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TAPAS @ UCL. Wolfgang Emmerich. People. Cecilia Mascolo (from April 2002) Wolfgang Emmerich (from April 2002) Nima Kaveh @ 50% (from April 2002) Davide Lamanna @ 50% (from Sept 2002) A. N. Other (Interviews on 12/04/2002). Research to TAPAS @ UCL. EPSRC Promile (Programmable Networks) - PowerPoint PPT Presentation
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1© Wolfgang Emmerich, 2002
TAPAS @ UCLTAPAS @ UCL
Wolfgang EmmerichWolfgang Emmerich
2© Wolfgang Emmerich, 2002
PeoplePeople
Cecilia Mascolo (from April 2002) Wolfgang Emmerich (from April 2002) Nima Kaveh @ 50% (from April 2002) Davide Lamanna @ 50% (from Sept 2002) A. N. Other (Interviews on 12/04/2002)
Cecilia Mascolo (from April 2002) Wolfgang Emmerich (from April 2002) Nima Kaveh @ 50% (from April 2002) Davide Lamanna @ 50% (from Sept 2002) A. N. Other (Interviews on 12/04/2002)
3© Wolfgang Emmerich, 2002
Research to TAPAS @ UCLResearch to TAPAS @ UCL
EPSRC Promile (Programmable Networks) Kodak MANIAC (QoS aware Image
Processing Services) BT Studentship on Middleware for
Programmable Networks Studentship Qualitative Analysis of
Distributed Object Design
EPSRC Promile (Programmable Networks) Kodak MANIAC (QoS aware Image
Processing Services) BT Studentship on Middleware for
Programmable Networks Studentship Qualitative Analysis of
Distributed Object Design
4© Wolfgang Emmerich, 2002
Service Level AgreementsService Level Agreements
Wolfgang Emmerich and Davide Lamanna
Dept. of Computer Science
University College London
{w.emmerich|d.lammana}@cs.ucl.ac.uk
Wolfgang Emmerich and Davide Lamanna
Dept. of Computer Science
University College London
{w.emmerich|d.lammana}@cs.ucl.ac.uk
5© Wolfgang Emmerich, 2002
AgendaAgenda
Service Level Agreements (SLAs) Service Level Specifications (SLSs) Horizontal vs. Vertical SLSs SLS Monitoring SLS Enforcement Research Questions
Service Level Agreements (SLAs) Service Level Specifications (SLSs) Horizontal vs. Vertical SLSs SLS Monitoring SLS Enforcement Research Questions
6© Wolfgang Emmerich, 2002
Service Level Agreements (SLAs)Service Level Agreements (SLAs)
SLA are a means for customers to express their service level needs and for ASPs to distinguish their services
Typically appendixes to legal contracts ASPs are still struggling to define SLA and
manage the service levels Typical SLA of ISPs include availability, latency,
and time for error notification Also important are problem resolution speed
and resources Refunds are made only upon customer claim in
many cases
SLA are a means for customers to express their service level needs and for ASPs to distinguish their services
Typically appendixes to legal contracts ASPs are still struggling to define SLA and
manage the service levels Typical SLA of ISPs include availability, latency,
and time for error notification Also important are problem resolution speed
and resources Refunds are made only upon customer claim in
many cases
7© Wolfgang Emmerich, 2002
ExampleExample
MarketplaceVendor1
Vendorn
Buyer
Credit Rating Agency
Retail Bank1 Retail Bankn
ASP
ISP SSP
TTP
8© Wolfgang Emmerich, 2002
Typical SLA ContentTypical SLA Content
Parties of the agreement Purpose of the SLA Duration of agreement Description of service:
• Service overview• Corporate dependence• Priority• Critical/peak periods• Service level components
– Availability– Transactions – Response– Utilization – Accuracy and – Security
Parties of the agreement Purpose of the SLA Duration of agreement Description of service:
• Service overview• Corporate dependence• Priority• Critical/peak periods• Service level components
– Availability– Transactions – Response– Utilization – Accuracy and – Security
Targets and metrics for measurement
Scheduled unavailability for maintenance/changes
Support hours Charging agreements Monitoring actual service
levels against targets Responsibilities Service level reporting Penalties for failure Customer service review
meetings/renegotiations Contacts
Targets and metrics for measurement
Scheduled unavailability for maintenance/changes
Support hours Charging agreements Monitoring actual service
levels against targets Responsibilities Service level reporting Penalties for failure Customer service review
meetings/renegotiations Contacts
9© Wolfgang Emmerich, 2002
Design by Contract (Meyer 1988)Design by Contract (Meyer 1988)
Component models provide primitives to design service functionality in interfaces (contracts)
How do we specify non-functional aspects (service levels) of contracts between independent parties?
