zhao. Content-aware Switch (CS). www.yahoo.com. Internet. Image Server. IP. TCP. APP. DATA. Application Server. Switch. GET /cgi-bin/form HTTP/1.1 Host: www.yahoo.com…. HTML Server. Front-end of a web cluster

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Introduction to Content-aware Switch

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  1. Introduction to Content-aware Switch Presented by Li Zhao

  2. Content-aware Switch (CS) www.yahoo.com Internet Image Server IP TCP APP. DATA Application Server Switch GET /cgi-bin/form HTTP/1.1 Host: www.yahoo.com… HTML Server • Front-end of a web cluster • Route packets based on layer 5/7 (content) information

  3. Why use CS • Servers can be specialized for certain types of request • Content segregation • Exploit locality • Affinity-based routing • Increase the performance because of the improved hit rate • Partial replication of server file set • Partition the server’s file set over different nodes

  4. Content-aware Switch Architecture • Two way architecture • Server returns the • response to the switch • One way architecture • Server returns the • response to the client client switch server [Valeria01]

  5. Layer 7 Two-way Architecture

  6. Layer-7 Two-way Mechanisms • TCP gateway An application level proxy running on the web switch mediates the communication between the client and the server • TCP splicing reduce the overhead in TCP gateway. Packet forwarding occurs at network level between the network interface driver and the TCP/IP stack, is carried out directly by OS user kernel user kernel

  7. SYN(CSEQ) step4 SYN(SSEQ) step5 ACK(CSEQ+1) step6 DATA(CSEQ+1) ACK(SSEQ+1) TCP Splicing client server content switch SYN(CSEQ) step1 SYN(DSEQ) step2 ACK(CSEQ+1) DATA(CSEQ+1) step3 ACK(DSEQ+1) step7 DATA(DSEQ+1) DATA(SSEQ+1) ACK(CSEQ+LenR+1) ACK(CSEQ+lenR+1) step8 ACK(DSEQ+ lenD+1) ACK(SSEQ+lenD+1) lenR: size of http request. . lenD: size of return document

  8. TCP Splicing w/ Pre-forked Connections switch client server SYN(PSEQ) step1 SYN(SSEQ) step2 ACK(PSEQ+1) ACK(SSEQ+1) step3 SYN(CSEQ) step4 SYN(DSEQ) step5 ACK(CSEQ+1) DATA(CSEQ+1) step6 ACK(DSEQ+1) DATA(PSEQ+1) step7 ACK(SSEQ+1) DATA(DSEQ+1) DATA(SSEQ+1) step8 ACK(CSEQ+LenR+1) ACK(PSEQ+lenR+1) ACK(DSEQ+ lenD+1) ACK(SSEQ+lenD+1) step9 lenR: size of http request. Ref [Yang99] . lenD: size of return document

  9. SYN(CSEQ) SYN(CSEQ) step1 SYN(SSEQ) SYN(SSEQ) step2 ACK(CSEQ+1) ACK(CSEQ+1) step3 DATA(CSEQ+1) DATA(CSEQ+1) ACK(SSEQ+1) ACK(SSEQ+1) step4 DATA(SSEQ+1) DATA(SSEQ+1) ACK(CSEQ+LenR+1) ACK(CSEQ+lenR+1) step5 lenD+1) ACK(SSEQ+ ACK(SSEQ+lenD+1) Pre-Allocate Server Scheme Pre-allocated server client content switch • Use a guess routing decision based on IP/Port#/History • Advantage: • Faster than TCP splicing. • Reduce session processing overhead no need to convert server sequence # Ref [Edward]

  10. SYN(CSEQ) step4 SYN(RSEQ) step5 ACK(CSEQ+1) step6 DATA(CSEQ+1) ACK(SSEQ+1) Degenerated to TCP Splicing If Guess Wrong Pre-allocated server client content switch SYN(CSEQ) SYN(CSEQ) step1 SYN(SSEQ) SYN(SSEQ) step2 ACK(CSEQ+1) ACK(CSEQ+1) step3 DATA(CSEQ+1) FIN(CSEQ+1) ACK(SSEQ+1) Right server step4 DATA(SSEQ+1) DATA(RSEQ+1) ACK(CSEQ+LenR+1) ACK(CSEQ+lenR+1) step5 lenD+1) ACK(DSEQ+ ACK(SSEQ+lenD+1) Sequence # conversion needed

