云计算应用架构：设计与实践指南

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"云计算应用架构" 由 George Reese 所著，旨在为各种职业阶段的技术人员提供指导，包括需要为云编写代码的开发者、需要设计云系统架构的架构师以及负责迁移到云端的IT经理。这本书虽不包含大量代码，但会提供作者在Java和Python编程，以及与MySQL、偶尔的SQL Server或Oracle数据库交互时的最佳实践。如果你设计、构建或维护可能会部署到云端的Web应用程序，这本书将对你有所帮助。云计算是信息技术领域的一个关键概念，它涉及通过互联网提供计算资源和服务，如服务器、存储、数据库、网络、软件等，而不是本地设备上。云应用架构是指在云环境中设计和构建应用程序的结构，它需要考虑可扩展性、高可用性、灵活性和成本效益。本书探讨了如何适应云环境的设计原则，这些原则不仅适用于特定的编程语言，而是通用的最佳实践。作者强调跨语言的适用性，这意味着开发者可以从书中学习到如何为任何编程语言构建云原生应用。书中的内容可能涵盖以下几个方面： 1. **云服务模型**：介绍公有云、私有云和混合云的概念，以及它们各自的优势和适用场景。 2. **微服务架构**：讲解如何将大型应用分解为小型、独立的服务，以便于部署、扩展和维护。 3. **容器化和编排**：讨论Docker等容器技术如何封装应用及其依赖，以及Kubernetes等编排工具如何管理这些容器。 4. **负载均衡和伸缩**：介绍如何通过自动化手段实现对应用流量的分配和资源的动态扩展。 5. **数据存储策略**：分析在云中选择合适的数据库服务，如关系型数据库（MySQL）、非关系型数据库（NoSQL）以及数据湖解决方案。 6. **安全性与合规**：探讨云环境下的数据保护、访问控制、网络安全和合规问题。 7. **持续集成/持续部署(CI/CD)**：展示如何建立高效的自动化测试和部署流程。 8. **监控和日志管理**：讲解如何收集和分析应用运行时的性能数据，以优化和故障排查。 9. **成本优化**：提供在云中运行应用的经济策略，包括资源利用率和预付费与按需付费模式的权衡。通过阅读此书，读者可以掌握设计云应用架构的关键技能，从而更好地应对云计算环境带来的挑战，并实现高效、可靠的云端服务。

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.

C LO UD C OM PU TI NG 5

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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