Journal of Software Engineering and Applications, 2013, 6, 114-117
doi:10.4236/jsea.2013.63b025 Published Online March 2013 (http://www.scirp.org/journal/jsea)
HA-SLA: A Hierarchical Autonomic SLA Model for SLA
Monitoring in Cloud Computing
Ahmad Mosallanejad, Rodziah Atan
Faculty of Computer Science and Information Technology, Universiti Putra Malaysia, Malaysia.
Received 2013
ABSTRACT
Service Level Agreement (SLA) is a fundamental contract between service consumer and service provider which de-
fined the qualities of agreed service. After SLA contraction, it should be monitored during the service invocations to
confirm the service level objectives. Most of SLA structure and monitoring frameworks are brought from SOA and grid
computing to cloud computing environment while they have different requirements. In this paper, a model is proposed
as hierarchical autonomic (HA)-SLA based on cloud computing nature. It is proposed in this model that each SLA has
connection with dependent SLAs in different layers of cloud computing, hierarchically, whereby each SLA should be
able to monitor its attributes on its own. It is expected that HA-SLA model should able to increase SLA validity and
users’ confidence without compromising the respond time. The results produced by this model should be used as one of
cloud computing quality of service assurance.
Keywords: Service Level Agreement (SLA); Cloud Computing; SLA Monitoring; Self-Management SLA
1. Introduction
Nowadays, interaction for services between consumers
and providers are increasing dramatically within the
cloud computing environment. A service level agreement
(SLA) is a basis of all relations between consumers and
providers. SLA includes service functionalities and qual-
ity of service (QoS) which identifies the service level
objective (SLO). The SLA contents are defined after a
negotiation process between service consumer and pro-
vider. Then, the user expects to use the service based on
SLA features and the provider is responsible about any
violated SLA. Therefore, an effective SLA monitoring
system is essential to inspecting the SLO during the ser-
vice invocations.
The current SLA and monitoring frameworks are not
completely based on cloud computing requirements [1].
Most of them are designed for service oriented architec-
ture (SOA) and grid computing which are having a dif-
ferent nature with cloud environment [2]. Some of these
SLA monitoring systems are being applied in cloud
computing without modification. Cloud computing ar-
chitecture is hierarchical in nature. It includes the layers
of Infrastructure as a service (IaaS), platform as a service
(PaaS) and software as a service (SaaS).
This paper proposes a hierarchical autonomic (HA)-
SLA model for SLA monitoring in cloud computing
which has less attempt by the community. This model
provides a hierarchical SLAs based on hierarchical na-
ture of cloud computing. So, each SLA is connected to
the related SLAs in IaaS, PaaS and SaaS layers for send-
ing an essential notification as a current SLA state.
Moreover, each SLA is autonomic to manage and moni-
tor its features itself which provides a self-management
SLA. The proposed model is simulated and it is validated
by experimental methodology.
In this paper, related works are discussed in Section 2,
and HA-SLA model is described in Section 3. Next, the
proposed model implementation is presented in Section 4.
Finally, the HA-SLA evaluation and conclusion are illus-
trated in Sections 5 and 6 respectively.
2. Related Work
Many studies discussed SLA and SLA monitoring but
less focus has been put in cloud computing area. In some
of these researches, the SLA structure and monitoring
system are brought from SOA and grid computing to
cloud computing environment without enough attention
to cloud computing unique features. This shortcoming is
repeated in RESTful [3], SALmonADA [4] and SLA@
SOI [5] frameworks.
An appropriate set of SLA attributes are described in
[6] for different layers of cloud computing, separately
and specified based on IaaS, PaaS and SaaS requirements;
however, the hierarchical relation between dependent

