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Dependability in the Internet Era

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  1. Dependability in the Internet Era Jim Gray Microsoft Research High Dependability Computing Consortium Conference Santa Cruz, CA 7 May 2001 REVISED: 13 Feb 2005 Stanford, CA

  2. Outline • The glorious past (Availability Progress) • The dark ages (current scene) • Some recommendations

  3. Telephone Systems Computer Systems Internet Cell phones PreviewThe Last 10 Years: Availability Dark AgesReady for a Renaissance? • Things got better, then things got a lot worse! 99.999% 99.999% 99.99% Availability 99.9% 99% 9% 1950 1960 1970 1980 1990 2000 2010

  4. DEPENDABILITY: The 3 ITIES • RELIABILITY / INTEGRITY: Does the right thing.(also MTTF>>1) • AVAILABILITY: Does it now. (also 1 >> MTTR ) MTTF+MTTRSystem Availability:If 90% of terminals up & 99% of DB up?(=>89% of transactions are serviced on time). • Holistic vs. Reductionist view Security Integrity Reliability Availability

  5. Fail-Fast is Good, Repair is Needed Lifecycle of a module fail-fast gives short fault latency High Availability is low UN-Availability Unavailability ~ MTTR MTTF Improving either MTTR or MTTF gives benefit Simple redundancy does not help much.

  6. Fault Model • Failures are independentSo, single fault tolerance is a big win • Hardware fails fast (dead disk, blue-screen) • Software fails-fast (or goes to sleep) • Software often repaired by reboot: • Heisenbugs • Operations tasks: major source of outage • Utility operations • Software upgrades

  7. Disks (raid) the BIG Success Story • Duplex or Parity: masks faults • Disks @ 1M hours (~100 years) • But • controllers fail and • have 1,000s of disks. • Duplexing or parity, and dual path gives “perfect disks” • Wal-Mart never lost a byte (thousands of disks, hundreds of failures). • Only software/operations mistakes are left.

  8. Fault Tolerance vs Disaster Tolerance • Fault-Tolerance: mask local faults • RAID disks • Uninterruptible Power Supplies • Cluster Failover • Disaster Tolerance: masks site failures • Protects against fire, flood, sabotage,.. • Also, software changes, site moves,… • Redundant system and service at remote site.

  9. 9 9 9 9 9 Availability Un-managed Availability well-managed nodes Masks some hardware failures well-managed packs & clones Masks hardware failures, Operations tasks (e.g. software upgrades) Masks some software failures well-managed GeoPlex Masks site failures (power, network, fire, move,…) Masks some operations failures

  10. Case Study - Japan"Survey on Computer Security", Japan Info Dev Corp., March 1986. (trans: Eiichi Watanabe). Vendor Vendor (hardware and software) 5 Months Application software 9 Months Communications lines 1.5 Years Operations 2 Years Environment 2 Years 10 Weeks 1,383 institutions reported (6/84 - 7/85) 7,517 outages, MTTF ~ 10 weeks, avg duration ~ 90 MINUTES To Get 10 Year MTTF, Must Attack All These Areas 4 2 % Tele Comm lines 1 2 % 1 1 . 2 Environment % 2 5 % Application Software 9 . 3 % Operations

  11. Case Studies - Tandem Trends MTTF improved Shift from Hardware & Maintenance to from 50% to 10% to Software (62%) & Operations (15%) NOTE: Systematic under-reporting of Environment Operations errors Application Software

  12. Dependability Status circa 1995 • ~4-year MTTF • 5 9s for well-managed sys. Fault Tolerance Works. • Hardware is GREAT (maintenance and MTTF). • Software masks most hardware faults. • Many hidden software outages in operations: • New Software. • Utilities. • Need to make all hardware/software changes ONLINE. • Software seems to define a 30-year MTTF ceiling. • Reasonable Goal: 100-year MTTF. class 4 today=>class 6 tomorrow.

  13. Honorable Mention • The nice folks at Tandem (now HP)) • Made failover fast (30 seconds or less). • Made change online • Add hardware/software • Reorganize database. • Rolling upgrades. • Added at least one 9 to their story.

  14. And Then? • Hardware got better (& more complex) • Software got better (& more complex) • Raid is standard, Snapshots becoming standard • Cluster in a box: commodity failover • Remote replication is standard.

  15. Outline • The glorious past (Availability Progress) • The dark ages (current scene) • Some recommendations

  16. Telephone Systems Computer Systems Internet Cell phones Progress? • MTTF improved from 1950-1995 • MTTR incremental improvements 1970 --- failover • Hardware and Software online change (pNp) is now standard • Then the Internet arrived: • No project can take more than 3 months. • Time to market is everything • Change is good.

