EBU6502_cloud_computing_notes/1-2-sla-virtualization.md

SLA and Virtualization

SLA

Definition

• Service Level Agreement: a service-based legal agreement between a provider and a subscriber
• Accepted before a cloud service can be used
• Content
  • Provider's responsibility
  • Subscriber's responsibility, and entitlements
  • Billing and accounting system

Types

• Service based SLA:
  • Offer shared resources, used by many customers
  • Offered to cloud users
• Customer based SLA
  • Agreement between individual customer or group, to provide non-shared specific services
• Multi-level SLA:
  • Corporate level: generic and cover all user of an organization
  • Customer level: specific group of user
  • Service: specific type of service

Boundaries

• Organizational boundary
  • Physical perimeter, owned and governed by organization or cloud provider
• Trust boundary
  • When cloud user extend trust beyond its physical boundary, and include resources from the cloud

Characteristics of cloud

• On-demand usage: use more cloud resources only when they need it
• Multi-tenancy aka. Resource pooling: Resources are instances that can be used by many users
• Scalability: Able to automatically scale up or down based on the settings and agreements
• Ubiquitous access: Can be accessed everywhere with lots of devices
• Measured usage: keep track and record the amount of IT resources used by consumers
  • Used for accounting and auditing
• Resilience: distribute and replicate resources to provide redundancy, and fail over mechanism

QoS

• SLA is based on Quality of Service
• Combination of metrics relating to requirements, and satisfaction of services offered by a provider.
• Quantitative or qualitative
• Parameters:
  • Reliability availability
  • Security and trust
  • Scalability
  • Data integrity and data protection
  • Resilience
  • Data recovery time
  • Support

Virtualization

Definition

• The process of creating the virtual version of hardware, database, operating system and application from real copies, using virtual machine monitor to emulate the physical functionalities.
• Multiple virtual machines are multiplexed in to the same hardware, to serve as an abstraction of physical OS
• Guest OS is not bound to the physical hardware.
• Guest OS runs on host OS, and they can be different

Levels of virtualization

• Instruction Set Architecture level: ISA emulation, which is used to run many legacy codes written for a different hardware configuration, like Dynamo
• Hardware level: VMs are located directly on top of hardware, allows the virtualization of each of the hardware components, which could be the input-output device, the memory, the processor, etc, like VMWare
• Operating system level: an operating system (OS) virtualization paradigm in which the kernel allows the existence of multiple isolated user space instances, like Jails
• Library level: translate API calls to user libraries, like vCUDA
• Application level: allows high-level language programs to be compiled easily. java's jvm

Types of Virtualizations

• Desktop: Create desktop computer from physical desktop machine
• Hardware: Virtual computer with OS that represents and act as a real physical computer.
• Nested virtualization: Virtual machine inside another one
• CPU virtualization: Virtual CPU are created to reduce stress on host
• Memory virtualization: virtual memory is created and run on the VM, controlled by the virtual CPU of VM, but can't access memory address outside virtual
• IO virtualization: Route IO request between virtual devices and physical hardware

Virtual clusters

• Physical cluster: interconnected by physical network
  • Failure may cause a falling physical node
• Virtual cluster: VMs intereconnected by a virtual network across several physical networks
  • Node can be either physical or virtual
  • Cluster VMs can run different OS
  • To enhance utilization and flexibility
  • Can be freely replicated, and is fault tolerant easy to recover
  • Nodes can grow or shrink
  • Failure won't cause shutdown to host machine

Migration of VM

Introduction

• VM can be moved from one cluster to another, which isn't possible with physical hosts.
• Four ways:
  • Guest-based manager, where cluster manager is in guest vm
  • Host based manager: supervises the guest system, and can restart guest system remotely
  • Independent cluster manager on both host and guest
  • Use integrated cluster manager

Six (five) steps of VM migration

• Start migration (for some reason this is counted as step 0 and 1???)
  • Determine VM to migrate
  • Determine destination host
• Transfer memory
  • State is stored in memory, so transfer memory first
• Suspend VM and copy remaining data
  • Execution is suspended when last memory is transfered.
  • Non memory components like network and cpu are sent to destination
• Commit
  • After all data, VM reloads and continue execution
• Activate
  • Network is redirected to new VM
  • remove the original VM from source host

