Transcript CoDeeN + DNS = CoDNS

CoDeeN + DNS = CoDNS
Vivek Pai, Larry Peterson,
& the CoDeeN group
Princeton University
Origins of CoDNS
CoDeeN = Open CDN on PlanetLab
40 nodes, 4+ months, 24/7 operation
 Approaching 2 million reqs/day
 Extensive node monitoring
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Reliability by avoiding bad nodes
Reliability at lower layers = delays
 Delays = annoyed users
 Better to avoid slow peers
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Types of Unreliability
Dead nodes
High application-level packet losses
Resource exhaustion (FDs, disk)
DNS
DNS?
 Yes, DNS
 Lookup of origin server on cache misses
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DNS Problems
Sometimes a major cause of slowdowns
May not be node-local failure
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Other resources salvageable
Fix may help other non-CDN services
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DNS as a “utility”
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DNS-Related Avoidance
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Insight
Use content distribution infrastructure to
mask DNS resolver failures
If local DNS lookups failing
Send to a nearby, working node
 Use locality, load balancing to avoid
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Prototype
In place on all CoDeeN nodes
Currently using custom infrastructure
 Will soon share CoDeeN infrastructure

Tries to be intelligent
Immediate remote lookup on persistent
local failure
 Backoff-based delay otherwise
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Cornell – Regular Problems
Time & “Failures”, regular DNS
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Cornell – Regular Problems
Lookup times – DNS & CoDNS
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CMU – Cron Jobs?
Time & Failures, regular DNS
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CMU – Cron Jobs?
Lookup times – DNS & CoDNS
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GaTech “Disappearance”
Time & Failures, regular DNS
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GaTech “Disappearance”
Time & Failures, regular CoDNS
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UCLA – Failure Burst
Lookup times – DNS & CoDNS
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Summary
DNS failures fairly widespread
CoDNS prototype very promising
Additional overhead very tolerable
Working on standalone deployment
Will listen on port 53, do the right thing
 Goal: general PlanetLab service
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