Database Reference
In-Depth Information
Cloud
consumers
Cloud service
providers
(CSP)
End users
A-SLA
I-SLA
e.g., Software-as-a-Service (SaaS)
Cloud-hosted software applications
e.g., Amazon, Microsoft,
Google, Rackspace
FIGURE 11.1
SLA parties in cloud environments.
Figure 11.1 illustrates the relationship between I-SLA and A-SLA in the soft-
ware stack of cloud-hosted applications. In practice, traditional cloud monitoring
technologies (e.g., Amazon CloudWatch*) focus on low-level computing resources
(e.g., CPU speed, CPU utilization, disk speed). In principle, translating the SLAs
of applications' transactions to the thresholds of utilization for low-level computing
resources is a very challenging task and is usually done in an ad hoc manner due to
the complexity and dynamism inherent in the interaction between the different tiers
and components of the system. In particular, meeting SLAs that are agreed with end
users by consumer applications of cloud resources using the traditional techniques
for resource provisioning is a very challenging task due to many reasons such as the
following:
• Highly dynamic workload : An application service can be used by large
numbers of end users and highly variable load spikes in demand can occur
depending on the day and the time of year, and the popularity of the appli-
cation. In addition, the characteristic of workload could vary significantly
from one application type to another and possible fluctuations on the
workload characteristics that could be of several orders of magnitude on
the same business day may occur [3]. Therefore, predicting the workload
behavior (e.g., arrival pattern, I/O behavior, service time distribution) and
consequently accurate planning of the computing resource requirements
are very challenging tasks.
• Performance variability of cloud resources : Several studies have reported
that the variation of the performance of cloud computing resources is
high [6,18]. As a result, currently, cloud service providers do not provide
adequate SLAs for their service offerings. Particularly, most providers
guarantee only the availability (but not the performance) of their services
[2,8].
Uncertain behavior : One complexity that arises with the virtualization
technology is that it becomes harder to provide performance guarantees
* http://aws.amazon.com/cloudwatch/.
Search WWH ::




Custom Search