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OSDI 2002 Boston, MA 1 The Effectiveness of Request Redirection on CDN Robustness Limin Wang Vivek Pai and Larry Peterson Princeton University.

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Presentation on theme: "OSDI 2002 Boston, MA 1 The Effectiveness of Request Redirection on CDN Robustness Limin Wang Vivek Pai and Larry Peterson Princeton University."— Presentation transcript:

1 OSDI 2002 Boston, MA 1 The Effectiveness of Request Redirection on CDN Robustness Limin Wang Vivek Pai and Larry Peterson Princeton University

2 December 11, 20025 th OSDI, Boston, MA2 Motivation Server infrastructure critical Failures are noticeable Consequences are serious CDNs are commonly used Robust service under heavy load News items, flash crowds Overload-style attacks (DDoS) We can exploit CDNs for this

3 December 11, 20025 th OSDI, Boston, MA3 BBB.COM WWW Service client

4 December 11, 20025 th OSDI, Boston, MA4 Content Distribution Networks BBB.COM client server surrogate B B B B B B cache A A A A A A AAA.COM C C C C C C CCC.COM redirector

5 December 11, 20025 th OSDI, Boston, MA5 Partial Replication on CDN BBB.COM client server surrogate B B B B A A A A AAA.COM C C C BB A A C C C CCC.COM redirector

6 December 11, 20025 th OSDI, Boston, MA6 Partial Replication on CDN BBB.COM client server surrogate B B B B A A A A AAA.COM C C C C CCC.COM redirector

7 December 11, 20025 th OSDI, Boston, MA7 Factors Affecting Redirection Goals Increase system throughput under load Reduce response latency perceived by clients Server load Pick least loaded server Network proximity Pick closest server Cache locality Pick server just served the object What’s the tradeoff across different loads? Often conflict

8 December 11, 20025 th OSDI, Boston, MA8 Contributions New Class of CDN Redirection Strategies: Fine Dynamic Replication (FDR) Selectively replicates URLs Balances load, locality, bandwidth and proximity 60-91% throughput improvement Deters DDoS, absorbs flash crowds naturally New Hybrid Simulator: NS-2 + LogSim End-to-end — from SYN to sync() Large scale simulations 128 servers, 1000+ clients, ~70,000 req/sec

9 December 11, 20025 th OSDI, Boston, MA9 Outline Motivation and Contributions Design Space of Redirection Strategies Evaluation Methodology Experimental Results Conclusions and Ongoing Work

10 December 11, 20025 th OSDI, Boston, MA10 Redirection Decision Dimensions URL Hashing – decentralized, coherent Different hashing schemes Replication More replicas  closer replicas Too many replicas  working set overload Load knowledge How accurate?

11 December 11, 20025 th OSDI, Boston, MA11 Background: Hashing Algorithms Consistent Hashing (CHash) hash(svr1), … hash(svrN) hash(URL) select “closest” server Highest Random Weight (HRW) hash(URL, svr1), … hash(URL, svrN) sort hash values, get ordered server list select server with highest hash value

12 December 11, 20025 th OSDI, Boston, MA12 Strategies: Random Random (Rand) Requests randomly sent to surrogates Baseline case Assumes no pathological behavior

13 December 11, 20025 th OSDI, Boston, MA13 Strategies: Static Replication Replicated Consistent Hashing (R-CHash) Each URL hashed to a fixed # of replicas For each request, randomly selects one replica Similar to Karger’s Consistent Hashing paper Replicated Highest Random Weight (R-HRW) Similar to R-CHash, but use HRW hashing Minimizes two URLs having same set of replicas Approximates best published CDN algorithms Improve locality over Random

14 December 11, 20025 th OSDI, Boston, MA14 Strategies: Static + Load Load-Aware Static Replication (fine grained) LR-CHash Estimates server load at redirectors Picks up least-loaded server from server set LR-HRW Counterpart of LR-CHash Approximates CDN’s best load balancing behavior

