云计算应用架构：探索与实践

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“云计算应用架构”是一本由George Reese编著的书籍，主要探讨了云环境下的应用程序设计和架构。本书由O'Reilly Media, Inc.出版，并在全球多个城市发行。内容涵盖云应用架构的各个方面，旨在帮助读者理解和构建高效、可扩展的云基础设施。在云计算应用架构中，作者George Reese深入探讨了以下几个关键知识点： 1. **云计算基础**：书中首先介绍了云计算的基本概念，包括IaaS（基础设施即服务）、PaaS（平台即服务）和SaaS（软件即服务）三种主要的服务模式，以及公有云、私有云和混合云的区别。 2. **云架构设计原则**：讨论了云架构设计时应遵循的原则，如可伸缩性、弹性、高可用性、安全性、成本效益和可维护性等，这些都是构建云应用时需要考虑的关键因素。 3. **云中的数据管理**：详述了如何在云环境中管理数据，包括数据存储策略、备份与恢复、数据安全以及大数据处理技术，如Hadoop和NoSQL数据库。 4. **微服务架构**：随着云技术的发展，微服务架构成为一种流行的架构模式，书中会介绍其设计理念，如何拆分服务，以及如何实现服务间的通信和协调。 5. **容器技术**：Docker等容器技术在云应用中的应用，以及如何通过容器化提升应用部署的灵活性和一致性。 6. **DevOps实践**：讨论了DevOps文化在云环境中的重要性，包括自动化测试、持续集成/持续交付(CI/CD)流程，以及监控和日志管理。 7. **安全性与合规性**：分析了云环境下的安全挑战，包括数据保护、访问控制、网络安全和合规性要求，以及如何实施有效的安全策略。 8. **云迁移策略**：提供了从传统IT环境向云端迁移的策略和方法，包括评估、规划、迁移过程和后期的优化。 9. **性能优化与成本控制**：探讨如何在云环境中优化应用性能，同时控制成本，包括资源调度、负载均衡和计费模型分析。 10. **案例研究**：通过实际的云应用案例，展示了理论知识在实际项目中的应用，帮助读者更好地理解和学习云架构设计。此书对于IT专业人士、系统架构师和开发者来说是一份宝贵的资源，它不仅提供了理论知识，还提供了实用的指导，帮助读者适应和利用云计算的力量来构建和运维现代应用。

The Cloud

The cloud is not simply the latest fashionable term for the Internet. Though the Internet is a

necessary

foundation for the cloud, the cloud is something more than the Internet. The cloud

is where you go to use technology when you need it, for as long as you need it, and not a

minute more. You do not install anything on your desktop, and you do not pay for the

technology when you are not using it.

The cloud can be both software and infrastructure. It can be an application you access through

the Web or a server that you provision exactly when you need it. Whether a service is software

or hardware, the following is a simple test to determine whether that service is a cloud service:

If you can walk into any library or Internet cafe and sit down at any computer without preference

for operating system or browser and access a service, that service is cloud-based.

I have defined three criteria I use in discussions on whether a particular service is a cloud

service:

• The service is accessible via a web browser (nonproprietary) or web services API.

• Zero capital expenditure is necessary to get started.

• You pay only for what you use as you use it.

I don’t expect those three criteria to end the discussion, but they provide a solid basis for

discussion and reflect how I view cloud services in this book.

If you don’t like my boiled-down cloud computing definition, James Governor has an excellent

blog entry on “15 Ways to Tell It’s Not Cloud Computing,” at

http://www.redmonk.com/

jgovernor/2008/03/13/15-ways-to-tell-its-not-cloud-computing

Software

As I mentioned earlier, cloud services break down into software services and infrastructure

services. In terms of maturity, software in the cloud is much more evolved than hardware in

the cloud.

Software as a Service

(SaaS) is basically a term that refers to software in the cloud. Although

not all SaaS systems are cloud systems, most of them are.

SaaS is a web-based software deployment model that makes the software available entirely

through a web browser. As a user of SaaS software, you don’t care where the software is hosted,

what kind of operating system it uses, or whether it is written in PHP, Java, or .NET. And,

above all else, you don’t have to install a single piece of software anywhere.

