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

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dependability in the internet era

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

outline
Outline
  • The glorious past (Availability Progress)
  • The dark ages (current scene)
  • Some recommendations
preview the last 10 years availability dark ages ready for a renaissance

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

dependability the 3 ities
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

fail fast is good repair is needed
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.

fault model
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
disks raid the big success story
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.
fault tolerance vs disaster tolerance
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.
availability

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

case study japan survey on computer security japan info dev corp march 1986 trans eiichi watanabe
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

case studies tandem trends
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

dependability status circa 1995
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.
honorable mention
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.
and then
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.
outline15
Outline
  • The glorious past (Availability Progress)
  • The dark ages (current scene)
  • Some recommendations
progress

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.
the internet changed expectations
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?

slide18
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 http://www.ccs.neu.edu/groups/IEEE/ind-acad/brewer/sld008.htm

I think it is a spectrum

why 1 complexity
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
a schematic of hotmail
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

why 2 velocity

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, …
why 3 hackers
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 Hackerhttp://www.tuxedo.org/~esr/faqs/hacker-howto.html

is the positive use of “Hacker”, here I mean malicious and anti-social hackers.

Black-hats, not white-hats.

how bad is it
How Bad Is It?

http://www-iepm.slac.stanford.edu/

Connectivity is poor.

http://www.internettrafficreport.com/main.htm

how bad is it25
How Bad Is It?

http://www-iepm.slac.stanford.edu/pinger/

  • Median monthly % ping packet loss for 2/ 99
keynote measures response time and up time
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.

service level measurements
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.
in addition
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,..
microsoft com
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.
back end servers are more stable

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…
ebay a very honest site
eBay: A very honest site

http://www2.ebay.com/aw/announce.shtml

  • Publishes operations log.
  • Has 99% of scheduled uptime
  • Schedules about 2 hours/week down.
  • Has had some operations outages
  • Has had some DOS problems.
and 2006
And 2006….

http://www2.ebay.com/aw/announce.shtml

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.

some cool new things
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).
outline39
Outline
  • The glorious past (Availability Progress)
  • The dark ages (current scene)
  • Some recommendations
not to throw stones but
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 (!).
gresham s law bad money drives out good
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”
recommendation 1
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
recommendation 2
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/…).
recommendation 3
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
references
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

http://www.netcraft.com/ They have even better for-fee data as well, but for-free is really excellent.

http://www2.ebay.com/aw/announce.shtml#top 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   

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