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Thomas DreibholzInstitute for Experimental Mathematics
University of Duisburg-Essen, Germany
University of Duisburg-Essen, Institute for Experimental Mathematics
A New Server Selection Strategyfor Reliable Server Pooling in Widely
Distributed Environments
Thomas DreibholzA 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 Pagehttp://tdrwww.iem.uni-due.de/dreibholz/rserpool/
Thomas Dreibholz's Reliable Server Pooling Pagehttp://tdrwww.iem.uni-due.de/dreibholz/rserpool/
Thomas DreibholzA New Server Selection Strategy for Reliable Server Pooling in Widely Distributed Environments P. 3
What is „Reliable Server Pooling“?Prototype Demonstration
Thomas DreibholzA 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 DreibholzA 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 DreibholzA 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Challenge of Least Used Load states get out of date, due to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 DreibholzA 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%
yAvgCapacitrvalRquestInte
RquestSize
opuToPERatiizationsystemUtil *
Thomas DreibholzA 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 DreibholzA 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 SpeedHandling Speed
Thomas DreibholzA 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 SpeedHandling SpeedUtilizationUtilization
LU, Req.Int=10s (critical!)LU, Req.Int=10s (critical!)
Thomas DreibholzA 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 SpeedHandling SpeedUtilizationUtilization
Thomas DreibholzA 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 SpeedHandling Speed
Thomas DreibholzA 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 SpeedHandling Speed
Thomas DreibholzA 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 DreibholzA 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:http://tdrwww.iem.uni-due.de/dreibholz/rserpool/
Thomas Dreibholz, [email protected]
To be continued ...To be continued ...
Thomas DreibholzA 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 DreibholzA 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!”)