  17. 1990 Phones delivered 99.999% ATMs delivered 99.99% Failures were front-page news. Few hackers Outages last an “hour” 2005 Cell phones deliver 90% Web sites deliver 99% Failures are business-page news Many hackers. Outages last a “day” The Internet Changed Expectations This is progress?

  18. AtomicityConsistencyIsolationDurabilty Availability? Strong consistencyIsolation Focus on commit Conservative (Pessimistic) Difficult evolution (e.g. schema) Nested transactions BasicAvailabilitySoft StateEventual Consistency Availability FIRST Weak consistencystale data is OKApproximate answers OK Best effort Aggressive (optimistic) Easier Evolution. Simpler! Faster Eric Brewer said it best:ACID vs BASEthe internet litmus test“copy” of slide 8 of I think it is a spectrum

  19. Why (1) Complexity • Internet sites are MUCH more complex. • NAP • Firewall/proxy/IPsprayer • Web • DMZ • App server • DB server • Links to other sites • tcp/http/html/dhtml/dom/xml/ com/corba/cgi/sql/fs/os… • Skill level is much reduced

  20. A Data Center (500 servers)

  21. A Schematic of HotMail Member MSERVS Front MSERVS Directory • ~7,000 servers • 100 backend stores with 300TB (cooked) • many data centers • Links to • Internet Mail gateways • Ad-rotator • Passport • … • ~ 5 B messages per day • 350M mailboxes, 250M active • ~1M new per day. • New software every 3 months(small changes weekly). Doors Local Director MSERVS Local Director MSERVS Graphics MSERVS Servers Local Director Data MSERVS Data Swittched Ethernet MSERVS Internet AD Servers Data Data Local Director USTORES Incoming MSERVS MSERVS MailServer s Local Director Telnet Management MSERVS Login MSERVS gateway gateway Servers gateway Local Director gateway gateway

  22. Functionality trend Schedule Quality Why (2) Velocity • No project can take more than 13 weeks. • Time to market is everything • Functionality is everything • Faster, cheaper, …

  23. Why (3) Hackers • Hacker’s are a new increased threat • Any site can be attacked from anywhere • Motives include ego, malice, and greed. • Complexity makes it hard to protect sites. • Whole internet attacks: Slammer • Concentration of wealth makes attractive target: Reporter: “Why did you rob banks?” Willie Sutton: “Cause that’s where the money is!” Note: Eric Raymond’s How to Become a Hacker is the positive use of “Hacker”, here I mean malicious and anti-social hackers. Black-hats, not white-hats.

  24. How Bad Is It? Connectivity is poor.

  25. How Bad Is It? • Median monthly % ping packet loss for 2/ 99

  26. And in 2006, about the same

  27. Or In the US

  28. Keynote measures Response Timeand Up Time Measures response time around the world Business service is better than popular service Has many proprietary services for SLAs.

  29. 2006: typical 97.48% Availability 97.48%

  30. Netcraft’s Crisis-of-the-Day

  31. Service Level Measurements • Many organizations are measured on SLAs • Example: 1 sec response 99% of prime time • Keynote, Netcraft, … • offer to monitor you site (probe every few min) • This probing can go deep into the tree to detect services. • Send alerts via email • Give monthly reports.

  32. In addition • Most large sites build their own instrumentation (several times ) • This instrumentation is elaborate and essential for the Network Operations Center (NOC). • There are attempts now to systematize itTivoli, OpenView, NetIQ, WhatsUP, Mom,..

  33. Microsoft.Com • Operations mis-configured a router • Took a day to diagnose and repair. • DOS attacks cost a fraction of a day. • Regular security patches.

  34. Year 1 Through 18 Months Down 30 hours in July (hardware stop, auto restart failed, operations failure) Down 26 hours in September (Backplane failure, I/O Bus failure) Back-End Servers are More Stable • Generally deliver 99.99% • TerraServer for example single back-end failed after 2.5 y. • Went to 4-nodecluster • Fails every 2 mo.Transparent failover in 30 sec.Online software upgradesSo… 99.999% in backend…

  35. eBay: A very honest site • Publishes operations log. • Has 99% of scheduled uptime • Schedules about 2 hours/week down. • Has had some operations outages • Has had some DOS problems.

