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Charging Models for Data Centers

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Charging Models for Data Centers Bhuvan Urgaonkar The Penn State University Data Centers Clusters of compute and storage servers connected by high-speed nets ... – PowerPoint PPT presentation

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Title: Charging Models for Data Centers


1
Charging Models for Data Centers
  • Bhuvan Urgaonkar
  • The Penn State University

2
Data Centers
  • Clusters of compute and storage servers connected
    by high-speed nets
  • Resources made available to applications
  • Charge the applications for these resources
  • Applications might have clients that they charge

3
Charging in a Data Center
  • Between data center application provider
  • Lease out fixed servers (over-provision)
  • Fixed monthly rate (e.g., yahoo Web hosting)
  • Performance-based charging (mostly research
    prototypes)
  • Usage-based (e.g., Sun Grid)
  • Between application provider clients
  • Fixed monthly rate (possibly with multiple
    classes)
  • Transaction granularity (roughly same as
    usage-based)

4
Classification of Charging Models
  • Flat-rate
  • Usage-based
  • Flat-rate Usage-based
  • Performance-based
  • Bidding-based

5
Flat-rate Charging
  • Local phone service, cable connection
  • () Billing can not get easier
  • (-) Consumer Why should I pay even when I was on
    vacation?
  • (-) Provider Could I have improved my revenue by
    charging based on usage?

6
Usage-based Charging
  • Electricity
  • Actually rate fluctuates!
  • Service interrupted deliberately sometimes
  • Long-distance phone
  • Sun Grid 1/CPU-hour
  • There should be a way for the consumer to verify
    its usage
  • E.g., Electricity meters at our homes

7
Flat-rate Usage-based
  • Cell phones
  • 400 day-time minutes for free
  • Usage-based beyond that

8
Performance-based Charging
  • Service providers like ATT, Sprint guarantee
    average delays in the backbone
  • For data centers
  • Difficult for the data center to translate given
    performance into resources
  • Workloads vary, applications are complex
  • Desirable by application provider
  • Caveat How do I know what response time my
    clients are experiencing?

9
Bidding-based Charging
  • eBay
  • Clients bid till a pre-decided time
  • Highest bidder gets to buy
  • Winning bidder can not back down
  • Open-bid You see what others are doing
  • Closed-bid You dont see what others are doing

10
Bidding-based Charging
  • () Provider This seems to maximize revenue
  • (-) Provider Has to provide bidding mechanism
  • Scalability may be a problem
  • (-) Consumer I have no guarantees some rich guy
    can always shoot me down!
  • (-) Consumer Outcome known only at the end of
    the bid
  • Have to wait till then to make any decisions

11
Possible Factors Governing the Choice of Charging
Model
  • Ease of monitoring and accounting
  • Abundance of resource
  • Competition for the resource
  • Ease of verifying/proving resource usage
  • Dependencies between various resources being
    bought (bidding)
  • Different levels of desirability of the resource
    among the consumers

12
Interlude Differentiated Service
  • When does it make sense to have multiple classes?
  • What decides the priority scheme/scheduling
    discipline?

13
Two Aspects of the Charging Problem
  • Charging Model
  • Economics Problem
  • Accounting and Verification Mechanism
  • Systems Problem

14
Two Aspects of the Charging Problem
  • Charging Model
  • Economics Problem
  • Accounting and Verification Mechanism
  • Systems Problem

15
Charging in a Data Center
  • Which model is suitable?
  • Apps are interested in performance metrics
  • Data center would prefer usage-based charging
  • What about bidding for resources?
  • What does the choice of model depend on?
  • Abundance, competition, peace of mind?
  • Got to be revenue maximization, right?
  • How to charge for the usage of multiple
    resources?
  • CPU, disk, network,

16
Two Aspects of the Charging Problem
  • Charging Model
  • Economics Problem
  • Accounting and Verification Mechanism
  • Systems Problem

17
Two Aspects of theCharging Problem
  • Charging Model
  • Economics Problem
  • Accounting and Verification Mechanism
  • Systems Problem

18
Two Systems Requirements for Enabling Charging
  • Accounting
  • Resource provider should be able to monitor and
    account resource usage
  • Verification
  • Resource consumer should be able to verify its
    own resource usage
  • Ability to dispute providers claims

19
Accounting
  • Well studied by OS and networks communities
  • Resource containers from Rice University
  • Mostly an engineering exercise
  • Does the problem become any harder in a
    virtualized hosting environment?

20
Verification
  • Remember App doesnt trust the data center
  • Auditing Instead of verifying resource usage at
    all times, the consumer does it sometimes
  • The provider should not be able to predict or
    detect an audit
  • Audit at random
  • Provider and consumer should agree to the
    auditing process
  • Involve a third party that both trust
  • The data center also doesnt trust the
    application!
  • Failing an audit is a violation of SLA

21
Auditing in a Data CenterExhaustive Profiling
  • The auditor uses extensive profiling to identify
    resource usage to performance mapping for all
    possible workloads
  • () The data center can not figure out it is
    being audited
  • (-) Such profiling might be prohibitively
    expensive

22
Auditing in a Data CenterSelective Profiling
  • The auditor sends well-profiled probes and
    observes their performance
  • () No need for extensive/exhaustive profiling
  • (-) Data center might identify probes
  • Camouflage needed
  • (-) Not trivial to construct probes whose
    performance is independent of the rest of the
    workload

23
Auditing in a Data CenterSelf-Monitoring
Applications
  • Assume it is possible to modify the application
  • Can the application monitor its own resource
    usage?
  • Can not trust the underlying OS/VMM

24
Self-Monitoring Application
  • Idea We add a special auditing code (AC) to the
    application
  • for (i0 i lt 1000000 i)
  • At a randomly chose time t1, the application
    sends a message to the auditor
  • The application jumps to AC and starts executing
    it
  • The auditor ACKs the message
  • The application receives the ACK at time t2 and
    determines t2-t1, compares it with expected time
    to reach the current value of i

25
Problems with Self-Monitoring Applications
  • The execution time of AC depends on what other
    apps are doing
  • Not a problem data center expected to guarantee
    lower bounds
  • Unpredictable delays in the Internet
  • Send multiple probes and take average
  • The auditor could record probe reception times
    and try to adjust for network delays

26
Problems with Self-Monitoring Applications
  • How to ensure data center can not identify a msg
    to auditor or the execution of AC?
  • Msg to auditor and ACK should look like normal
    requests and responses
  • Giveaway Data center observes that the
    application has become CPU-intensive suddenly
  • Not a problem if the app becomes CPU-intensive
    when serving its normal workload
  • Need to ensure that the CPU usage during the
    execution of AC is indistinguishable from that
    when serving normal workload
  • E.g., Running a while loop that lasts 30 min
    would be a bad idea

27
Design Issues Self-Monitoring Applications
  • What is the right observation period? How many
    observations should be made?
  • What about other resources?
  • Network bandwidth perhaps similar to CPU
  • Memory and disk bandwidth much harder!

28
Summary
  • Charging in data centers seems like an important
    problem to address
  • We can break-down the charging problem into
  • Charging model Economics problem
  • Accounting and verification Systems problems
  • Many interesting open issues!
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