  11. Case Study • Linux-based content aware switch [Yang99] • IBM Layer 5 [Pradhan00]

  12. Functional Overview of Content-aware Distributor Ref [Yang99]

  13. Results • Overhead of the switch • 89usec reduced  pre-forked connections • CS vs. Layer 4 switch • Affinity-based routing vs. WRR • Content-segregation vs. WRR • CGI: 27% • Static: 36%

  14. IBM Switch Architecture • Switch core • Port controller: • Identify packets (layer 5) and send them to CPU • Processing all other packets • CPU: PowerPC 603e • Parse http request • URL based routing Ref [Pradhan99]

  15. Flow Diagram on Layer 5 System • Client ports vs. server ports • Classifier: Identify packets

  16. Results • CS vs. Layer 4 switch • Entire set of files are replicated • Some servers share files by NFS • Partitioned file set

  17. Layer-7 one-way architecture

  18. Layer-7 one-way mechanisms • TCP handoff The switch hands off the TCP connection endpoint to the server • TCP connection hop • Software-based proprietary solution • encapsulating the IP packet in an RPX packet and sending it to the server.

  19. TCP Handoff client content switch server SYN(CSEQ) step1 SYN(DSEQ) step2 ACK(CSEQ+1) DATA(CSEQ+1) step3 ACK(DSEQ+1) Migrate(Data, CSEQ, DSEQ) step4 DATA(DSEQ+1) step5 ACK(CSEQ+lenR+1) step6 ACK(DSEQ+ lenD+1) ACK(DSEQ+lenD+1) • Migrate the created TCP connection from the switch to the back-end sever • Create a TCP connection at the back-end without going through the TCP three-way handshake • Retrieve the state of an established connection and destroy the connection without going through the normal message handshake required to close a TCP connection • Once the connection is handed off to the back-end server, the switch must forward packets from the client to the appropriate back-end server [Pai98]

  20. Case Study • Scalable content-aware request distribution in cluster-based network servers [Aron00]

  21. TCP Handoff (1) a client connects to the front-end (2) the dispatcher at the front-end accepts the connection and hands it off to a back-end server using the handoff protocol (3) the back-end takes over the established connection received by the handoff protocol (4) the server at the back-end accepts the created connection (5) the server at the back-end sends replies directly to the client

  22. Scalability of a single Front-end

  23. Scalable Cluster Design • Switch • Dispatcher component • Implement the request distribution: decide which server should handle request • 0.8usec • Distributor component • Distribute the client requests to the server (handoff or splicing) • 300usec for handoff, >750usec for splicing

  24. Cluster Operation (1) The layer 4 switch receives a SYN packet, choose the least loaded distributor (2) the distributor accepts the TCP connection and parses the client request (3) the distributor contacts the dispatcher for the assignment of the request to a server (4) the distributor hands off the connection using TCP handoff protocol to the server (5) the server takes over the connection using its handoff protocol (6) the server application at the server node accepts the connection (7) The server sends the response directly to the client (8) (not shown) the switch forward TCP acknowledgments to the corresponding server

  25. Results • The proposed cluster architecture scales far better than the one with a single front-end node.

  26. Host CPU PCI Bus StrongARM M E M E M E M E M E M E IX Bus MAC Our Current Research on CS • IXP 1200 • StrongARM @ 233MHz • Microengine(6) • IXP 2400 • Xscale @ 700MHz • Microengines(8)

  27. Our Design

  28. Using TCP Splicing

  29. Results

  30. References • [Pradhan00] G.Apostolopoulos, et. al, Design, Implementation and Performance of a Content-Based Switch, proceedings of IEEE INFOCOM-2000 • [Pai98] V.S. Pai, et. al, Locality-Aware Request Distribution in Cluster-based Network Servers. In Proceedings of the 8th Conference on Architectural Support for Programming Languages and Operating Systems, San Jose, CA, Oct.1998 • [Aron00] Mohit Aron et. al, Scalable Content-aware Request Distribution in Cluster-based Network Servers, Proc. of the 2000 Annual Usenix Technical Conference, June 2000 • [Edward] C. Edward Chow Chow, Introduction to content switch • [Valeria01] Valeria Cardellini, et. al, The state of the Art in Locally Distributed Web-server Systems, IBM research report • [Yang99] Chu-Sing Yang, et. Al, Efficient support for content-based rouging in web server clusters, Proc. Of USITS’ 99

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