DistributedSystemLearn/ServersAndVirtualization.md at master · unlimitediw/DistributedSystemLearn

Topic 1: Server

Infrastructure as a Service(IaaS)
- Greate flexibility for cloud user and Less management handled by cloud operator
- Virtual Machines
  - Virtualization is used to split up a physical server
    - Allows multiple customers to share one machine.
    - Simplifies management since VMs are not strictly tied to HW.
    - Provdes isolation between cloud users.
Platform as a Service
- e.g: Google App Engine, Heroku and Amazon EMR
- The cloud provides a programming platform
- Typically used to run highly scalable web apps
- Cloud users write applications to run on the cloud
  - Must write code to meet cloud API
  - Cloud automatically scales the application based on demand
  - Provides much greater scalability, but program must be specially written
Software as a Service
- The cloud provides a piece of software e.g: email, office, project management, customer relations, supply chain, etc ( Dropbox, icloud and GMail)
- Provides even greater scalability
  - Entire cloud infrastructure is devoted just to one particular type of application
  - Customer: cheaper and simpler, Provider: economy of scale
Cloud Computing Goals
- Offer fast services to customers worldwide
  - Need geographic diversity and high scalability
  - Low latency requests: fast responses
  - High throughput: simultaneous processing
- Highly reliable and secure
  - Servers crash
  - Data center lose power
  - Malicious users can attack
- As cheaply as possible
  - Users expect services for free
  - Cloud needs to pay for servers, cooling infrastructure, energy, system adminstrators, etc

Topic 2: Virtualizing Resources

VM
- Type of Virtualization:
  - Application Virtualization
    - Runs application code
    - Java JVM, WINE
  - Hosted Virtualization
    - Virtualizes a full OS and apps
    - VMware Player, Virtual Box
  - Paravirtualization
    - Modify OS to simplify hypervisor
    - Xen
  - Full Virtualization
    - Runs directly on HW
    - VMware, ESXi
- Pros of VM:
  - Consolidation
    - Can spilt a physical server to many smaller servers
  - Security
    - VMs are isolated from one another
  - Resource management
    - Can dynamically adjust a VM's CPU and memory share
  - Convenience
    - VM is abstracted away from physical hardware
    - Great for development
- Process
  - Virtualization layer replaces an interface
  - Must intercept calls and translate them
    - Java - intercept/compile code to match host
    - Hosted VM - translate system calls for host OS
    - Full Virtualization - trap on sensitive instructions
  - Allocate resources
    - VMs must share memory and CPU time
  - Handle I/O
    - Abstraction layer separates VM from physical hardware
- Hosted Virtualization
  - Normal OS divided into Kernel and User modes
  - Protected instructions only work in kernel mode
    - I/O, memory allocation, etc
    - Traps to kernel if run in user mode
  - CPU Rings
    - Modern CPUs support multiple protection rings
      - Ring 0 = kernel mode
      - Ring 3 = user mode
      - Ring 1-2 = drivers or unused, hosted virtualization VM OS
  - Dynamic translation
    - Preprocess all code being run by the OS indside the VM
    - Detect sensitive instructions
    - Repackage and call into parent OS
    - Return result to guest OS
- Full Virtualization'
  - Characteristics
    - Hypervisor runs directly on hardware in Ring 0
    - Manages VMs
    - Uses dynamic translation to rewrite protected instructions
    - Host device drivers for VMs
  - HW Virtualization
    - Some CPUs have support for virtualization
      - AMD-V, Intel-VT
    - Provides an extra ring for running a hypervisor
      - Protected instructions in VM OS are trapped an passed to Ring -1(Hypervisor)
- Hosted and Full virtualization are VM OS agnostic
  - Guest OS does not know it is being virtualized
  - Translate binary code(slow)
  - Get help from hardware(expensive)
  - Guest OS can help with device drivers
- Paravirtualization in Xen
  - Modifies Linux so that it is virtualization aware
  - OS asks hypervisor for help to run special instructions
  - Driver VM is special management VM
    - Starts/stops VMs
    - Contains Linux device drivers
  - Very simple hypervisor(Xen hypervisor)
    - Reduces overhead
    - No need for HW virtualization
- Trade-offs
  - Hosted Virtualization
    - easier to install, and turn off, great for testing/ development
    - neg: fewer resources available, because need host OS
  - Full Virtualization
    - With or without HW assist
    - Strong isolation
    - greater performance than hosted, better scalability
    - neg: needs drivers for all HW
  - Paravirtualization
    - neg: VM is aware it is in a virtual environment(security)
    - need to modify OS
- Virtualizing Memory
  - System's memory must be shared by all VMs
  - Page Tables
- Container
  - Properties
    - Processes
      - OS provides isolation
    - Isolated
      - Memory
      - File system
      - Network
      - Devices
    - Shared
      - OS Kernel
  - Multi-process containers
    - Can run multiple processes in the same container group
  - Resources
    - Can assign CPU weights and memory limits for each group
  - Shared Kernel
    - Page tables (memory)
    - Scheduler (CPU)
    - Networking stack
    - File system virtualization
  - Distro vs Kernel
    - Kernel = core operating system functionality
    - Distribution = collection of software and kernel
  - Containers and Distros
    - Each container can have its own distribution
    - Must share the same host kernel
  - Container Packaging
    - Deployment - big benefit of containers/virtualization
      - Lets you package up an application and all of its requirements
      - Evem the distribution and 3rd party utilities
      - Very helpful for system administrators
  - Container 'image'
    - Linux distribution base files
    - Dependency libs/utils
    - Configuration files
    - Application to run
  - Can inerit files/libraries from host to reduce size of the container package
  - File System Virtualization
    - Container's file system is built by layering
      - Several containers can use the same file system layers
    - Read/Writer
      - Allow multiple containers to manipulate data on host file system
    - Copy on Write
      - Each container thinks it has its own version of the file system
      - Only duplicate the specific files that are written to
  - Container vs VMs
    - Container Pros
      - lightweight
      - less resource consumption
      - easier to deploy
      - specify resources just for application
      - startup time
    - VMs pros
      - stronger isolation
      - different kernel versions/ OSes
      - fault tolerance/isolation
      - combine with containers
  - Containers + VMs
    - Containers can be combined with virtualization tools
    - Docker on Windows
      - Lets you run windows containers using OS isolation tools
      - Lets you run linux containers by starting a linux VM automatically for you and dividing it up into containers
  - Challenges
    - Heterogeneity: Different HW, SW, workloads
      - HW
        
