autonomous resource provisioning for multi-service web applications jiang dejun,guillaume...

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AUTONOMOUS RESOURCE PROVISIONING FORMULTI-SERVICE WEB APPLICATIONSJiang Dejun,Guillaume Pierre,Chi-Hung Chi

WWW '10 Proceedings of the 19th international conference on World wide web

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Agenda

Introduction Related Work Autonomous Provisioning Evaluation Conclusion Comments

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Introduction(1/5)

Major web sites such as Amazon.com and eBay Are not designed as monolithic 3-tier

applications but as a complex group of independent services querying each other

A service is a self-contained application providing elementary functionality database holding customer information an application serving search requests

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Introduction(2/5)

To provide acceptable performance to their customers providers often impose themselves a

Service Level Agreement (SLA) apply dynamic resource provisioning to respect

the SLA target by adding resources when violating the SLA

removing resources when possible without violating the SLA

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Introduction(3/5)

An essential question in resource provisioning of multiservice web applications select which service(s) should be

(de-)provisioned such that the whole application maintains acceptable performance at minimal cost.

This is a challenge because multi-service applications involve large number of components that have complex relationships with each other

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Introduction(4/5)

Two possible approaches models the entire application as a single queuing network

Too complex to capture all services relationships assigns a fixed SLA to each service separately

May waste resources Only the front-end service should be given an SLA

each service should be autonomously responsible for its own provisioning by collaboratively negotiating its performance objectives

with other services to maintain the front-end’s response time

“What-if analysis”

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Introduction(5/5)

The authors show the system which can effectively provision resources to both traditional multi-tier web application complex multi-service applications

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Related Work

Resource provisioning for single-tier [1,4] or multi-tier Web applications [7,10,12,14,15,17]

In [18], model work flow patterns within multiservice applications to predict future workloads for each services component

In [15,16], the works focus on when resources should be provisioned But allocating new resources becomes

much faster now

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Autonomous Provisioning – System Model(1/5)

A service a single-tier functional service with an HTTP or

SOAP interface hosted in an application server a single-tier data service with an SQL

interface hosted in a database server Within a multi-service application

Services are commonly organized as a directed acyclic graph

assume that the services of one application are not used simultaneously by other applications

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assume that some machines are always available to be added to an application

Each resource can be assigned to only one service at a time Such resource may be a physical machine

or a virtualized instance with performance isolation

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Predict

Negotiation

Global Decision

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Step 1: each service carries out “what-if analysis” to predict its

future performance If the service was assigned an extra machine or removed one

Periodically send result to parent node Step 2:

Intermediate node selects the maximum performance gain and minimum loss among the children nodes and itself

Finally: Root node select which service(s) to provision when the

SLA is (about to be) violated

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Autonomous Provisioning – Performance Model(1/3)

use an M/M/n/PS queue to capture the performance of an n-core machine

Expected Response Time: Rserver : the average response time of the

service n : the number of CPU cores assigned to

service λ : the average request rate Sserver : the mean service time

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A service may also use caches to offload some of the incoming requests from the service itself.

Adding caches potentially improves response time for two reasons First, cache hits are processed faster than

cache misses. Second, the service itself and all children

nodes receive less requests, and can thus process them faster

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The performance model calculates the caching impact on the response time as follows R(m) : the response time of the backend

server across m CPU cores Scache : the cache service time ρn : the expected cache hit ratio with n

nodes

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Autonomous Provisioning – Model parameterization(1/5)

Most of the model parameters can be measured offline or monitored at runtime. the request rate can be monitored by the

administrative tools of application servers and database servers

The cache service time can be obtained by measuring cache response time offline

But expected cache hit ratio(ρn) and mean service time(Sserver) are harder to measure

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Expected cache hit ratio(ρn) Using virtual caches Stores only metadata such as the list of

object in caches and their sizes It receives all requests directed to the

service and applies the same operations as a real cache with the same configuration would

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Mean service time(Sserver) Previous research works measure the service time via

profiling under low workload But authors found that while workload increases, the

prediction error rate become higher

To achieve acceptable prediction results, authors apply a classical feedback control loop to adjust the service time at runtime. The system continuously estimates the service’s

response time under the current conditions and compares the error between the predicted response time and the measured one.

