Introduction to Content-aware Switch

Presented by

Li Zhao

Content-aware Switch (CS)

Switch

Image Server

Application Server

HTML Server

www.yahoo.comInternet

GET /cgi-bin/form HTTP/1.1 Host: www.yahoo.com…

APP. DATATCPIP

• Front-end of a web cluster• Route packets based on layer 5/7 (content)

information

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

Content-aware Switch Architecture

• Two way architectureServer returns theresponse to the switch

• One way architectureServer returns theresponse to the client

serverswitchclient

[Valeria01]

Layer 7 Two-way Architecture

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

kernel

user

kernel

user

TCP Splicingclient

content switch server

step1

step2

SYN(CSEQ)

SYN(DSEQ)

ACK(CSEQ+1)

DATA(CSEQ+1)

ACK(DSEQ+1)step3

step7

step8

step4

step5

step6

SYN(CSEQ)

SYN(SSEQ) ACK(CSEQ+1)

DATA(CSEQ+1) ACK(SSEQ+1)

DATA(SSEQ+1) ACK(CSEQ+lenR+1)

DATA(DSEQ+1) ACK(CSEQ+LenR+1)

ACK(DSEQ+lenD+1) ACK(SSEQ+lenD+1)

lenR: size of http request. lenD: size of return document

.

TCP Splicing w/ Pre-forked Connections

client

switch

server

step1

step2

SYN(CSEQ)

SYN(DSEQ)

ACK(CSEQ+1)

DATA(CSEQ+1)

ACK(DSEQ+1)

step3

step7

step8

step4

step5

step6

DATA(PSEQ+1)

ACK(SSEQ+1)

DATA(SSEQ+1)

ACK(PSEQ+lenR+1)

DATA(DSEQ+1) ACK(CSEQ+LenR+1)

ACK(DSEQ+lenD+1) ACK(SSEQ+lenD+1)

lenR: size of http request. lenD: size of return document

.

SYN(PSEQ)

SYN(SSEQ)ACK(PSEQ+1)

ACK(SSEQ+1)

step9

Ref [Yang99]

Pre-Allocate Server Schemeclient

content switch Pre-allocatedserver

step1

step2

SYN(CSEQ)

SYN(SSEQ)

ACK(CSEQ+1)

DATA(CSEQ+1)

ACK(SSEQ+1)step3

step4

step5

SYN(CSEQ)

SYN(SSEQ) ACK(CSEQ+1)

DATA(CSEQ+1) ACK(SSEQ+1)

DATA(SSEQ+1)ACK(CSEQ+lenR+1)

DATA(SSEQ+1)ACK(CSEQ+LenR+1)

ACK(SSEQ+lenD+1) ACK(SSEQ+lenD+1)

• 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]

Degenerated to TCP Splicing If Guess Wrong

client content switch

Pre-allocatedserver

step1

step2

SYN(CSEQ)

SYN(SSEQ)

ACK(CSEQ+1)

DATA(CSEQ+1)

ACK(SSEQ+1)step3

SYN(CSEQ)

SYN(SSEQ) ACK(CSEQ+1)

step4

step5

DATA(RSEQ+1)ACK(CSEQ+lenR+1)

DATA(SSEQ+1)ACK(CSEQ+LenR+1)

ACK(DSEQ+lenD+1) ACK(SSEQ+lenD+1)

FIN(CSEQ+1)

step4

step5

step6

SYN(CSEQ)

SYN(RSEQ) ACK(CSEQ+1)

DATA(CSEQ+1) ACK(SSEQ+1)

Right server

Sequence # conversion needed

Case Study

• Linux-based content aware switch [Yang99]

• IBM Layer 5 [Pradhan00]

Functional Overview of Content-aware Distributor

Ref [Yang99]

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%

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]

Flow Diagram on Layer 5 System

• Client ports vs. server ports• Classifier: Identify packets

Results

• CS vs. Layer 4 switch– Entire set of

files are replicated

– Some servers share files by NFS

– Partitioned file set

Layer-7 one-way architecture

Layer-7 one-way mechanisms

• TCP handoffThe 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.

TCP Handoffclient

content switch server

step1

step2

SYN(CSEQ)

SYN(DSEQ)

ACK(CSEQ+1)

DATA(CSEQ+1)

ACK(DSEQ+1)step3

step4

step5

step6

DATA(DSEQ+1)

ACK(CSEQ+lenR+1) ACK(DSEQ+lenD+1) ACK(DSEQ+lenD+1)

Migrate(Data, CSEQ, DSEQ)

• 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]

Case Study

• Scalable content-aware request distribution in cluster-based network servers [Aron00]

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

Scalability of a single Front-end

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

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

Results

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

Our Current Research on CS

Host CPU

MACIX Bus

PCI Bus

StrongARMME

ME

ME

ME

ME

ME

• IXP 1200• StrongARM @

233MHz• Microengine(6)

• IXP 2400• Xscale @

700MHz• Microengines(8)

Our Design

Using TCP Splicing

Results

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