1. Vivek Pai, Larry Peterson, & the CoDeeN group Princeton University
CoDeeN + DNS = CoDNS
Vivek Pai, Larry Peterson,
& the CoDeeN group
Princeton University

2. Origins of CoDNS CoDeeN = Open CDN on PlanetLab
40 nodes, 4+ months, 24/7 operation
Approaching 2 million reqs/day
Extensive node monitoring
Reliability by avoiding bad nodes
Reliability at lower layers = delays
Delays = annoyed users
Better to avoid slow peers
Oct 19, 2003
RPI PlanetLab Meeting

3. Oct 19, 2003
RPI PlanetLab Meeting

4. 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
Oct 19, 2003
RPI PlanetLab Meeting

5. DNS Problems Sometimes a major cause of slowdowns
May not be node-local failure
Other resources salvageable
Fix may help other non-CDN services
DNS as a “utility”
Oct 19, 2003
RPI PlanetLab Meeting

6. DNS-Related Avoidance
Oct 19, 2003
RPI PlanetLab Meeting

7. 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
Oct 19, 2003
RPI PlanetLab Meeting

8. Prototype In place on all CoDeeN nodes Tries to be intelligent
Currently using custom infrastructure
Will soon share CoDeeN infrastructure
Tries to be intelligent
Immediate remote lookup on persistent local failure
Backoff-based delay otherwise
Oct 19, 2003
RPI PlanetLab Meeting

9. Cornell – Regular Problems
Time & “Failures”, regular DNS
Oct 19, 2003
RPI PlanetLab Meeting

10. Cornell – Regular Problems
Lookup times – DNS & CoDNS
Oct 19, 2003
RPI PlanetLab Meeting

11. CMU – Cron Jobs? Time & Failures, regular DNS Oct 19, 2003
RPI PlanetLab Meeting

12. CMU – Cron Jobs? Lookup times – DNS & CoDNS Oct 19, 2003
RPI PlanetLab Meeting

13. GaTech “Disappearance”
Time & Failures, regular DNS
Oct 19, 2003
RPI PlanetLab Meeting

14. GaTech “Disappearance”
Time & Failures, regular CoDNS
Oct 19, 2003
RPI PlanetLab Meeting

15. UCLA – Failure Burst Lookup times – DNS & CoDNS Oct 19, 2003
RPI PlanetLab Meeting

16. 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
Oct 19, 2003
RPI PlanetLab Meeting