HA-SLA: A Hierarchical Autonomic SLA Model for SLA Monitoring in Cloud Computing 115
SLAs is not considered in this research. Moreover, most
of the related works such as [7-9] followed the common
SLA structure from other environment which are not
fulfilling the cloud computing features and nature.
Most of the related works described a centralized SLA
monitoring system either in consumer, provider or
trusted party sides. These models have their own weak-
nesses. A consumer side monitoring system is proposed
in [10]. It does not have an access to provider resources
for SLA attributes assessment. On the other hand, pro-
posed framework in [11] is not completely trustful for
consumer because it was located in the provider side.
Trusted party in [12] also had a redundancy challenge
because of its tracking mechanism.
Proposed LAYSI framework in [2] and another pro-
posed model by [13] are the rare SLA monitoring sys-
tems which discuss hierarchical structure. The LAYSI
distributes the monitoring process and SLA management
through different actors of cloud computing and are not
distributed through the different SLAs. The self-adaptive
hierarchical monitoring system is proposed in [13] how-
ever also followed the common SLA structure.
According to the literature review, current cloud com-
puting environment is lacking of effective SLA structure
and SLA monitoring mechanism.
3. HA-SLA Model
In this paper, the HA-SLA model is proposed to portray
SLA structure and monitoring mechanism based on cloud
computing hierarchical nature. In this model, each SLA
could assess its attributes itself as a self-monitoring SLA.
The monitoring function is allocated in each SLA and it
will be run per each service invocation to assess the cur-
rent state of SLA. Moreover, each SLA is connected with
related SLAs in different layers of cloud computing hier-
archically as illustrated in Figure 1. Therefore, SLAs are
able to notice their monitoring results to related SLAs as
a current SLA state. The HA-SLA needs an infrastructure
to work properly in hierarchical and autonomic manner.
These features are described in subsections below.
3.1. Autonomic Feature
The HA-SLA model has an autonomic feature to provide
a self-management SLA. Current SLA includes SLA
functionalities, attributes, metrics and SLO as a simple
contract document. The HA-SLA adds some functional-
ity in SLA structure to make it as active entity rather than
passive document. So, HA-SLA is an independent self-
management SLA with embedded functions. SLA moni-
toring process is one of these functions.
In HA-SLA each SLA is able to monitor its attributes
itself. They just receive the current metrics value from
data collector then they assess the attributes state and
compare with SLO. Finally, it records the current SLA
state to the log database and notifies it to any other re-
lated SLA. The results could be used in resource man-
agement system and for any critical reactions against
violated SLA.
3.2. Hierarchical Feature
Cloud computing has a hierarchical nature and the upper
layer (UL) services relied to lower layer (LL) architec-
ture to work properly. If any service in IaaS is failed, all
upper dependent services will be failed and its SLAs will
be violated. Therefore the SLAs also rely to each other,
hierarchically. However, current SLA do not have any
relation to other related SLAs in cloud computing. The
HA-SLA builds an effective hierarchical connection be-
tween dependent SLAs in different layers of cloud com-
puting consisting of IaaS, PaaS and SaaS as illustrated in
Figure 1.
The HA-SLA enables SLAs to announce their current
states hierarchically as depicted in Figure 1. The lower
SLAs notice the current SLA attribute values to the re-
lated upper SLAs after assessment process. Finally, these
notifications could be used for current SLA attribute as-
sessing, SLA monitoring, violated SLA detecting and
resource reacting to increase the cloud computing reli-
ability.
3.3. HA-SLA Architecture
The HA-SLA cooperates with some other components in
each service provider to build a comprehensive hierar-
chical self-management SLA. Figure 2 has presented the
HA-SLA architecture from the service provider side. UL
and LL ports are the provider gates for connecting to the
related upper and lower layers SLA. At first, all SLA
features are built after negotiation process. Then,
HA-SLA is executed and receives the resource metrics
from data collector. It then records the assessed SLA
attributes in monitoring log database. Moreover the noti-
fication state is sent to related upper layer SLAs and re-
source management system for relevant decisions.
Figure 1. The hierarchical SLAs.

HA-SLA: A Hierarchical Autonomic SLA Model for SLA Monitoring in Cloud Computing
116
Figure 2. The HA-SLA architecture.
4. HA-SLA Implementation
This research developed the HA-SLA model to prove the
concept and functional workability. The HA-SLA struc-
ture includes SLA code, name, attributes, lower SLAs,
upper SLAs and emergency services as presented in Fig-
ure 3. Moreover, monitoring function is located as a part
of HA-SLA. The monitoring function invokes the attrib-
ute assessor to calculate the current value of each SLA
attributes, and gets them compared to the agreed SLO.
The attributes’ value and SLA state are then recorded in
monitoring log database, and notified to other related
SLAs in upper cloud computer layer.
5. HA-SLA Validation
An experiment has been done to validate the HA-SLA
functionality. A service throughput and response time
attributes are collected from existing dataset in [14]
which it is also used in [15,16]. These attributes are cap-
tured during the 339 invocations of the real web services.
These data are the input of developed HA-SLA as a data
collector output. The HA-SLA monitoring assesses the
attributes value based on both initial data and notified
lower layer SLA attributes value. This calculation is ac-
cording to determined metrics and formula as illustrated
in line 5 and line 6 of Figure 3. The HA-SLA monitoring
results are presented in Figure 4 and Figure 5.
The HA-SLA monitoring output for response time and
throughput attributes are depicted in Figures 4 and 5
respectively. Figure 4 has illustrated the service response
time value during the 339 invocations based on HA-SLA
monitoring system. Moreover violated SLAs which they
are more than agreed response time, 1 millisecond (ms),
are detected. Figure 5 has also presented these features
1. PublicstructAttribute
2. {
3. intcode;
4. stringname;
5. Metric[]metrics;
6. stringformula;
7. floatagreedV;
8. charagreedOperation;
9. floatcriticalV;
10. 
11. floatassessor()
12. {
13. …
14. }
15. }
16. publicstructHA_SLA
17. {
18. intcode;
19. stringname;
20. Attribute[]attributes;
21. int[]lowerSLAs;
22. int[]emergency;
23. int[]upperSLAs;
24. 
25. Notification[]Monitoring()
26. {
27. …
28. }
29. }
Figure 3: The HA-SLA struct.
Figure 4: The HA-SLA monitoring results for response
time.
Figure 5. The HA-SLA monitoring results for throughput.
for throughputs which should not be less than 20 based
on agreed SLO. Therefore the SLA attributes states are
presented by developed HA-SLA monitoring clearly.
6. Conclusions
According to the literature review, the current SLA

HA-SLA: A Hierarchical Autonomic SLA Model for SLA Monitoring in Cloud Computing
117
monitoring systems have not completely covered the
cloud computing requirements. Most of the SLA struc-
ture and monitoring systems were brought from SOA and
grid computing without enough consideration to cloud
environment hierarchical feature. In this paper, the HA-
SLA model is proposed as a hierarchical self-manage-
ment SLA. Each SLA has connected to the related SLAs
in upper and lower layer of cloud computing hierarchi-
cally. Moreover, each SLA could monitor its attributes
value itself and notify the current SLA state to the de-
pendent SLAs. The proposed model is developed and the
experiment validates the SLA structure and its monitor-
ing functionality. The effective HA-SLA reacting func-
tionality against violated SLAs will be considered in fu-
ture works.
7. Acknowledgements
This project is funded by the Exploratory Research Grant
Scheme, Ministry of Higher Education of Malaysia. Pro-
ject no.: ERGS/1/2012/TK06/UPM/02/46.
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