How LinkedIn used TCP Anycast to make the site faster
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TCP anycast effectiveness in public internet and measurement by real user monitoring (RUM) to improve user experience,
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How LinkedIn used TCP Anycast to make the site faster
- 2. How LinkedIn used TCP Anycast to make the site faster Ritesh Maheshwari Shawn Zandi
- 3. Anycast • Anycast provides a distributed service via rou8ng. • It is not really different than unicast. • NLRI object with mul8ple next-‐hops. • It simply works for both TCP and UDP applica8ons. (use with cau8ons!)
- 4. SF CHI NYC Bob www.linkedin.com 2001:db8::1/56 www.linkedin.com 2001:db8::1/56 www.linkedin.com 2001:db8::1/56
- 5. Anycast with ECMP • Not a real issue in today’s internet • Consistent flow rou8ng is required (per packet load balancing breaks Anycast) – Pre_y Much Standard • Most BGP implementa8ons do not load balance across different AS-‐PATHs even with same size.
- 6. Anycast Complica8ons • Broken MTU Challenges • ICMP message may not reach the intended receiver to report MTU problem. Adjus8ng MSS can help. • RPF Checks • Mul8ple covering prefixes -‐ Only one Service Address should be covered by each adver8sed prefix /24 or /56 • Monitoring!
- 7. But! How to measure Anycast effec8veness?
- 8. What is RUM? JavaScript (Client-‐code) to measure performance • DNS Time • Connec8on 8me • First Byte Time • Download Time • Page Load Time
- 9. What are PoPs? Point of Presence / PoP • Small-‐scale data centers • Proxy servers at LinkedIn (ATS)
- 10. Without PoPs Browser Data Center connec8on 8me 250ms
- 11. Without PoPs Browser Data Center connec8on 8me server compute 8me 250ms 500ms
- 12. Without PoPs Browser Data Center connec8on 8me 3-‐5 round trips first byte 8me + page download 8me 5 RTTs = 5x250ms = 1250ms server compute 8me 250ms Total = 2000ms 500ms
- 13. With PoPs Browser Data Center PoP 100ms 250ms
- 14. With PoPs Browser Data Center PoP 100ms connec8on 8me Old TCP Connec8on
- 15. With PoPs Browser Data Center PoP 100ms connec8on 8me one round trip first byte 8me + page download 8me Old TCP Connec8on server compute 8me 500ms
- 16. With PoPs Browser Data Center PoP 100ms connec8on 8me one round trip 5 RTTs = 5x100ms = 500ms Total = 1100ms 900 ms gain! first byte 8me + page download 8me Old TCP Connec8on 500ms server compute 8me
- 17. How are users assigned to PoPs? Through DNS: IP handed based on user’s resolver country # Spain $ dig @109.69.8.51 +short www.linkedin.com 91.225.248.80 # California $ dig +short www.linkedin.com 216.52.242.80
- 18. Should India connect to Singapore or Dublin? How to assure op,mal PoPs assignment?
- 19. RUM beacons Fetch a 8ny object from each candidate PoP For each pop_name, 1. Start timer 2. Fetch {pop_name}.perf.linkedin.com/pop/admin 3. Stop timer Send data back to our servers • Millions of agents! • Analyze data to find “op8mal” PoP per country
- 20. We can assign countries to new PoPs! Country PoP Median Beacon Time(ms) China Hong Kong 434 China Dublin 1216 China Singapore 515 India Hong Kong 1368 India Dublin 1042 India Singapore 898
- 21. We can audit current assignment! Country Is PoP op8mal? Current PoP Op8mal PoP India TRUE Singapore Singapore Pakistan FALSE Singapore Dublin Spain TRUE Dublin Dublin Brazil FALSE US West Coast US East Coast Netherlands TRUE Dublin Dublin UAE FALSE US West Coast Dublin Italy TRUE Dublin Dublin Mexico TRUE US West Coast US West Coast Russia FALSE US West Coast Dublin
- 22. 0% 5% 10% 15% 20% 25% 30% India Pakistan Singapore Russia Brazil Percentage Improvement LinkedIn Homepage Download Time Improvement Median Improvement 90th Percen8le Improvement
- 25. Plot Twist: Assignment far from op8mal • About 31% of US traffic gets assigned to a subop8mal PoP. – 45% of East Coast • About 10% of traffic globally gets assigned to a subop8mal PoP.
