The document provides an overview of the SLALOM project, which aims to develop a core service level agreement (SLA) specification that can serve as a basis for interactions between cloud service providers and customers. It discusses SLALOM's contributions, including an SLA specification model that extends existing standards and an abstract definition of metrics that clarifies measurement ambiguities. An example is provided mapping the Amazon EC2 SLA to the SLALOM framework to demonstrate how it handles definitions at the sample, period, and metric levels.

1. SLALOM Webinar
George Kousiouris, Andreas Menychtas,
Dimosthenis Kyriazis
ICCS/NTUA

2. Outline
• SLALOM Project
• Our background
• Overview of contributions
• SLA specification / reference model
• Abstract metric function / definition
• Conclusions
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3. SLALOM Project
• EU funded project started on January 2015
• Aims at developing a core SLA specification
– As a basis for service interactions between providers and customers
– Considering current SLA landscape and research outcomes from
various projects and initiatives
• Current status
– Analysis of SLA landscape, standardization efforts, relevant research
outcomes
– Development of SLA specification (v1) including main blocks and
components for each component
– Development of abstract metric / function (v1) applicable to different
metrics
– Submission of our work to ISO SLA WG for standardization
• SLALOM is officially accepted as liaison body to ISO SLA WG
• Attended and presented our work in the last ISO SLA WG meeting (Dublin)
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4. Our Background
• European Commission Expert Group on SLAs,
http://ec.europa.eu/digital-agenda/en/news/cloud-computing-
service-level-agreements-exploitation-research-results
• Real time SLAs (IRMOS FP7 project, 2008-2011)
– Real Time Cloud for enabling performance guarantees on soft real-
time applications via SLAs
• Admission Control and Legal Aspects (OPTIMIS FP7 project, 2010-
2013)
– Risk, Eco-efficiency and Cost as parameters
– Data Location considerations, Contractual terms
• Abstracted Auditing/Monitoring of SLAs (ARTIST FP7 project, 2012-
2015)
– 3ALib abstracted library implementation
– CloudML@ARTIST definition of a UML profile for SLA descriptions
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5. Outline
• SLALOM Project
• Our background
• Overview of contributions
• SLA specification / reference model
• Abstract metric function / definition
• Conclusions
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6. SLA Specification Contribution (1/2)
• The proposed specification / reference model takes into
account
– Standardization approaches and working groups outcomes
– Current SLAs offered by commercial cloud providers
– Expressed views by cloud providers and adopters
– Research outcomes
• With respect to ISO SLA WG outcomes
– Follows ISO 19086-2: Core blocks (i.e. metric definition,
parameters definition, rule definition) and the corresponding
elements (e.g. ID, name, unit, scale, etc) of the SLA
– Follows ISO 3534-2: Metric in different scales (such as interval,
ratio, nominal or ordinal)
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7. SLA Specification Contribution (2/2)
• With respect to ISO WG outcomes (cont.)
– Suggests changes to ISO 19086-2: Naming of specific
elements (e.g. referenceId is used both for metricId
for parameterId and for ruleId, while SLALOM
proposes the use of different identifiers)
– Suggests changes to ISO 19086-2: Inclusion of
additional elements and blocks:
• Dependencies with other metrics - e.g. availability of storage
service and dependency to latency or response time and
dependency to bandwidth
• Importance of a metric (i.e. gradeOfImportance)
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8. SLA Specification / Reference model:
Main blocks
• Follows ISO 19086-2 SLA specification
• Metric
– Corresponds to the service metric / objective (e.g. availability)
• Parameter
– Links the metric with a parameter to express how it can be
monitored and validated (e.g. time to provide resources
following an elasticity trigger)
• Rule
– Refers to metric “constraints” (e.g. number of concurrent
connections for a number of users metric)
• SLALOM proposed the addition of the Dependency block
– Captures dependencies between metrics (e.g. response time
and bandwidth)
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9. Components
• Specific components are used for all building blocks
– ID
– Name
– Definition / Expression
– Unit
– Notes
• SLALOM proposed the following additions to the ISO
specification
– gradeOfImportance component for the Metric definition, to
define the metrics importance within an SLA
– consequenceOfViolation component for the Rule definition, to
define the potential consequence of violation on the service
provisioning
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10. Outline
• SLALOM Project
• Our background
• Overview of contributions
• SLA specification / reference model
• Abstract metric function / definition
• Conclusions
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11. Abstract metric function / definition primary goal
• Have a standard that forces ambiguities to be clarified
• Help in the measurement/auditing process of an SLA
– Especially by 3rd party providers
– What is the purpose of having SLAs if one is not able to measure them
non-repudiably?