Service Level Specifications (SLS) are SLAs formalized for automated enforcement and monitoring
Component models provide primitives to design service functionality in interfaces (contracts)
How do we specify non-functional aspects (service levels) of contracts between independent parties?
Service Level Specifications (SLS) are SLAs formalized for automated enforcement and monitoring
10© Wolfgang Emmerich, 2002
Horizontal vs. Vertical SLSsHorizontal vs. Vertical SLSs
Assume use of components for assembly of distributed application services
We require horizontal SLSs that govern interaction between components
We also need vertical SLSs that govern the support components get from their infrastructure:• Component Containers• Storage Service Providers• Internet Service Providers
Assume use of components for assembly of distributed application services
We require horizontal SLSs that govern interaction between components
We also need vertical SLSs that govern the support components get from their infrastructure:• Component Containers• Storage Service Providers• Internet Service Providers
11© Wolfgang Emmerich, 2002
Horizontal SLSsHorizontal SLSs
Specified using component meta model E.g. A market place component
guarantees to a buyer component for a rate below 10 remote method invocations per second a response time of 0.5 milliseconds
Specified using component meta model E.g. A market place component
guarantees to a buyer component for a rate below 10 remote method invocations per second a response time of 0.5 milliseconds
Marketplace
Vendor1
VendornBuyer
Credit Rating Agency
12© Wolfgang Emmerich, 2002
Vertical SLSsVertical SLSs
Specified referring to infrastructure interfaces
E.g. • Replication levels• Network latency• Storage
Specified referring to infrastructure interfaces
E.g. • Replication levels• Network latency• Storage
Marketplace
ASP
ISP SSP
13© Wolfgang Emmerich, 2002
SLS MonitoringSLS Monitoring
How well do components / infrastructure abide by the service levels determined in an SLS?
Measure metrics defined in the SLS, e.g. times required to execute certain operations
Component infrastructure needs to interpret SLS and generate alerts to administrators if metrics indicate that service levels have been violated
How well do components / infrastructure abide by the service levels determined in an SLS?
Measure metrics defined in the SLS, e.g. times required to execute certain operations
Component infrastructure needs to interpret SLS and generate alerts to administrators if metrics indicate that service levels have been violated
14© Wolfgang Emmerich, 2002
SLS EnforcementSLS Enforcement
Rather than reactively alert SLS violations use component infrastructure to enforce service levels, e.g.• Increase response time of remote requests
between components by tightening vertical service level specifications
• Increase scalability of component execution before it is to violate service level specifications by proactively replicating them
Rather than reactively alert SLS violations use component infrastructure to enforce service levels, e.g.• Increase response time of remote requests
between components by tightening vertical service level specifications
• Increase scalability of component execution before it is to violate service level specifications by proactively replicating them
15© Wolfgang Emmerich, 2002
Research Questions for TAPASResearch Questions for TAPAS
Language(s) for service level specification
Seamless integration of functional with non-functional design
Parameterisation of service level specifications
Compositionality of service level specifications
Validation of service level specifications
Language(s) for service level specification
Seamless integration of functional with non-functional design
Parameterisation of service level specifications
Compositionality of service level specifications
Validation of service level specifications
16© Wolfgang Emmerich, 2002
Summary and ConclusionsSummary and Conclusions
Service level agreements are human readable definitions of non functional characteristics
Service level specifications are formal specifications that are monitored and enforced by component infrastructure
Service level specifications impose a number of interesting research questions for TAPAS
Service level agreements are human readable definitions of non functional characteristics
Service level specifications are formal specifications that are monitored and enforced by component infrastructure
Service level specifications impose a number of interesting research questions for TAPAS