  36. And 2006…. Welcome to eBay's System Board. Visit this board for information on scheduled site maintenance or system issues that are affecting Marketplace trading. For general eBay news, please see our General Announcements Board. ***Resolved - PayPal site slowness*** February 08, 2006 | 05:20PM PST/PTFor several hours today, members may have experienced slowness while trying to access the PayPal website. This issue has now been resolved. AThank you for your patience. Link to this announcement | Back to top ***PayPal site slowness*** February 08, 2006 | 02:38PM PST/PTMembers may be experiencing intermittent slowness while trying to access the PayPal website. We're aware of this issue and are working to fix it as quickly as possible. Thank you for your patience. Link to this announcement | Back to top ***Scheduled Maintenance For This Week*** February 08, 2006 | 02:03PM PST/PTThe eBay system will be undergoing general maintenance from approximately 23:00 PT on Thursday, February 9th to 01:00 PT on Friday, February 10th. During this maintenance period, certain eBay site features may be intermittently unavailable or slow.

  37. Some Cool New Things • There are 100,000 node services. • Google File System shows importance & benefit of Triplex • DB replication & mirroring works (is easy) • little things I have done • With Leslie Lamport: unified Paxos & 2PC • Measured mean-time-to-data-loss(and continue to measure things).

  38. Outline • The glorious past (Availability Progress) • The dark ages (current scene) • Some recommendations

  39. Not to throw stones but… • Everyone has a serious problem. • The BEST people publish their stats. • The others HIDE their stats (check Netcraft to see who I mean). • We have good NODE-level availability 5-9s is reasonable. • We have TERRIBLE system-level availability 2-9s “scheduled” is the goal (!).

  40. People WANT features! People WANT convenience! People WANT cheap! In exchange,they seem to be willing to tolerate some Un-availability (= inconvenience) “Dirty data” that needs reconciliation Insecurity I see it as our task to make it easier & cheaperto get high availability and Security. Functionality trend Schedule Quality Gresham’s Law:“bad money drives out good”

  41. Recommendation #1 • Continue progress on back-ends. • Make management easier (AUTOMATE IT!!!) • Measure • Compare best practices • Continue to look for better algoritims. • Live in fear • We are at 10,000 node servers • We are headed for 1,000,000 node servers

  42. Recommendation #2 • Current security approach is unworkable: • Anonymous clients • Firewall is clueless • Incredible complexity • We cant win this game! • So change the rules (redefine the problem): • No anonymity • Unified authentication/authorization model • Single-function devices (with simple interfaces) • Only one-kind of interface (uddi/wsdl/soap/…).

  43. Recommendation #3 • Dependability requires holistic not reductionist approach. • It’s the WHOLE system (end-to-end, top-to-bottom) • Hard to publish in this area, hard to get tenure. • Journals want theorem+proof and crisp statements. • Companies want to make money, so do not share their knowledge. • Dependability is an important social good, • So, it Dependability Research needs government or philanthropic sponsorship

  44. References Adams, E. (1984). “Optimizing Preventative Service of Software Products.” IBM Journal of Research and Development. 28(1): 2-14.0 Anderson, T. and B. Randell. (1979). Computing Systems Reliability. Garcia-Molina, H. and C. A. Polyzois. (1990). Issues in Disaster Recovery. 35th IEEE Compcon 90. 573-577. Gray, J. (1986). Why Do Computers Stop and What Can We Do About It. 5th Symposium on Reliability in Distributed Software and Database Systems. 3-12. Gray, J. (1990). “A Census of Tandem System Availability between 1985 and 1990.” IEEE Transactions on Reliability. 39(4): 409-418. Gray, J. N., Reuter, A. (1993). Transaction Processing Concepts and Techniques. San Mateo, Morgan Kaufmann. Lampson, B. W. (1981). Atomic Transactions. Distributed Systems -- Architecture and Implementation: An Advanced Course. ACM, Springer-Verlag. Laprie, J. C. (1985). Dependable Computing and Fault Tolerance: Concepts and Terminology. 15’th FTCS. 2-11. Long, D.D., J. L. Carroll, and C.J. Park (1991). A study of the reliability of Internet sites. Proc 10’th Symposium on Reliable Distributed Systems, pp. 177-186, Pisa, September 1991. Theory and Practice of Reliable System Design, Dan Siewiorek, Robert Swarz Building Secure and Reliable Network Applications, Ken P. Birman Darrell Long, Andrew Muir and Richard Golding, ``A Longitudinal Study of Internet Host Reliability,'' Proc of the Symposium on Reliable Distributed Systems, Bad Neuenahr, Germany: IEEE, 1995, p. 2-9 They have even better for-fee data as well, but for-free is really excellent. eBay is an Excellent benchmark of best Internet practices Empirical Measurements of Disk Failure Rates and Error Rates + C .van Ingen moving 2P with cheap iron “Consensus on Transaction Commit”, +, L. Lamport, unifies 2PC and Byzantie-Paxos