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Healing the Web:An Overview of CoDeeN & Related Projects
Vivek Pai, Larry Peterson + many othersPrinceton University
Jan 30, 2006 - GENI visit 2
How This All Started
OSDI paper on Content Distribution Network (CDN) algorithms
NS-2 simulations on 8GB AlphaServerLimits of detailed simulation – 70 hrs per experiment, huge memory requirementsStill only 1% as large as real networks
PlanetLab developedSuddenly, can get real traffic
Jan 30, 2006 - GENI visit 3
Toward a Self-Healing Web
Goals:Improve all levels of Web infrastructureInteroperate where possibleDrive with real trafficFeed back measurements
Routing
Name Lookup
Data Transfer
Replication
Client
Jan 30, 2006 - GENI visit 4
Basic CoDeeN
CoDeeN Proxy
origin
RequestRespons
e
Cache hit
Each CoDeeN proxy is a forward proxy, reverse proxy, & redirector
Cache miss
Response
Cache hit
Cache missRespons
eRequest
Cache Miss
Data Transfer
Jan 30, 2006 - GENI visit 5
By The Numbers…
Running 24/7 since June 2003*Over 1 million unique IPs as clientsAbout 20 billion requests servicedOver 25 million reqs/day
Highest-request project on PlanetLab#2 in bytes/day – we serve smaller objs
*not including PlanetLab Dec 2003 upgrade
Data Transfer
Jan 30, 2006 - GENI visit 6
Wide Area Network(WAN)
CoDNS
CoDNS
My LAN
LAN
LDNSCoDNS
My Machine
LDNS
rem
ote
answ
er
ClientPrograms
rem
ote
query
Name Lookup
Jan 30, 2006 - GENI visit 7
AvailabilityAdds one ‘9’, from 99% to
99.9%
9%
90%
99%
99.9%
99.99%
0 10 20 30 40 50 60 70 80 90
Nodes Sorted By LDNS Availability
Availab
ilit
y(%
)
CoDNS
LDNS
Name Lookup
Jan 30, 2006 - GENI visit 8
Evaluation – Live Traffic
0
100
200
300
400
500
600
700
800
900
1000
0 10 20 30 40 50 60 70 80 90
Nodes Sorted by LDNS Response Time
Av
era
ge R
esp
on
se T
ime(m
s)
LDNS
CoDNS
Name Lookup
Jan 30, 2006 - GENI visit 9
CoBlitz
Agent CDNClient
CDN reverse caches the chunks!
CDN
CDNCDN
CDN ClientAgent
CDN
chunk1
chun
k1chunk2
chunk3
chunk2
chunk5
chunk5
chunk1
chunk1
chunk4 chunk4 chunk5
chun
k5
chunk1 chunk2
chunk3 chunk3
chunk4 chunk5
CDN = Redirector + Reverse Proxy
Replication
Jan 30, 2006 - GENI visit 10
0
0.5
1
1.5
2
2.5
3
3.5
Direct BitTorrent CoBlitz
Do
wn
load
Rat
e (M
bp
s) Slowest
Median
CoBlitz Performance
CoBlitz users:CiteSeer digital libraryFedora Core LinuxPlanetLab projects
Replication
Jan 30, 2006 - GENI visit 11
PlanetSeerHost service
CDN
Components Passive monitoring
Active probing
AdvantagesLow overhead
Wide coverage
Client
A
C
B
R1
R2
Routing
Jan 30, 2006 - GENI visit 12
Confirmed Anomaly BreakdownConfirmed anomalies
271,898 in 90 days2 per minute100x more
Temp loop 1%
Path Change 44%
Fwd Outage 9%
Other Outage 23%
Persist Loop 7%
Temp Anomalies 16%
Routing
Jan 30, 2006 - GENI visit 13
Going Forward
Cycles + bandwidth + latencyqualitatively change opportunities
Obvious gains: performance, capacity, storageByzantine-like protocols become feasibleMore time for reasoning – online failure detection, repair, recoveryDeeper analysis – better classifiers, boostingBetter security – more cycles needed for crypto, dynamic SSL