- 26. DNS PoP assignment is subop8mal • Assignment based on Resolver IP, not Client IP DNS Resolver PoP US East PoP US West New York California
- 27. DNS PoP assignment is subop8mal • Assignment based on Resolver IP, not Client IP • Bad IP to Geo databases – Resolver really in NY, but database says CA
- 28. Story so far 1. We built PoPs 2. …used RUM to assign users to Op8mal PoPs 3. …found DNS based assignment is subop8mal
- 29. Accurate PoP assignment Problem • Bug our DNS providers (31% -‐> 27%) • Run our own DNS How about Anycast?
- 30. Anycast – One IP, Mul8ple Servers PoP A PoP B PoP C Bob 1.1.1.1 1.1.1.1 1.1.1.1 ü Client IP, not Resolver IP used! ü No Geo-‐IP Databases
- 31. How does Anycast compare to DNS? Will anycast send more users to op,mal PoP? Ø Lets test it!
- 32. RUM to rescue For each PoP: 1. Announce same anycast IP (108.174.13.10) 2. Configure a domain ac.perf.linkedin.com to point to 108.174.13.10
- 33. RUM to rescue For each page view: 1. RUM downloads a 8ny object : ac.perf.linkedin.com/pop/admin 2. Read X-Li-Pop response header to record which PoP served the object 3. Send this back to LinkedIn with RUM data Data: 1. For each user, the anycast PoP 2. For each user, the op8mal PoP (from pop beacons)
- 34. Results J Region or Country DNS % Op8mal Assignment Anycast % Op8mal Assignment Illinois 70 90 Florida 73 95 Georgia 75 93 Pennsylvania 85 95
- 35. Results L Region or Country DNS % Op8mal Assignment Anycast % Op8mal Assignment Arizona 60 39 Brazil 88 33 New York 77 74
- 37. Fewer hops != Lower Latency • Carriers prefer to haul packets within their own network • Peering can create inter-‐con8nental short cuts Z X Alice Y inter-‐con8nental link 1.1.1.1 1.1.1.1 1.1.1.1
- 38. Maybe DNS wasn’t so bad Con8nent-‐level assignments City / State level assignments
- 39. “Regional” Anycast DNS-‐based 1 anycast IP per con8nent Ran a RUM experiment, all was fine Z X Alice Y 2.2.2.2 1.1.1.1 1.1.1.1 inter-‐con8nental link
- 40. USA Ramp Results 50.00 55.00 60.00 65.00 70.00 75.00 80.00 85.00 90.00 95.00 100.00 20141207 20141208 20141209 20141210 20141211 20141212 20141213 20141214 20141215 20141216 20141217 % Traffic going to Op8mal PoP Date Illinois Florida North Carolina Indiana NY NJ VA WV LA Ramp outside USA In progress
- 41. Story so far 1. We built PoPs 2. …used RUM to assign users to Op8mal PoPs 3. …found DNS based assignment is subop8mal 4. …evaluated Anycast as a solu8on using RUM 5. …now using Anycast to assign users to PoPs Next play: • Build more PoPs!
- 42. Story: The End Learnings • Clients are your measurement agents • Trust, but verify • You can have a bigger impact if you collaborate Next Play • Keep evalua8ng Anycast • Keep building new PoPs
- 43. ©2014 LinkedIn Corporation. All Rights Reserved.©2014 LinkedIn Corporation. All Rights Reserved.