Mobycast

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Summary

Cloud computing would not be possible if not for virtual machines. They are the fundamental resource for cloud-native applications. Then along came Docker with its containers, and the virtualization scene got a bit more complicated and confusing.

So, we kicked off a new series where we go deep on virtual machines and containers, aiming to clear up any confusion between these important technologies.

In episode #81 of Mobycast, we discussed full virtualization, also known as virtual machines. We explained hypervisors, the fundamental technology that enables virtual machines. And then we took a detailed look at how Type 1 hypervisors work.

In today's episode of Mobycast, Jon and Chris bring these concepts to life by examining several popular hypervisor implementations.

Show Notes

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Show Details

In this episode, we cover the following topics:
  • Hypervisor implementations 
    • Hyper-V 
      • Type 1 hypervisor from Microsoft 
      • Architecture 
        • Implements isolation of virtual machines in terms of a partition 
          • Partition is logical unit of isolation in which each guest OS executes 
        • Parent partition 
          • Virtualization software runs in parent partition and has direct access to hardware 
            • Requires supported version of Windows Server 
          • There must be at least one parent partition 
          • Parent partition creates child partitions which host the guest OSes 
            • Done via Hyper-V "hypercall" API 
          • Parent partitions run a Virtualization Service Provider (VSP) which connects to the VMBus 
            • Handles device access requests from child partition 
        • Child partition 
          • Does not have direct access to hardware 
            • Has virtual view of processor and runs in Guest Virtual Address (not necessarily the entire virtual address space) 
          • Hypervisor handles interrupts to processor, and redirects to respective partition 
          • Any request to the virtual devices is redirected via the VMBus to the devices in the parent partition 
        • VMBus 
          • Logical channel which enables inter-partition communication 
    • KVM (Kernel-based Virtual Machine) 
      • Virtualization module in Linux kernel 
        • Turns Linux kernel into hypervisor 
        • Available in mainline Linux since 2007 
      • Can run multiple VMs running unmodified Linux or Windows images 
      • Leverages hardware virtualization 
        • Via CPU virtualization extensions (Intel VT or AMD-V) 
      • But also provides paravirtualization support for Linux/FreeBSD/NetBSD/Windows using VirtIO API 
      • Architecture 
        • Kernel component 
          • Consists of: 
            • Loadable kernel module, kvm.ko, that provides the core virtualization infrastructure 
            • Processor specific module, kvm-intel.ko or kvm-amd.ko 
        • Userspace component 
          • QEMU (Quick Emulator) 
            • Userland program that does hardware emulation 
            • Used by KVM for I/O emulations 
  • AWS hypervisor choices & history 
    • AWS uses custom hardware for faster EC2 VM performance 
    • Original EC2 technology ran highly customized version of Xen hypervisor 
      • VMs can run using either paravirtualization (PV) or hardware virtual machine (HVM) 
      • HVM guests are fully virtualized 
        • VMs on top of hypervisor are not aware they are sharing with other VMs 
      • Memory allocated to guest OSes is scrubbed by hypervisor when it is de-allocated 
      • Only AWS admins have access to hypervisors 
    • AWS found that Xen has many limitations that impede their growth 
      • Engineers improved performance by moving parts of software stack to purpose-built hardware components 
    • C3 instance family (2013) 
      • Debut of custom chips in Amazon EC2 
        • Custom network interface for faster bandwidth and throughput 
    • C4 instance family (2015) 
      • Offload network virtualization to custom hardware with ASIC optimized for storage services 
    • C5 instance family (2017) 
      • Project Nitro 
        • Traditional hypervisors do everything 
          • Protect the physical hardware and bios, virtualize the CPU, storage, networking, management tasks 
        • Nitro breaks apart those functions, offloading to dedicated hardware and software 
        • Replace Xen with a highly optimized KVM hypervisor tightly coupled with an ASIC 
        • Very fast VMs approaching performance of bare metal server 
    • Amazon EC2 – Bare metal instances (2017) 
      • Use Project Nitro 
Links

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For a full transcription of this episode, please visit the episode webpage.

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What is Mobycast?

A Podcast About Cloud Native Software Development, AWS, and Distributed Systems