1. Lecturer: Eng. Mohamed Adam Isak PH.D Researcher in CS M.Sc. and B.Sc. of Information Technology Engineering, Lecturer in University of Somalia and Mogadishu university E-mail: Engmaisak@hotmail.com. Tell:0615648915 WWW.ENGMAISAK.BLOGSPOT.COM February – July 2016 SOFTWARE ENGINEERING (CS3529) TARGET CLASSES: CS14: A,B

2. Lecture 1 N.B Cloud computing section is adopted from lecturer’s M.Sc. & Ph.D. theses CHAPTER 18 – DISTRIBUTED SOFTWARE ENGINEERING & CLOUD COMPUTING

3. TOPICS COVERED BY: ENG.MOHAMED ADAM ISAK 3 Distributed systems Characteristics and Issues of D.S. Client-Server computing Cloud Computing Definition of cloud computing History of cloud computing Cloud computing deployments model Cloud computing service delivery models Benefits and limitations of cloud computing Cloud computing adoption strategy in organizations Cloud computing providers

4. DISTRIBUTED SYSTEMS BY: ENG.MOHAMED ADAM ISAK 4 Virtually all large computer-based systems are now distributed systems. “… a collection of independent computers that appears to the user as a single coherent system.” Information processing is distributed over several computers rather than restricted to a single machine. Distributed software engineering is therefore very important for enterprise computing systems.

5. DISTRIBUTED SYSTEM CHARACTERISTICS BY: ENG.MOHAMED ADAM ISAK 5 Resource sharing Sharing of hardware and software resources. Openness Use of equipment and software from different vendors. Concurrency Concurrent processing to enhance performance. Scalability Increasable upon request by adding new resources. Fault tolerance The ability to continue in operation after a fault has occurred.

6. DISTRIBUTED SYSTEM ISSUES- DESIGN ISSUES BY: ENG.MOHAMED ADAM ISAK 6 Transparency To what extent should the distributed system appear to the user as a single system? Openness Should a system be designed using standard protocols that support interoperability? Scalability How can the system be constructed so that it is scalable? Security How can usable security policies be defined and implemented? Quality of service How should the quality of service be specified. Failure management How can system failures be detected, contained and repaired?

7. CLIENT-SERVER COMPUTING BY: ENG.MOHAMED ADAM ISAK 7 Distributed systems that are accessed over the Internet are normally organized as client-server systems. In a client-server system, the user interacts with a program running on their local computer (e.g. a web browser). This interacts with another program running on a remote computer (e.g. a web server). The remote computer provides services, such as access to web pages, which are available to external clients.

8. CLIENT–SERVER INTERACTION BY: ENG.MOHAMED ADAM ISAK 8

9. CLOUD COMPUTING BY: ENG.MOHAMED ADAM ISAK 9 In Cloud Computing, the word “cloud” is used as a metaphor for "the Internet," so the phrase cloud computing means "a type of Internet- based computing," where different services - such as Servers, storage and applications - are delivered to an organization's computers and devices through the Internet. Definition of cloud computing by the European Network and Information Security Agency (ENISA): “Cloud computing is an on-demand service model for IT provision(delivery) often based on virtualization and distributed computing technologies”.

10. HISTORY OF CLOUD COMPUTING BY: ENG.MOHAMED ADAM ISAK 10 The term Cloud Computing was first mentioned in 1999 for business purposes when www.salesforce.com introduced its business applications. Major online retailer www.amazon.com followed in 2002 when it provided its cloud based storage services, followed by Amazon Elastic Cloud Computing (EC2) in 2006 for small businesses. During this time several cloud applications and services from various companies, such as Microsoft and Google as well as Force.com and Amazon were developed. Adopted from: Withee, K., & Reed, J. (2012). Office 365 for Dummies John Wiley New Jersey U.S.A.

