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Scalable Internet Servers and Load Balancing

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  • 1. Computer Networks 11/11/2009 Internet Online Applications Scalable Internet Servers and Load Balancingg  Internet online applications  Applications accessible to online users through Internet Internet.  Examples  Online keyword search engine: Google.  Web email: Gmail.  News: CNN, NBC news. Web directory: Yahoo!, MSN. Kai Shen   Scalability requirements  Many simultaneous user accesses; large amount of hosted data, …  Internet servers  Computer systems that host these online applications 11/11/2009 CSC 257/457 - Fall 2009 1 11/11/2009 CSC 257/457 - Fall 2009 2 Internet Servers are at the Search Engine as An Example: Application Layer Step 1 – Crawling  Normally on the end hosts, involving no routers  Function on transport-layer protocols TCP/UDP  Crawling – get all these Web pages out there: g g p g  First retrieve some root pages;  Parse their content and follow hyperlinks to retrieve more pages;  Depth-first search or breadth-first search? Remove Internet duplicates. Google Yahoo! CNN 11/11/2009 CSC 257/457 - Fall 2009 3 11/11/2009 CSC 257/457 - Fall 2009 4 CSC 257/457 - Fall 2009 1
  • 2. Computer Networks 11/11/2009 Performance Analysis for Search Engine as An Example: Crawling Step 2 – Indexing  What are the resources involved?  CPU processing for TCP/HTTP protocol handling and the p g p g  Indexing parsing of page content f  crawled raw web pages are not easy to search.  writing to disk storage  we index them to formats that are easy to search. network bandwidth to remote web sites As part of indexing, we need to give each page an ID    Assume average page size 10KB  using a hash function. raw processing power of a single CPU ……   1000 requests/sec Computer: Page #123 Page #357  I/O to a single disk  100 seeks/sec  up to 100 requests/sec  network bandwidth from/to the Internet  T1 link (1.5Mbit/s)  12 requests/sec Networks: Page #124 Page #468 ……  T3 link (45Mbit/s)  360 requests/sec 11/11/2009 CSC 257/457 - Fall 2009 5 11/11/2009 CSC 257/457 - Fall 2009 6 Search Engine as An Example: Step 3 – Online Search Partitioning and Replication Index servers (partition 1) Index server Firewall/ Firewall Router Local- Local-area network Web server/ Query handler Local- Local-area Internet Internet network Index servers (partition 2) Page server Web server/ Query handlers Page servers Scalability, reliability 11/11/2009 CSC 257/457 - Fall 2009 7 11/11/2009 CSC 257/457 - Fall 2009 8 CSC 257/457 - Fall 2009 2
  • 3. Computer Networks 11/11/2009 Load Balancing on Internet Servers Load Balancing over Internet Technique 1 - DNS Rotation Servers 128.111.1.2  Popular sites like Google or CNN receive tens or hundreds of millions of hits per day day. IP address of CNN.com?  A large number of replicated servers are used at Firewall/ 128.111.1.3 these sites. Router IP address of  Key question: how to balance client requests over CNN.com? Internet these servers? 128.111.1.4 128.111.1.2 Web servers for CNN.com 128.111.1.3 DNS server for CNN.com 11/11/2009 CSC 257/457 - Fall 2009 9 11/11/2009 CSC 257/457 - Fall 2009 10 Load Balancing on Internet Servers Discussions on DNS Rotation Technique 2 – Cooperative Offloading 128.111.1.2  Advantages  Require almost no change on the existing Internet architecture Firewall/ 128.111.1.3 Router  Problems  DNS Caching Internet  Rigid load balancing policy  can’t balance based on runtime load changes 128.111.1.4  slow or no adjustment in response to failures Web servers for CNN.com 11/11/2009 CSC 257/457 - Fall 2009 11 11/11/2009 CSC 257/457 - Fall 2009 12 CSC 257/457 - Fall 2009 3
  • 4. Computer Networks 11/11/2009 Discussions on Cooperative Cooperative Offloading with Offloading TCP Handoff [Pai et al. ASPLOS1998] 128.111.1.2 What does 1.3 do?  Can be combined with the DNS rotation. What does 1.4 do?  Advantages:  More flexible policy is possible clt IP Firewall/ 128.111.1.3 Router  Be more responsive to runtime workload and server 1.3 failures (to a certain degree) clt IP Internet 1.4  Problems: 128.111.1.4  Need software changes on servers 1.3 13  Longer delay clt IP Web servers for CNN.com All packets in a TCP connection must offload to one server? 11/11/2009 CSC 257/457 - Fall 2009 13 11/11/2009 CSC 257/457 - Fall 2009 14 Cooperative Offloading vs. Load Balancing on Internet Servers TCP Handoff Technique 3 – Load Balancing Router 128.111.1.2 clt IP  Software changes on the servers g 1.2 1.2 clt IP clt IP Delays 128.111.1.3  Firewall 1.1 LB Router Internet 128.111.1.1 1.1 clt IP 128.111.1.4 Web servers for CNN.com 11/11/2009 CSC 257/457 - Fall 2009 15 11/11/2009 CSC 257/457 - Fall 2009 16 CSC 257/457 - Fall 2009 4
  • 5. Computer Networks 11/11/2009 More About Load Balancing Router Summary How deep do we look into the network protocol stack?  Scalable Internet servers  Network layer (IP)?  partitioning  replication  Transport layer (TCP/UDP)?  Application layer?  Load balancing for Internet servers  DNS rotation Load balancing policies in LB routers (Goal: transparency,  cooperative offloading (w. TCP handoff) plug-and-play)  Load balancing router  Simple rotation  Changes required on the components: components DNS server?? Least number of active requests    Web server??  Shortest response time  client??  router?? 11/11/2009 CSC 257/457 - Fall 2009 17 11/11/2009 CSC 257/457 - Fall 2009 18 CSC 257/457 - Fall 2009 5

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