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Define a threshold as a configuration parameter If the error rate exceeds the threshold,

recomputed the service time S’server : the corrected service time Rserver : the latest measured response time n : the number of current CPU cores λ: the current request rate

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Autonomous Provisioning – Resource Provisioning of service instances (1/3)

Each service reports performance promises to its parent on behalf of its children and itself: it reports the best performance gain (loss)

possible by adding (removing) a server to (from) a service of the subtree consisting of its children nodes and itself.

Assuming a service i has k immediate children services Vi,J : the average number of service executions on

service J caused by one request from service i

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Autonomous Provisioning – Resource Provisioning of cache instances (1/3)

Provisioning cache instances is harder it not only changes the performance of the

concerned service, but also changes the traffic to its children, which in turn affects their performance

Each service periodically informs its children of the relative workload decrease (increase) it would address to them if it was given one more (one less) cache instance

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To calculate expected traffic EIR : expected invocation ratio = expected

cache miss rate Vi,j : the average number of service

executions on service j caused by one request from service i

Wi : the request rate of node i K : the number of predecessors in the

graph

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Autonomous Provisioning – Shifting Resource Among Services

In many cases, it can be more efficient to simply reorganize resource assignments within the application without retrieving machines from the resource pool Vi,j may change due to an update in the

application code or a change in user behavior

Shifting resource may be an oscillating behavior To prevent it, one should define a

performance threshold as the criterion for deciding whether to shift

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Evaluation – Experimental Setup(1/3)

All experiments are performed on the DAS3 cluster at VU University Amsterdam. The cluster consists of 85 nodes

a dual-CPU/dual-core 2.4GHz AMD Operon DP 280 4GB RAM a 250 GB IDE hard drive

Nodes are connected with a 10Gbps LAN the network latency between nodes is negligible

set the prediction error threshold for dynamically adjusting the service time to 3%.

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Author implement the local performance monitor on application server using the MBean servlet from JBoss.

The database server monitoring is based on performance data collected by the admin tool of MySQL.

Author developed the negotiation agent in Java using plain sockets.

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Evaluation – Model Validation(1/2)

Compare predicted values with the measured response times using the “XSLT” and “Product” services

from Figure 7(c) separately Set the SLA of each service to a maximum

response time of 400ms Initially assign one server to each

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Evaluation – Model Validation(2/2)

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Evaluation – Comparison(1/2)

Comparison with “Analytic” Figure 7(a) A well known model Set SLA of 500ms for the whole application Analytic does not address multi-service

application

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Evaluation – Comparison(2/2)

Comparison with per-service SLA Figure 7(b) Set SLA to 500ms

12 req

12 req

16 req

16 req

25 req

23 req

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Evaluation – Provisioning under varying load intensity(1/2)

Using figure 7(c) and 7(d) Set SLA of 500ms Workload first increases from 2 req/s to

22 req/s, then decrease back to 2 req/s

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Evaluation – Provisioning under varying load intensity(2/2)

10 req

18 req

16 req

8 req

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Evaluation – Provisioning under varying load distribution(1/2)

Add workload to Service 2 and 3 at the same rate

At time 35, the workload of service 3 decrease while workload of service 2 increase as the same

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Evaluation – Provisioning under varying load distribution (2/2)

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Evaluation – Provisioning under varying load locality (1/2)

Define locality as the hit rate for a cache holding 10,000 objects

Increase workload until time 25 when the SLA was violated , and then changing the locality of service3

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Evaluation – Provisioning under varying load locality (2/2)

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Conclusion

The paper takes a different stand and demonstrates that provisioning resources for multi-service applications. Which can be achieved in a decentralized way

where each service is autonomously responsible for its own provisioning

Propose to give an SLA only to the front-end service

To author’s best knowledge, no other published resource provisioning algorithm can match or outperform their approach

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Comments

The paper is using physical machines as resources In virtual machine, we can dynamic set

each VM’s CPU upper bound It means that maybe we can make the cost less

than the paper The paper is more complex than what

we want to do now, but there are something we can refer to Something like the approach of adjusting

the profiling

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The End Thanks

autonomous resource provisioning for multi-service web applications jiang dejun,guillaume...

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