Availability in WideArea Service Composition

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Availability in Wide-Area Service Composition

• Bhaskaran Raman and Randy H. Katz
• SAHARA, EECS, U.C.Berkeley

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Problem Statement
Poor availability of wide-area (inter-domain)
Internet paths
Labovitz, FTCS99
BGP recovery can take several 10s of seconds
Labovitz, SIGCOMM00
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Architecture
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Failure detection in the Wide-Area

• Two important characteristics
• Distbn. of outage periods
• Rate of occurrence
• Wide-Area traces
• 12 pairs of hosts Berkeley, Stanford, UIUC, CMU,
  TU-Berlin, UNSW
• 300ms heart-beat

• Approx. 2sec timeout
• Low rate of occurrence (once an hour)
• Good for many real-time applications

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Key Design Points

• Overlay size how many nodes?
• A comparison Akamai cache servers
• O(10,000) servers for Internet-wide operation
• Probably a lesser number of data-center locations
• Link-state floods
• Twice for each failure
• For a 1,000-node graph estimate edges 10,000
• Failures (gt1.8 sec outage) O(once an hour) in
  the worst case
• Only about 6 floods/second in the entire network!
• Graph computation
• Modified version of Dijkstras for service
  composition
• O(kElog(N)) computation time k services
  composed
• For 6,510-node network, this takes 50ms
• Huge overhead, but path caching helps
• Memory a few MB

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Wide-Area experiments setup

• 8 nodes
• Berkeley, Stanford, UCSD, CMU
• Cable modem (Berkeley)
• DSL (San Francisco)
• UNSW (Australia), TU-Berlin (Germany)
• Text-to-speech composed sessions
• Half with destinations at Berkeley, CMU
• Half with recovery algo enabled, other half
  disabled
• 4 paths in system at any time
• Duration of session 2min 30sec
• Run for 4 days
• Metric loss-rate measured in 5sec intervals

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Loss-rate for a pair of paths
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CDF of loss-rates of all paths failed
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CDF of gaps seen at client
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Summary

• Failure detection makes sense in 2sec
• Improvement in availability for real-time
  applications
• Text-to-speech composed application
• About 3.5-4 sec recovery time
• 2,000ms failure detection timeout
• 1,000ms recovery signaling
• 500-1,000ms state restoration (re-process current
  text sentence)
• Of the 2,872 paths, 18 were recovered (0.63)
• Availability Number of 5sec periods with gt10
  outage
• Other issues stability, scaling, load-balancing
• Studied using Millennium emulation platform