[Virtualization] Introduction

A piece of software that manages and virtualizes hardware for applications
– An indirection layer between applications and hardware
– Provides a high-level interface to applications
– While interact with hardware devices with low-level interfaces
– Runs privileged instructions to interact with hardware devices
Applications
– Can only execute unprivileged instructions
– Perform system calls or faults to “trap” into OS
– OS protect applications from each other (to some extent) (e.g., address space)

Adding another level of indirection to run OSes on an abstraction of hardware
Virtual Machine (Guest OS)
– OS that runs on virtualized hardware resources
– Manages by another software (VMM/Hypervisor)
Virtual Machine Monitor (Hypervisor)
– The software that creates and manages the execution of virtual machines
– Runs on bare-metal hardware

Mainframes and IBM

Issues with Early Mainframes

Different generations were not architecturally compatible
Batch-oriented (against interactive)
Meanwhile, ideas started to appear towards a time-sharing OS
The computer was becoming a multiplexed tool for a community of users, instead of being a batch tool for wizard programmers

IBM’s Response

IBM bet the company on the System/360 hardware family [1964]
– S/360 was the first to clearly distinguish architecture and implementation
– Its architecture was virtualizable
The CP/CMS system software [1968]
– CP: a “control program” that created and managed virtual S/360 machines
– CMS: the “Cambridge monitor system” — a lightweight, single-user OS
– With CP/CMS, can run several different OSs concurrently on the same HW
IBM CP/CMS is the first virtualization systems. Main purpose: multiple users can share a mainframe

IBM’s Mainframe Product Line

System/360 (1964-1970)
– Support virtualization via CP/CMS, channel I/O, virtual memory, …
System/370 (1970-1988)
– Reimplementation of CP/CMS as VM/370
System/390 (1900-2000)
zSeries (2000-present)
Huge moneymaker for IBM, and may business still depend on these!

PCs and Multi-User OSes

1976: Steve Jobs and Steve Wozniak start Apple Computers and roll out the Apple I, the first computer with a single-circuit board
1981: The first IBM personal computer, code-named “Acorn,” is introduced. It uses Microsoft’s MS-DOS
1983: Apple’s Lisa is the first personal computer with a GUI
1985: Microsoft announces Windows
The PC market (1980-90s): ship hundreds of millions of units, not hundreds of units
Cluster computing (1990s): build a cheap mainframe out of a cluster of PCs

Multiprocessor and Stanford FLASH

Development of multiprocessor hardware boomed (1990s)
Stanford FLASH Multiprocessor
– A multiprocessor that integrates global cache coherence and message passing
But system software lagged behind
Commodity OSes do not scale and cannot isolate/contain faults

Stanford Disco and VMWare

Stanford Disco project (SOSP’97 Mendel Rosenblum et al.)
– Extend modern OS to run efficiently on shared memory multiprocessors
– A VMM built to run multiple copies of Silicon Graphics IRIX OS on FLASH
Mendel Rosenblum, Diane Greene, and others co-founded VMWare in 1998
– Brought virtualization to PCs. Main purpose: run different OSes on different architectures
– Initial market was software developers for testing software in multiple OSes
– Acquired by EMC (2003), which later merged with DELL (2016)

Server Consolidation

Datacenters often run many services (e.g., search, mail server, database)
– Easier to manage by running one service per machine
– Leads to low resource utilization
Virtualization can “consolidate” servers by hosting many VMs per machine, each running one service
– Higher resource utilization while still delivering manageability

The Cloud Era

The cloud revolution is what really took virtualization on
Instead of renting physical machines, rent VMs
– Better consolidation and resource utilization
– Better portability and manageability
– Easy to deploy and maintain software
– However, raise certain security and QoS concerns
Many instance types, some with specialized hardware; all well maintained and patched
– AWS: 241 instance types in 30 families (as of Dec 2019)

The Virtuous Cycle for Cloud Providers

Container

VMs run a complete OS on emulated hardware
– Too heavy-weighted and unnecessary for many cloud usages
– Need to maintain OS versions, libraries, and make sure applications are compatible
Containers (e.g., Docker, LXC)
– Run multiple isolated user-space applications on the host OS
– Much more lightweight: better runtime performance, less memory, faster startup
– Easier to deploy and maintain applications
– But doesn’t provide as strong security boundaries as VMs

Managing Containers

Need a way to manage a cluster of containers
– Handle failure, scheduling, monitoring, authentication, etc.
Kubernetes: the most popular container orchestration today
Cloud providers also offer various container orchestration service
– e.g., AWS ECS, EKS

Serverless Computing

VMs and containers in cloud still need to be “managed”
Is there a way to just write software and let the cloud do all the rest?
Serverless computing (mainly in the form of Function as a Service)
– Autoscaled and billed by request load
– No need to manage “server cluster” or handle failure
– A lot less control and customization (e.g., fixed CPU/memory/memory ratio, no direct communication across functions, no easy way to maintain states)

Summary of Virtualization History

Byung Hoon Ahn