        different processor architecture, memory, number of CPUs, location disks etc
        
        for Iaas users need to know what they will get
        
        for Paas/Saas we can hide this
      - Workloads
        
        stress out hardware, need to spread request(load balancing)
        
        can also help us share resources if peak are at different times
      - SW
        
        need to worry about compatibility
        
        affects interoperability
    - Openness: interoperability, shared protocols
      - Ranking of openness/flexible: VMs in my data center > IaaS > Containers > Paas > Saas
    - Security: confidentiality, integrity, availability
      - VMs most secure, most control
      - Containers kernel is shared, so less isolation
      - Cloud: Trust? more skilled at providing security?
    - Failure Handling: crashes, bugs, malicious
      - Iaas with Containers/VMs
        
        physical failures can bring them all down
        
        bugs and attacks with user
      - PaaS/SaaS
        
        cloud needs to worry about bugs in their platform and malicious attacks
      - Containers are less isolated than VMs
        
        fault in the kernel will bring down all containers
    - Concurrency: parallelism, consistency
      - Depends on SW runing VMs/containers
      - IaaS: depends on users
      - PaaS/Saas: cloud provider must handle concurrency so they limit the type of state you can have to simplify consistency
    - When running multiple VMs, need to worry about scheduling on CPUs
      - Kernel knows about all processes in a container, but sees the VM as a black box
    - Quality of Service: latency, throughput
      - QoS depends on applications
      - Containers are lighter weight so should have better QoS
      - Qos affected by available HW and workload distribution
      - Tail latency: highly affected by shared resources
        
        cache misses will have big impact
        
        includes network costs
    - Scalability: performance gain with more resources
      - SaaS has easiest scalability since it has full control
      - IaaS harder to scale
        
        User can ask for resources
        
        Cloud can monitor and respond
      - Containers are more scalable because lighter weight
        
        we have great control over how resources are being used
    - Transparency: abstraction layers, interfaces
      - IaaS exposes HW interface
      - PaaS exposes software library interface
      - SaaS exposes user interface for software
      - Data transparency -> storage details hidden from us
      - Logic transparency -> affects what SW we can run

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Topic 1: Server

Topic 2: Virtualizing Resources