15 December 11, 20025 th OSDI, Boston, MA15 Strategies: Dynamic Replication (New) Coarse Dynamic Replication (CDR) HRW hashing  ordered server list Walks list to find acceptably loaded server # of replicas based on server load (estimated locally) Fine Dynamic Replication (FDR) # of replicas based on URL popularity, too FDR-Global, reference scheme with global load info Dynamically balance load and locality

16 December 11, 20025 th OSDI, Boston, MA16 Summary of Strategies CategoryStrategy Hashing SchemeDynamic Server set? Load aware? CHashHRW Random Static R-CHash R-HRW Static +Load LR-CHash LR-HRW Dynamic CDR FDR Network Proximity NPR-CHash NPLR-CHash NP-FDR

17 December 11, 20025 th OSDI, Boston, MA17 Evaluation Methodology Simulations Merge NS-2 and LogSim SYN to sync(), in detail Work Load Normal load 1000 clients replaying Rice Trace Flash crowds 10-80% of 1000 clients hitting 10 URLs Rest clients replaying Rice Trace

18 December 11, 20025 th OSDI, Boston, MA18 Simulation: Topology – Server, – Client, – Router SC R 128 servers, 1000 clients

19 December 11, 20025 th OSDI, Boston, MA19 Capacity: Normal Load (64 svrs, 1000 clnts) Static Static + Load Dynamic

20 December 11, 20025 th OSDI, Boston, MA20 Latency Measurement Points Static Static + Load Dynamic

21 December 11, 20025 th OSDI, Boston, MA21 Latency: Normal Load, (64 svrs, 1000 clnts) Random Max:9.3K req/s

22 December 11, 20025 th OSDI, Boston, MA22 Latency: Normal Load, (64 svrs, 1000 clnts) Static+Load (LR-HRW) Max: 25.4K req/s

23 December 11, 20025 th OSDI, Boston, MA23 Handle Tail Separately ( 99% file  530KB ) Static+Load (LR-HRW) Max: 25.4K req/s

24 December 11, 20025 th OSDI, Boston, MA24 Server Resource Utilization (64 svrs) Utilization Scheme Max Thpt (Kreq/s) DISK(%)CPU(%) MeanStddevMeanStddev Random9.3100.00.0021.031.36 R-CHash20.499.153.8957.8818.36 R-HRW18.599.741.2647.8815.33 LR-CHash25.497.8312.5159.4818.85 LR-HRW25.499.005.9458.4316.56 CDR32.636.1025.1890.0711.78 FDR33.233.9620.3893.867.58 FDR-Global33.217.6015.4391.9311.81 Under Normal Work Load at Individual Maximum Capacity

25 December 11, 20025 th OSDI, Boston, MA25 Conclusions New dynamic schemes work best 60-91% improvement versus standard CDN Without sacrificing latencies Scale well, successful attacks more difficult Bottleneck shifts from Disk to CPU/Network Desired – shows selective replication works More results in the paper Normal workloads, flash crowd/DDoS traffic Network Proximity and Heterogeneity Large file effects

26 December 11, 20025 th OSDI, Boston, MA26 Ongoing Work PlanetLab deployment (CoDeeN networks) Intel-funded overlay network, academic testing CDN Currently running on 12 sites using proxy servers Early stage, many more to do Traffic monitoring, capacity test, server management … More simulations Larger scale, faster simulated servers More topologies (power-law, etc) More traces, more elaborate client request model

27 December 11, 20025 th OSDI, Boston, MA27 Thank you! For More Information http://www.cs.princeton.edu/nsg/cdn Acknowledgements HP/Compaq/Intel AlphaServer ES-40, 8GB RAM rx4610 Server, Itanium, 16GB RAM iMimic DataReactor Proxy Servers

28 December 11, 20025 th OSDI, Boston, MA28 Capacity Scalability Normal Load, 1000 normal clients

29 December 11, 20025 th OSDI, Boston, MA29 Various Flash Crowds (32 servers) 1 victim file, 1KB10 victim files, avg 6KB

30 December 11, 20025 th OSDI, Boston, MA30 Capacity: Flash Crowd, 64 Servers 750 normal clients, 250 intensive clients Static Static + Load Dynamic

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