Gmail, for example, is nothing more than an email program you use in a browser. It provides

the same functionality as Apple Mail or Outlook, but without the fat client. Even if your domain

does not receive email through Gmail, you can still use Gmail to access your mail.

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SalesForce.com is another variant on SaaS. SalesForce.com is an enterprise customer

relationship

management (CRM) system that enables sales people to track their prospects and

leads, see where those individuals sit in the organization’s sales process, and manage the

workflow of sales from first contact through completion of a sale and beyond. As with Gmail,

you don’t need any software to access SalesForce.com: point your web browser to the

SalesForce.com website, sign up for an account, and get started.

SaaS systems have a few defining characteristics:

Availability via a web browser

SaaS software never requires the installation of software on your laptop or desktop. You

access it through a web browser using open standards or a ubiquitous browser plug-in.

Cloud computing and proprietary desktop software simply don’t mix.

On-demand availability

You should not have to go through a sales process to gain access to SaaS-based software.

Once you have access, you should be able to go back into the software any time, from

anywhere.

Payment terms based on usage

SaaS does not need any infrastructure investment or fancy setup, so you should not have

to pay any massive setup fees. You should simply pay for the parts of the service you use

as you use them. When you no longer need those services, you simply stop paying.

Minimal IT demands

If you don’t have any servers to buy or any network to build out, why do you need an IT

infrastructure? While SaaS systems may require some minimal technical knowledge for

their configuration (such as DNS management for Google Apps), this knowledge lays

within the realm of the power user and not the seasoned IT administrator.

One feature of some SaaS deployments that I have intentionally omitted is multitenancy. A

number of SaaS vendors boast about their multitenancy capabilities—some even imply that

multitenancy is a requirement of any SaaS system.

A multitenant application is server-based software that supports the deployment of multiple

clients in a single software instance. This capability has obvious advantages for the SaaS vendor

that, in some form, trickle down to the end user:

• Support for more clients on fewer hardware components

• Quicker and simpler rollouts of application updates and security patches

• Architecture that is generally more sound

The ultimate benefit to the end user comes indirectly in the form of lower service fees, quicker

access to new functionality, and (sometimes) quicker protection against security holes.

However, because a core principle of cloud computing is a lack of concern for the underlying

architecture of the applications you are using, the importance of multitenancy is diminished

when looking at things from that perspective.

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As we discuss in the next section, virtualization technologies essentially render the

architectural advantages of multitenancy moot.

Hardware

general, hardware in the cloud is conceptually harder for people to accept than software in

the cloud. Hardware is something you can touch: you own it; you don’t license it. If your server

catches on fire, that disaster matters to you. It’s hard for many people to imagine giving up the

ability to touch and own their hardware.

With hardware in the cloud, you request a new “server” when you need it. It is ready as quickly

as 10 minutes after your request. When you are done with it, you release it and it disappears

back into the cloud. You have no idea what physical server your cloud-based server is running,

and you probably don’t even know its specific geographic location.

THE BARRIER OF OLD EXPECTATIONS

The hardest part for me as a vendor of cloud-based computing services is answering the question,

“Where are our servers?” The real answer is, inevitably, “I don’t know—somewhere on the East

Coast of the U.S. or Western Europe,” which makes some customers very uncomfortable. This lack

of knowledge of your servers’ location, however, provides an interesting physical security benefit,

as it becomes nearly impossible for a motivated attacker to use a physical attack vector to

compromise your systems.

The advantages of a cloud infrastructure

Think about all of the things you have to worry about when you own and operate your own

servers:

Running out of capacity?

Capacity planning is always important. When you own your own hardware, however,

you have two problems that the cloud simplifies for you: what happens when you are

wrong (either overoptimistic or pessimistic), and what happens if you don’t have the

expansion capital when the time comes to buy new hardware. When you manage your

own infrastructure, you have to cough up a lot of cash for every new Storage Area Network

(SAN) or every new server you buy. You also have a significant lead time from the moment

you decide to make a purchase to getting it through the procurement process, to taking

delivery, and finally to having the system racked, installed, and tested.

What happens when there is a problem?

Sure, any good server has redundancies in place to survive typical hardware problems.

Even if you have an extra hard drive on hand when one of the drives in your RAID array

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fails, someone has to remove the old drive from the server, manage the RMA,

and put

the new drive into the server. That takes time and skill, and it all needs to happen in a

timely fashion to prevent a complete failure of the server.

