Thomas Dreibholz Institute for Experimental Mathematics University of Duisburg-Essen, Germany University of Duisburg-Essen, Institute for Experimental Mathematics A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 2 Table of Contents What is Reliable Server Pooling?  Prototype Demonstration  Terminology and Protocols  Motivation and Application Scenarios The Challenge on Network Delay on Server Selection The Least Used with Degradation Policy Evaluation Conclusion and Outlook Thomas Dreibholz's Reliable Server Pooling Page Thomas Dreibholz's Reliable Server Pooling Page

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 3 What is „Reliable Server Pooling“? Prototype Demonstration

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 4 Reliable Server Pooling (RSerPool) Terminology:  Pool Element (PE):Server  Pool:Set of PEs  PE ID:ID of a PE in a pool  Pool Handle:Unique pool ID  Handlespace:Set of pools  Pool Registrar (PR)  Pool User (PU):Client  Support for Existing Applications Proxy Pool User (PPU) Proxy Pool Element (PPE) Protocols:  ASAP (Aggregate Server Access Protocol)  ENRP (Endpoint Handlespace Redundancy Protocol)

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 5 What is a Pool Policy?  A rule for the selection of the PEs  Defined in our IETF Working Group draft (draft-ietf-rserpool-policies-07.txt) Application of Policies  Registrar: Creates PE list upon request by PU  Pool User: Selection of a PE from the list  Both according to the pool policies (pool-specific!) Non-Adaptive Policies  Stateless: Random (RAND)  Stateful: Round Robin (RR)(Default policy, must be supported) Adaptive Policy  Least Used (LU) Load definition is application-specific! Round robin among multiple least-loaded PEs Server Selection Rules (Pool Policies)

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 6 The Challenge of Network Delay on Server Selection Challenge of Least Used  Load states get out of date, due to Network latency Cache Solution: Least Used with Degradation (LUD)  Policy Information: Load = Current Load (obvious) Load Increment = How much is load increased by a new request?  Select PE, which has lowest sum of (Load + Load Increment)  Round robin among equal-valued PEs  Upon selection: Increment load by load increment Incrementation only local on selection component (i.e. registrar and PU's cache)!  Upon update: Load is reset to latest known load state

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 7 The Application Model Server –PE Capacity –Shared among sessions (multi-tasking principle) Client –Requests are generated Request Size (effort) Request Interval (frequency) –Waiting queue for requests –Sequential processing System Utilization –PU:PE Ratio –Provisioning for certain Target Utilization, e.g. 80%

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 8 Performance Metrics Provider's Perspective “Does my server capacity gain revenue?” Average Utilization of server resources [%] User's Perspective “How much time is needed to process my requests?”  Avg. Handling Speed [% of average server capacity]  Depends on: Queuing Startup Server

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 9 Increasing the Network Delay - A Proof of Concept Example setup as a proof of concept Network latency reduces the handling speed but with LUD, there is a significant speed benefit compared to LU More investigations necessary  Workload parameters  Number of registrars  Cache Handling Speed

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 10 Variation of Workload Parameters: PU:PE Ratio Small PU:PE ratio is critical (high per-PU workload) LUD achieves significant performance improvement over LU Handling Speed Utilization LU, Req.Int=10s (critical!)

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 11 Variation of Workload Parameters: Request Interval Small request interval is critical (especially for small PU:PE ratio!) For PU:PE ratio > 1, LUD again achieves a significant improvement Handling Speed Utilization

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 12 Increasing the Number of Registrars Handlespace synchronization  Necessary to cope with PR failures  Additional load update latency Results:  LUD again achieves a significant benefit over LU... ... for realistic number of PRs (less than 10) Handling Speed

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 13 Using the PU-Side Cache Cache at the PU:  Stores partial, temporary subset of the handlespace  Reduces number of PR queries  Contents get out of date Results:  Again, LUD outperforms LU Handling Speed

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 14 Conclusion and Outlook Conclusion  RSerPool is the IETF's upcoming standard for service availability  Network delay leads to out-of-date load states for Least Used policy  Least Used with Degradation (LUD) Local increment upon selection, until update arrives Improved system performance, especially for critical workload parameter settings Future Work  From simulation to reality: Tests with our prototype implementation in the PlanetLab First results already available [KiVS2007]  Security analysis and robustness against DoS attacks

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 15 Thank You for Your Attention! Any Questions? Visit Our Project Homepage: Thomas Dreibholz, To be continued...

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 16 The RSerPool Protocol Stack Aggregate Server Access Protocol (ASAP)  PR  PE: Registration, Deregistration and Monitoring by Home-PR (PR-H)  PR  PU: Server Selection, Failure Reports Endpoint Handlespace Redundancy Protocol (ENRP)  PR  PR: Handlespace Synchronisation ASAP is IETF's first Session Layer standard! ASAP is IETF's first Session Layer standard!

Thomas Dreibholz A New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 17 Motivation Motivation of RSerPool:  Unified, application-independent solution for service availability  Not available before => Foundation of the IETF RSerPool Working Group Application Scenarios for RSerPool:  Main motivation: Telephone Signalling (SS7) over IP  Under discussion by the IETF: Load Balancing Voice over IP (VoIP) with SIP IP Flow Information Export (IPFIX) ... and many more! Requirements for RSerPool:  “Lightweight” (low resource requirements, e.g. embedded devices!)  Real-Time (quick failover)  Scalability (e.g. to large (corporate) networks)  Extensibility (e.g. by new server selection rules)  Simple (automatic configuration: “just turn on, and it works!”)