11. CLOUD COMPUTING – DEPLOYMENT MODELS BY: ENG.MOHAMED ADAM ISAK 11 1.PUBLIC CLOUD: Cisco defines public cloud as cloud infrastructure shared or accessible by all, with applications and services delivered through the Internet. 2.PRIVATE CLOUD: Cisco defined private cloud as restricted cloud infrastructure operated by or on behalf of a specific organization, available exclusively to approved users affiliated with that organization; cloud services are delivered using a private network. 3.COMMUNITY CLOUD: Cisco defined community cloud as multitenant, private cloud infrastructure that supports a specific community, consisting of two or more organizations. 4.HYBRID CLOUD: Cisco defined Hybrid cloud as combination of two or more of the preceding cloud types.

12. CLOUD SERVICE MODELS BY: ENG.MOHAMED ADAM ISAK 12 1.Software as a Service (SaaS): Provides users to use the applications online. Examples: Mail, SkyDrive, Amazon Cloud Drive… etc. 2.Platform as a Service (PaaS): To control the hosting environments to specific needs. Ex: Google App Engine to deploy and dynamically scale Python and Java based web applications. 3.Infrastructure as a Service (IaaS): Provides basic infrastructure components such as CPU, memory and storage. Ex: Amazon’s Elastic Compute Cloud (EC2).

13. ADVANTAGES OF CLOUD COMPUTING BY: ENG.MOHAMED ADAM ISAK 13 Khajeh-Hosseini et al. (2010) conduct a large number of interviews with stakeholders who decide in favour of organisational Cloud adoption. They perform stakeholder analysis and summarise benefits and risks arriving at top ranking factors as follows. Here are the benefits: 1.Improve satisfaction of work 2.Opportunity to develop new skills 3.Opportunity for organisational growth 4.Opportunity to offer new products/services 5.Improved status Opportunity to manage income and outgoings Adopted from: Khajeh-Hosseini, A., Greenwood, D., and Sommerville, I., “Cloud Migration: A Case Study of Migrating an Enterprise IT System to IaaS”, 3rd IEEE International conference on Cloud Computing, Cloud 2010, 5-10 July 2010; Miami, USA (Khajeh-Hosseini et al., 2010 a).

14. LIMITATIONS OF CLOUD COMPUTING BY: ENG.MOHAMED ADAM ISAK 14 Here are the Risks: 1.Lack of supporting resources 2.Lack of understanding of the Cloud 3.Departmental downsizing Uncertainty with new technology 4. Weakening of customer care and service quality 5.Increased dependence on third parties 6.Decrease of satisfying work Adopted from: Khajeh-Hosseini, A., Greenwood, D., and Sommerville, I., “Cloud Migration: A Case Study of Migrating an Enterprise IT System to IaaS”, 3rd IEEE International conference on Cloud Computing, Cloud 2010, 5-10 July 2010; Miami, USA (Khajeh-Hosseini et al., 2010 a).

15. CLOUD ADOPTION STRATEGY IN THE ORGANIZATIONS BY: ENG.MOHAMED ADAM ISAK 15 Developing the knowledge base about Cloud Computing; Evaluating the present stage of the organization. Experimenting the Cloud Computing solutions Choosing the cloud computing solution Implementation &management of the Cloud Computing solution Mircea, M., & Andreescu, A. I. (2011). Using Cloud Computing in Higher Education: A Strategy to Improve Agility in the Current Financial Crisis.

16. CLOUD PROVIDERS BY: ENG.MOHAMED ADAM ISAK 16 Google Microsoft Amazon Dropbox SugarSync Apple

17. KEY POINTS BY: ENG.MOHAMED ADAM ISAK 17 The benefits of distributed systems are that they can be scaled to cope with increasing demand, can continue to provide user services if parts of the system fail, and they enable resources to be shared. Issues to be considered in the design of distributed systems include transparency, openness, scalability, security, quality of service and failure management. Client–server systems are structured into layers, with the presentation layer implemented on a client computer. Servers provide data management, application and database services. Cloud computing is an on-demand service model for IT provision(delivery) often based on virtualization and distributed computing technologies.