• Abstract the process
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12. Example of ambiguity in the measurement process: AWS EC2 SLA
• ““Unavailable” and “Unavailability” mean:
– For Amazon EC2, when all of your running instances have no
external connectivity.”
• Determination of external connectivity. How?
– E.g. pinging (ICMP)?
• Security threat
– Application layer (endpoint checking)?
• Includes application downtime (Not the responsibility of AWS EC2)
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13. SLALOM 3-Layer Definition
Metric (Ratio) Layer
Final ratio calculation of the defined metric Correlates individual periods to the overall metric
Period (Time) Layer
Size of period, limit of base period and on the error
rate needed
Aggregates samples at a time interval granularity,
deciding on this level
Sample (Measurement) layer
Boolean expression based on concrete measurement
constraints
Dictates success or not of a sample
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14. Sample Layer
• Sample Condition - sc: the condition stating whether a sample has been successful.
– operator: the operator can either be a boolean one (i.e. AND, OR, NOT) or a comparison
operator (<, >, <=, >=, ==, !=).
– value: the actual value of the condition that can be arithmetic, non-arithmetic (e.g. a
string such as “exception”) or an enumeration (e.g. HTTP response code == 200).
– unit: the unit for the value of the condition.
• Sample - s: the sample used to evaluate a parameter against the condition sc.
• Successful Sample - ss: the sample satisfying the condition sc.
• Unsuccessful Sample - us: the sample not satisfying the condition sc.
• Type of Operation field: defined sampling process e.g. pair of protocol- response
Sample definition
For a given type of operation as specified in the corresponding field (described
previously)
sc = operator + value + unit
ss = s if (sc is true)
us = s if (sc is false)
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15. Period Layer
• Boundary Period - bp: the period for which the analysis of a parameter (through samples) should be
taken into account. Any sample that is not meeting this criterion (i.e. falls within the period) is
excluded even though if it is successful (i.e. ss according to the sample definition).
– operator: a comparison operator (<, >, <=, >=, ==, !=).
– value: the actual arithmetic value of the condition.
– unit: the unit in this case is always a time unit (e.g. seconds, minutes, etc).
• Error Condition - ec: the error condition ratio for which the analysis of a parameter (through samples)
should be taken into account. The ratio is always expressed in a percentage (%) format.
– operator: a comparison operator (<, >, <=, >=, ==, !=).
– value: the actual arithmetic value of the condition.
• Error Ratio - er: the error ratio calculated based on the total set of samples and the successful
samples.
• Period - p: the period in which samples (sc and uc) are examined according to the boundary period
and the error condition.
• Valid Period - vp: the period for which the error ratio value meets the error condition ratio and the
boundary period condition is also satisfied.
• Non-valid Period - np: the period for which the error ratio value does not meet the error condition
ratio (the boundary period condition is satisfied). Boundary period and error definitions
bp = operator + value + unit
ec = operator + value + %
er = Σus/Σs ∀us ∈ p
vp = p if ((er<=ec) && (p>=bp))
np = p if ((er>=ec) && (p>=bp))
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16. Metric Layer
• Metric Condition - mc: the condition regarding a specific metric. The
condition is always expressed in a percentage (Ratio Type?) (%) format to
enable its evaluation as proposed through the metric evaluation.
– operator: a comparison operator (<, >, <=, >=, ==, !=).
– value: the actual arithmetic value of the condition.
• Metric Evaluation - me: the evaluation of the metric based on the valid
and non-valid period samples. The evaluation should be smaller than the
condition (i.e. me <mc).
Abstract metric definition
mc = operator + value + %
me = Σnp / (Σvp+Σnp)
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17. Mapping of EC2 SLA@SLALOM
Amazon EC2
Level / definition Expression Notes
Sample definition sc: UNDEFINED (assumed ‘ping’->
ICMP)
The sampling condition is not defined in the
Amazon EC2 SLA. The concrete wording is “when
all of your running instances have no external
connectivity”. Nonetheless, the way to specify /
measure “external connectivity” is not defined.
For example a customer could use a ping
operation or a custom monitoring mechanism.
