is451finalquickreview

-the creation of substitutes for real resources – abstraction of real resources

-Ex. SAN, VLAN, RAID

• -Portable virtual machines
• -Consolidation of resources
• -Isolation of virtual machines

-applications run faster

-the process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network.

-is the pooling of physical storage from multiple network storage devices into what appears to be a single storage device that is managed from a central console. 

• -A virtual machine is a tightly isolated software container that can run its own operating systems and applications as if it were a physical computer.
• -On a given h/w platform (host) – simulated (virtual) machine environments are created

• -consolidation to reduce hw costs
• -workloads consolidation
• -single consolidated view/management
• -portability of virtual machines
• -can be used for testing/training

-Is sharing of physical resources (servers, storage, network) as a dynamic resource pool

• -Type 2 hypervisor
• -host O/S runs virtualization software, unmodified guest O/Ss run isolated from each other (separate virtual machines)
• -Additional resources are required for host O/S

• -(type 1 hypervisor)
• - there’s no host O/S. Virtual machines run on top of type 1 hypervisor directly on a hardware platform
• -No resources are wasted for a Host O/S
• -Higher virtualization efficiency can be achieved

• -Guest O/S is modified to include a call to hypervisor to access h/w resources
• -Guest O/S is “aware” of running in a virtualized environment
• -Makes the structure of hypervisor simpler
• -May make virtual machine more efficient

-Guest OS is modified

-Refers to the process of allowing each guest operating systems run unmodified in isolation

-Guest OS privileged instructions expect to run in Ring 0

-Modifying a CPU to include extended set of instructions

-It complements it for more efficiency

-a software switch as part of the hypervisor

-switching function performed by an external switch

-Dynamically scalable, device-independent and task-centric computing resources are provided online, with all charges being on a usage basis.

• -Apps (s/w), processing power and storage (h/w) accessed on the Internet, online
• -Task-centric computing
• -Device/platform independent computing
• -Dynamically scalable, on-demand computing
• -Resources are available with variable, per-usage costs (not fixed)

• -Pay-per-use resources
• -Accessible from most devices
• -Promotes collaboration

-Faster access

• -A User creating a Facebook application
• -A user accessing a Yahoo email account
• -A user accessing a supplier's virtual server to test an application
• -Not an example
• --A user accessing his email account on their company's email server

• -Software as a Service (Saas)
• -Running existing online applications.
• -Online productivity tools, including word processing, spreadsheet, presentation: GoogleDocs, Zoho, Microsoft)
• -creative web tools - Pixlr, Jaycut, Aviary
• -dedicated business applications: Salesforce, Employease, NetSuite .
• -Available for free or as a subscription service, accessible from any Internet client, facilitate collaboration.
• -The disadvantage is that they are not customized enough, too generic.

-Example of SaaS

• -Platform as a Service (Paas)
• -Environment and a set of tools to create online applications,
• -Allows quick development of applications without much additional cost.
• -Can deploy applications privately or publicly.
• -Limits developers to an existing set of tools and languages and platform dependency.

-Example of PaaS

• -Infrastructure as a Service (Iaas), sometimes known as Hardware as a Service (Haas).
• -Allows a business to run their own applications on the cloud hw without investing in its own hw infrastructure.
• -Cloud suppliers can use actual physical or virtual servers to host applications.

-private, dedicated, hybrid and cloud hosting

-(certain physical servers are dedicated to one customer)

-(customer rents physical servers on demand as needed)

-(a mix of physical and virtual servers to reduce cost and increase flexibility)

-(customer rents virtual servers on demand as needed, sometimes hourly).

• -Availability
• -Privacy
• -Data theft/loss
• -Security

• -Temporary storage of frequently accessed data (duplicating original data stored somewhere else)
• -Reduces access time/latency for clients
• -Reduces bandwidth usage
• -Reduces load on a server

-for a single user

-same principle for multiple users

• -Cache located closer to the client
• -Usually deployed by an ISP
• -Decreases bandwidth usage (ISP to the Internet link in the example below)

• -Aka gateway proxy or web accelerators
• -Cache proxy located closer to the origin web server
• -Usually deployed by an Web hosting ISP
• -Decreases load on the web server
• -Several reverse proxy caches implemented together can form a Content Delivery Network

-how long the document stays “fresh” or can be used from cache without rechecking the origin server

-[seconds] — specifies the maximum amount of time that an representation will be considered fresh.

-tells all caches how long the associated representation is fresh for

• – compare the cached document to the origin document once it’s not “fresh” anymore
• -Are used by caches to compare the cached document to the original document for changes
• -If validator is not present and no freshness information is available, the document won’t be cached

-the last time that the document last changed

-unique identifiers that generated by the server and changed every time the representation does

• – done by switches/routers, clients are unaware
• -To avoid configuring each client to point to cache proxy
• -Can be accomplished using inline cache, layer 4 switch, WCCP, policy-based routing
• -Cache pretend to be the origin server, tricks client into thinking it's connected to the server

• -Network of computers that deliver content on the web.
• -Content pushed-out/delivered “closer” to the clients
• -Designed to improve Internet performance (i.e. decrease latency for clients, decrease bandwidth use)
• -Consists of origin server, surrogate (edge servers)
• -Caching and server load balancing techniques are used
• -ESI (Edge-Side Includes) – open standard markup language to augment HTML for help with dynamic delivery and assembly of Web documents

• -Designed to improve Internet performance
• -(i.e. decrease latency for clients, decrease bandwidth use)