What happens when there is a disaster?

If an entire server goes down, unless you are in a high-availability infrastructure, you have

a disaster on your hands and your team needs to rush to address the situation. Hopefully,

you have solid backups in place and a strong disaster recovery plan to get things

operational ASAP. This process is almost certainly manual.

Don’t need that server anymore?

Perhaps your capacity needs are not what they used to be, or perhaps the time has come

to decommission a fully depreciated server. What do you do with that old server? Even if

you give it away, someone has to take the time to do something with that server. And if

the server is not fully depreciated, you are incurring company expenses against a machine

that is not doing anything for your business.

What about real estate and electricity?

When you run your own infrastructure (or even if you have a rack at an ISP), you may

be paying for real estate and electricity that are largely unused. That’s a very ungreen

thing, and it is a huge waste of money.

None of these issues are concerns with a proper cloud infrastructure:

• You add capacity into a cloud infrastructure the minute you need it, and not a moment

sooner. You don’t have any capital expense associated with the allocation, so you don’t

have to worry about the timing of capacity needs with budget needs. Finally, you can be

up and running with new capacity in minutes, and thus look good even when you get

caught with your pants down.

• You don’t worry about any of the underlying hardware, ever. You may never even know

if the physical server you have been running on fails completely. And, with the right tools,

you can automatically recover from the most significant disasters while your team is

asleep.

• When you no longer need the same capacity or you need to move to a different virtual

hardware configuration, you simply deprovision your server. You do not need to dispose

of the asset or worry about its environmental impact.

• You don’t have to pay for a lot of real estate and electricity you never use. Because you

are using a fractional portion of a much beefier piece of hardware than you need, you are

maximizing the efficiency of the physical space required to support your computing needs.

Furthermore, you are not paying for an entire rack of servers with mostly idle CPU cycles

consuming electricity.

Return merchandise authorization. When you need to return a defective part, you generally have to go

through some vendor process for returning that part and obtaining a replacement.

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Hardware virtualization

Hardware virtualization is the enabling technology behind many of the cloud infrastructure

vendors offerings, including Amazon Web Services (AWS).

†

If you own a Mac and run

Windows or Linux inside Parallels or Fusion, you are using a similar virtualization technology

to those that support cloud computing. Through virtualization, an IT admin can partition a

single physical server into any number of virtual servers running their own operating systems

in their allocated memory, CPU, and disk footprints. Some virtualization technologies even

enable you to move one running instance of a virtual server from one physical server to

another. From the perspective of any user or application on the virtual server, no indication

exists to suggest the server is not a real, physical server.

A number of virtualization technologies on the market take different approaches to the

problem of virtualization. The Amazon solution is an extension of the popular open source

virtualization system called Xen. Xen provides a hypervisor layer on which one or more guest

operating systems operate. The hypervisor creates a hardware abstraction that enables the

operating systems to share the resources of the physical server without being able to directly

access those resources or their use by another guest operating system.

A common knock against virtualization—especially for those who have experienced it in

desktop software—is that virtualized systems take a significant performance penalty. This

attack on virtualization generally is not relevant in the cloud world for a few reasons:

• The degraded performance of your cloud vendor’s hardware is probably better than the

optimal performance of your commodity server.

• Enterprise virtualization technologies such as Xen and VMware use paravirtualization as

well as the hardware-assisted virtualization capabilities of a variety of CPU manufacturers

to achieve near-native performance.

Cloud storage

Abstracting your hardware in the cloud is not simply about replacing servers with

virtualization. It’s also about replacing your physical storage systems.

Cloud storage enables you to “throw” data into the cloud and without worrying about how it

is stored or backing it up. When you need it again, you simply reach into the cloud and grab

it. You don’t know how it is stored, where it is stored, or what has happened to all the pieces

of hardware between the time you put it in the cloud and the time you retrieved it.

As with the other elements of cloud computing, there are a number of approaches to cloud

storage on the market. In general, they involve breaking your data into small chunks and

storing that data across multiple servers with fancy checksums so that the data can be retrieved

†

Other approaches to cloud infrastructure exist, including physical hardware on-demand through

companies such as AppNexus and NewClouds. In addition, providers such as GoGrid (summarized in

Appendix B) offer hybrid solutions.

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