Xen实战指南：系统管理员必备

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"The Book of Xen 是一本由Chris Takemura和Luke S. Crawford合著的实践指南，专门针对系统管理员，全面介绍Xen虚拟化技术的完整PDF版本。" Xen是一个开源的虚拟化平台，它允许在一个物理硬件上运行多个操作系统实例，每个实例被称为一个域（Domain）。这本书深入浅出地探讨了Xen虚拟化技术，对于想要理解和管理Xen环境的系统管理员来说是一份宝贵的资源。书中可能涵盖了以下关键知识点： 1. **Xen的基本概念**：解释Xen架构，包括主要组件如控制域（Dom0）——这是具有直接访问硬件权限的特殊虚拟机，以及客户域（DomU）——通常运行用户的应用程序。 2. **安装与配置**：如何在各种操作系统上安装Xen hypervisor，如Linux发行版，以及设置网络和存储配置，确保多虚拟机间的通信和数据安全。 3. **虚拟机管理**：创建、启动、停止和迁移虚拟机（VM）的方法，以及如何调整资源分配，如CPU和内存，以优化性能。 4. **安全性**：讨论Xen的安全特性，如隔离机制，以及如何防止一个虚拟机影响到其他虚拟机或主机系统的策略。 5. **高可用性与故障恢复**：介绍如何构建高可用性集群，以及在出现故障时如何恢复服务，保持业务连续性。 6. **性能监控与优化**：如何监控Xen环境的性能，识别瓶颈，并应用最佳实践进行优化。 7. **网络虚拟化**：阐述Xen如何处理虚拟机的网络连接，包括桥接、NAT和VLAN等网络模型。 8. **存储虚拟化**：讨论不同的存储解决方案，如块设备驱动、网络存储（iSCSI、NFS）以及存储区域网络（SAN）集成。 9. **动态资源调度**：讲解Xen的动态资源调度算法，如何根据需求自动调整虚拟机的资源。 10. **应用案例**：可能包含使用Xen在云环境、数据中心和企业中的实际应用案例，展示其在不同场景下的优势。 11. **技术审查与更新**：技术审阅者Rami Rosen可能会提供了对Xen最新版本的见解，确保信息的时效性和准确性。这本《The Book of Xen》通过深入的理论知识和实践经验，帮助读者掌握Xen虚拟化技术，无论你是初学者还是有经验的系统管理员，都能从中获益。通过学习，你将能够有效地管理和维护Xen环境，实现高效、安全的虚拟化基础设施。

xiv Contents in Detail

TROUBLESHOOTING 219

Troubleshooting Phase 1: Error Messages ............................................................... 220

Errors at Dom0 Boot ................................................................................ 220

DomU Preboot Errors ............................................................................... 222

Creating Domains in Low-Memory Conditions ............................................. 222

Configuring Devices in the DomU .............................................................. 223

Troubleshooting Disks .............................................................................. 223

VM Restarting Too Fast ............................................................................ 224

Troubleshooting Xen’s Networking ......................................................................... 225

The DomU Interface Number Increments with Every Reboot .......................... 227

iptables .................................................................................................. 227

Memory Issues ..................................................................................................... 228

Other Messages ................................................................................................... 228

A Constant Stream of 4GiB seg fixup Messages .......................................... 230

The Importance of Disk Drivers (initrd Problems) .......................................... 230

XenStore ................................................................................................ 231

Xen’s Logs ........................................................................................................... 232

dmesg and xm dmesg .............................................................................. 232

Logs and What Xen Writes to Them ........................................................... 232

Applying the Debugger ......................................................................................... 234

Xen’s Backend Architecture: Making Sense of the Debug Information ............ 234

Domain Stays in Blocked State .................................................................. 235

Debugging Hotplug ................................................................................. 236

strace .................................................................................................... 237

Python Path Issues ................................................................................................ 238

Mysterious Lockups .................................................................................. 238

Kernel Parameters: A Safe Mode .............................................................. 239

Getting Help ........................................................................................................ 239

Mailing Lists ........................................................................................... 239

The Xen Wiki .......................................................................................... 240

The Xen IRC Channel ............................................................................... 240

Bugzilla ................................................................................................. 240

Your Distro Vendor .................................................................................. 240

xen-bugtool ............................................................................................ 240

Some Last Words of Encouragement ....................................................................... 241

XM REFERENCE 243

xm’s Syntax ......................................................................................................... 244

xm Subcommands ................................................................................................ 244

THE STRUCTURE OF THE XEN CONFIG FILE 251

List of Directives ................................................................................................... 253

HVM Directives ....................................................................................... 258

Device Model Options ............................................................................. 260

INDEX 263

xvi Foreword

Whenever I do need separation of privilege on the same physical servers,

I’ve been able to get away with FreeBSD jails or User Mode Linux. I also do

a fair amount of real-time work, in which I need my code to be close to the

hardware for design—and sometimes performance—reasons.

For professional work, my company uses a mixture of proprietary

(VMware) and open source (Xen) virtualization and the results are out-

standing. Whether it’s to save money on hardware, save money on sysadmin

time, or enable new kinds of computing, virtualization is a winner and it’s

here to stay. I’ve seen Amazon and Google build gigantic clouds of virtualized

servers for their own use and for rental to customers, and this method has

driven down IT costs for both new and established companies of all sizes. It

probably saves power and lowers the industry’s carbon footprint as well.

I’m struggling to find a way to communicate how amazingly cool this is.

We try to write programs that fit into a single process, but they end up taking

a whole Unix system because of all the processes and databases and shell

scripts and file systems and UIDs they slop over. So we end up dedicating

physical servers to applications that have no performance- or security-related

reason to be on dedicated servers; but each one takes up some rack space

and some sysadmin time, and each one generates some minimum amount of

heat, and so on. Then along comes virtualization, and we’re back to adding

physical servers only when we’ve got a good reason to do so, which usually

means for capacity reasons.

Note that while I admire cloud computing, I also fear it. Amazon and

Google have their own virtualization APIs, and anyone who builds “version 1”

of a system to live inside one of these commercial clouds is probably signing

up to put “version 2” into the same cloud. Competition requires differentia-

tion and most vendors want to be different in capability, not just in cost

efficiency. In other words, lock-in is great for sellers but not so great for

buyers. Thus my attraction to enterprise virtualization—and specifically to

open source enterprise virtualization, with the resulting vertically open

ecosystem. I’ll build my own clouds whenever I need them—and with Xen,

so can you.

A word about Luke. He was a kid who lived down the street from my

sister, and she asked me to give him a chance. So I hired him at an anti-spam

company called MAPS (yes, that’s spam spelled backwards, pretty neat,

huh?), and he turned out to be a dumbass kid, like we all were at that age.

In the time since then, he has distinguished himself as a virtualizer and now,

with this book, as a writer. Xen is cool stuff, but it’s also deep and wide and

dense—that is to say, it’s a hard topic. Luke and Chris have unscrambled Xen

into the linear form of a printed book in about the best way I can imagine

anybody doing it, and I learned quite a bit about Xen from reading my

advance copy. The book is also fun to read without the fun being distracting

or dilutive.

Go forth and virtualize!

Paul Vixie

La Honda, California

September 2009

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