Mechanism for cloud infra: building blocks

• Environment:
  • Logical network perimeter: Virtual network boundary, encompass and isolate a group of resources, that may be physically distributed., to isolate cloud resource from unauthorized users
  • Virtual Server: behaves exactly like a physical one, and running on the same physical server which is shared by multiple cloud users
  • Resource replication: create multiple of same resource to various locations, physically distributed around the world.
  • Ready made environment: provided by PaaS (platform as a service)
  • Failover system: use clustering to provide redundancy
  • Hypervisor: generate virtual server instances
  • Multi device broker: converts and exchanges information
  • Resource cluster: cloud resources are geographically distributed and group resources and instances together
  • State management database, used to temporarily maintain state data for software programs to improve performance.
• Scaling
  • Automated Scaling listener: monitors communication between consumers and services for dynamic scaling up or down.
  • Load balancer: cloud runtime mechanism that distributes workload: data processing, computation, network traffic across two or more cloud resources, for better performance( automated horizontal scaling)
• Monitoring
  • Cloud usage monitor: Autonomous software used for collecting and processing cloud resource usage data.
  • SLA monitor: monitors the performance to ensure they are fulfilling the Quality of Service requirement
  • Pay per use monitor: monitor the usage and calculate the price according to the agreement
  • Audit monitor: track data for network, to confirm to regulatory obligation

Different hypervisors

Microsoft virtualization technology

• parent partition: logical hard drive for running hypervisor layer, and nesting child partitions
• Child partitions: Logical hard drive responsible for running isolated OSes
• Virtualization stack Collections of resources including the hypervisor, which makes up the Microsoft hyper V
• Virtualization service provider: parent partition side, server that handles IO
• Virtualization child provider: child partition component, that sends request to VSP
• VMBus: send requests and data between VMs
• WMI: Windows management instrumentation, manages virtual devices
• Windows kernel: manages IO request from parent and child
• IHV: hardware drivers
• VM worker process: run and configure one VM each
• Hypervisor
  • Manages a minimum set of hardware components
  • Isolate component, to enhance loose coupling
  • Provide security
  • Enhance performance
• 

Xen Virtualization Technology

• 
• Host Hardware: real hardware
• Xen Hypervisor: lean software layer, that runs on host hardware and manages the CPUs, memory, IO devices
• Guest Domains / Virtual Machines
• Control Domain, or domain 0: special virtual machine with privilege to access, and handles IO functions and VM's interactions
• Toolstack: control stack on domain 0, enables user to manage virtual machines

Virtualization Technologies

• host components: real hardware
• guest components: virtual system created from host machine, includes os, network, databases and servers
• Hypervisor, or virtual machine manager: manages virtual machines
• Networking technologies
• Web services: manager over the internet
• Front end systems: interface between user and virtual machine

Advantages and challenges

Advantages:

• Deployment:
  • Less cost, reduction in cost of hardware, energy, cooling , expertise and administration
  • Less time needed
  • Creating servers on different system is easy
• Maintainence:
  • Scalability
  • Efficiency
  • Reliability
  • Fast data disaster recovery
  • Backups and migrations are easy

Challenges

• Security of virtual machines
• Need expertise to manage virtual machines
• Reliant back up systems are needed
• Failures of host will affect the guest system.
• Performance may not be as good as using physical ones

Future of Virtualization

• Is and will be the dominant component of cloud computing
• Decoupling of application will increase
• Less energy consumption by optimizing OS and VMM
• Dominant in IT market
• Even more scalable
• Better security

Major classes of hardware virtualization

Full virtualization, Hardware virtual machine

• Complete simulation of actual hardware, so that OS and software doesn't need any modifications.
• AWS Support
  • HVM AMI (Amazon Machine Images), in a fully virtualized environment
  • Can run OS without modification
  • HW extension is support
  • Instance type support: all current
  • Regioin: all

Paravirtualization

• Allows guest applications to be executed, as if they are running on a separate system, but hard ware environment is not simulated
• Guest need to be modified
• AWS Support
  • PV AMI: special bootloader is used
  • Can run on host hardware without explicit support for virtualization
  • Hardware extention is not supported
  • Some instance types are supported
  • Some regions are supported

Layering and Virtualization

Layering

• Definition: approach to manage system complexity
• Goals:
  • Simplify description of subsystem, to abstract through interface
  • Minimize interaction between subsystems
  • Enable us to independently manage each subsystem
• Layering in computers:
  • Hardware
  • Software
    • OS
    • Library
    • Applications

Interfaces in virtualization

• ISA (Instruction Set Architecture): Instruction Set Architecture: boundary between hardware and software
• ABI (Application Binary Interface): Allow application and library modules to access hardware, invokes system calls
• API (Application Program Interface): Is a set of rules or protocols that enables software applications to communicate with each other to exchange data, features and functionality