Type of operation: ping Not defined how the condition of connectivity
can be actually measured (e.g. the ping
operation mentioned previously).
Boundary period
and error
definitions
bp > 60 sec The exact wording is “the percentage of
minutes”, thus the period is 60 seconds.
ec = 100% Error condition reflecting that the error ratio is
that for the entire bp the resource must be
continuously “unavailable”.
Abstract metric
definition
availability < 99.95 % Availability metric definition given the boundary
period and error condition.
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18. Mapping of SLALOM @ GAE Datastore
Google AppEngine Datastore
Level / definition Expression Notes
Sample definition sc: INTERNAL_ERROR Several sampling conditions are
defined per type of operation. For
example it is specified (exact wording)
“INTERNAL_ERROR, TIMEOUT, …” for
API calls.
Type of operation: API calls Several type of operations are defined.
An example is provided here.
Boundary period
and error
definitions
bp > 300 sec The exact wording is “five consecutive
minutes”.
ec > 10% Error condition reflecting that the
error ratio is (exact wording) “ten
percent Error Rate”.
Abstract metric
definition
availability < 99.95 % Availability metric definition given the
boundary period and error condition.
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19. Mapping of SLALOM @ Microsoft
Azure SLA
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Microsoft Azure Storage
Level / definition Expression Notes
Sample definition sc = 60 sec Several sampling conditions are defined
per type of operation. For example it is
specified (exact wording) “Sixty (60)
seconds” for PutBlockList and
GetBlockList.
Type of operation: PutBlockList and
GetBlockList
Several type of operations are defined.
An example is provided here.
Boundary period
and error
definitions
bp > 3600 sec The exact wording is “given one-hour
interval”.
ec > 0% Error condition reflecting that all periods
should be taken into account for the
availability metric evaluation (exact
wording) “is the sum of Error Rates for
each hour”.
Abstract metric
definition
availability < 99.9 % Availability metric definition given the
boundary period and error condition.

20. Preconditions
• For any SLA to apply, a number of preconditions
typically exist per provider
• Examples
– Deployment: Number of Availability Zones used
– Deployment: Replication options used
– Usage/Measurement: Restarting of resources when
unavailable
– Usage/Measurement: Applied Throttling of requests
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21. Outline
• SLALOM Project
• Our background
• Overview of contributions
• SLA specification / reference model
• Abstract metric function / definition
• Conclusions
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22. Snapshot of SLA contributions
• An SLA specification / reference model (captured in
SLALOM SLA Specification and Reference Model v1:
http://slalom-project.eu/content/d32-%E2%80%93-sla-
specification-and-reference-model)
– Follows and proposes changes to ISO 19086-2
– Follows ISO 3534-2
• An abstract metric function / definition that can be
exploited to specify any SLA metric (captured in
SLALOM SLA Metric Specification v1: http://slalom-
project.eu/content/slalom-sla-specification-v1-sep-
2015)
– Submitted as contribution to ISO 19086-2
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23. Feedback
• Please provide us feedback on the presented
concepts at:
• https://docs.google.com/forms/d/1Ljnc2x2WS
aAXrWzHglDyy31xdCNC3qDiQqhC1FoxDZI/vie
wform
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24. Any questions?
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www.slalom-project.eu

25. 3ALib (Availability SLA Benchmark and Auditor)
• Abstracted Availability Auditor Library (Java-based) Implementation:
– Based on the conceptual abstractions of different providers SLAs
– Abstracted at the code level, for efficient replacement of processes
and inclusion of providers
• Purpose:
– Align monitoring with specific provider definitions and adapt
availability calculations
– Check preconditions of SLA applicability for a specific deployment and
give feedback
– Adapt to dynamic Cloud Services user behavior
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26. Details for GAE Datastore SLA
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27. Details for Azure SLA
Transaction Type Maximum Processing Time*
 PutBlob and GetBlob (includes blocks
and pages)
 Get Valid Page Blob Ranges
Two (2) seconds multiplied by the number of MBs
transferred in the course of processing the
request
 Copy Blob Ninety (90) seconds (where the source and
destination blobs are within the same storage
account)
 PutBlockList
 GetBlockList
Sixty (60) seconds
 Table Query
 List Operations
Ten (10) seconds (to complete processing or
return a continuation)
 Batch Table Operations Thirty (30) seconds
 All Single Entity Table Operations
 All other Blob and Message Operations
Two (2) seconds
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