Mechanisms for Quality of Service in Web Clusters

1. Terena Networking Conference - TNC2001 Mechanisms for Quality of Service in Web Clusters M. Colajanni University of Modena V. Cardellini, E. Casalicchio, S.Tucci University of Roma “Tor Vergata” Speaker: Emiliano Casalicchio ecasalicchio@ing.uniroma2.it http://www.ce.uniroma2.it/people/casali Additional Info: www.ce.uniroma2.it

2. Outline • Motivations • Quality of Service & Quality of Web Services • System architecture • QoS-blind vs. QoS-aware dispatching algorithms • Results • System and workload model • Performance metrics • Simulation results • Summary Terena Networking Conference - TNC2001

3. Why QoS in Web services? • The second generation of Web sites • communication channel for critical information • fundamental technology for information systems of the most advanced companies and organizations • business-oriented media • The new Web requires • differentiation of users and services • supports to heterogeneous applications and user expectations • differentiated pricing for content hosting and service providing Terena Networking Conference - TNC2001

4. A Web cluster architecture for high performance Web services • IBM TCP Router • CISCO Local Director • IBM NetDispatcher • Foundry Networks’ ServerIron family • CISCO HP WebQoS Local Director Terena Networking Conference - TNC2001

5. Quality of Web Services (QoWS) High performance systems  Systems for Quality of Service • QoS principles and mechanisms have been deeply studied in the computer network area, but • QoS principles are not immediately applicable to the server side of the Web System • Network QoS and server QoWS principles must be combined to provide a peer-to-peer QoS for Web services The focus of this talk will be on QoWS for Web clusters Terena Networking Conference - TNC2001

6. QoWS From QoS to QoWS in Web clusters • To define QoWS principles we need to find out • feasible mechanisms to achieve QoWS • Web Cluster components that can implement the QoWS principles and mechanisms Our idea: starting from main QoS principles • classification • performance isolation • high resource utilization • request admission control Terena Networking Conference - TNC2001

7. QoWS principles • Classification(at layer-4/7 Web Switch) • clients and services classification • users identification • Performance isolation • queuing scheduling policies (at Web server: CPU,disk,…) • resource partitioning (at the Web server for fine-grain level, at the Web Switch for coarse-grain level) • High resource utilization (at Web switch/server) • dynamic resource partitioning • Request admission (at Web switch/server) • estimation of resource need (at Web switch) • access control mechanism (at Web switch/server) Terena Networking Conference - TNC2001

8. A QoWS-enabled Web cluster architecture Terena Networking Conference - TNC2001

9. QoS-blind dispatching algorithms • Round-Robin (RR) • Least-Loaded server (LL) • Weighted Round-Robin (WRR) • Server Admission with priority (SerADM-SerPRI) Terena Networking Conference - TNC2001

10. QoS-aware dispatching algorithms • without partitioning of Web servers • Switch Admission (SwiADM) • Switch Admission with server priority (SwiADM-SerPRI) • with partitioning of Web servers • Dynamic partition of servers (Partition) Terena Networking Conference - TNC2001

11. Classification Perf.Isolation High Res.Util. Req.Adm SerADM-SerPRI SwiADM SwiADM-SerPRI Partition Yes YesNoYes YesNo NoYes Yes YesNoYes Yes Yes Yes Yes QoS-aware algorithms Terena Networking Conference - TNC2001

12. Number of servers Disk parameter Memory transfer rate Intra-server bandwidth 10 20 MBps, 7200 RPM, 0.05 msec c.d., 9 msec s.t. 100 MBps 100 Mbps switched LAN Arrival rate Requests per session User think time Embedded objects Hit size - body Hit size - tail 100 - 500 clients per second (300cps) Inverse Gaussian (  = 3.86,  = 9.46 ) Pareto (  = 1.4, k = 2) Pareto (  = 1.33, k = 1) Lognormal (  = 7.640,  = 1.705 ) Pareto (  = 1.383, k = 2924) Service Classes High (30%) - Medium (26.5%) - Low (43.5%) System and workload model Value (default) Parameter Terena Networking Conference - TNC2001

13. Performance metrics • 90-percentile of page delay • measure the completion time of a Web page at the Web cluster side • the X-percentile is used to define the Service Level Agreement (SLA) for predictive services • Percentage of dropped requests • measure the percentage of users that perceive a deny of service Terena Networking Conference - TNC2001

14. Simulation results (1) Terena Networking Conference - TNC2001

15. Simulation results (2) Terena Networking Conference - TNC2001

16. Conclusions • Basic requirements for QoWS are satisfied by policies that integrate main mechanisms for network-QoS into main components of a Web cluster (i.e., Web servers and/or Web switch): • priority scheduling • dynamic server partitioning • admission control Terena Networking Conference - TNC2001

17. Work in progress • Level-7 Web switch with QoS-enabled policies • New policies for dynamic request partitioning • Prototype implementation Additional information: www.ce.uniroma2.it Terena Networking Conference - TNC2001