使用Erlang构建Web应用程序实战

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"使用Erlang开发web应用，书中范例所使用的webserver为Yaws" 在《Building Web Applications with Erlang》这本书中，作者Zachary Kessin深入介绍了如何利用Erlang这一编程语言来构建高效、可扩展的Web应用程序。Erlang是一种面向并发的、函数式编程语言，以其在分布式系统和高容错性方面的优势而闻名。Yaws则是一个由Erlang编写的高性能Web服务器，它支持动态内容生成，提供了对HTTP协议的完整实现，并且能够处理大量的并发连接。 Erlang的关键特性包括其轻量级进程模型、消息传递机制以及内置的错误恢复能力，这些特性使得Erlang在构建大型、高并发的网络应用时表现出色。在Web开发中，Erlang可以用来处理复杂的并发请求，提供高可用性和稳定性，同时保持较低的延迟。 Yaws作为一个Erlang Web服务器，其设计目标是快速响应和低内存占用。Yaws支持多种Web应用模型，包括静态文件服务、CGI脚本、ASPD（Yaws Specific Scripting Domain）和通过Erlang OTP接口直接调用Erlang代码。这种灵活性使得开发者可以选择最适合他们需求的部署方式。书中可能涵盖了以下主题： 1. Erlang基础：介绍Erlang的语法、数据类型、函数式编程概念以及Erlang的并发模型。 2. Yaws服务器详解：Yaws的架构、配置、启动和管理，以及如何通过Yaws部署Erlang应用。 3. Web应用开发：讲解如何使用Erlang编写HTTP服务器端的代码，处理HTTP请求和响应，以及动态内容生成。 4. 高并发处理：讨论Erlang进程模型在处理大量并发连接时的优势，以及如何优化性能。 5. 错误处理和容错性：介绍Erlang的错误处理机制和分布式系统的容错设计。 6. 模块化和测试：最佳实践，如模块划分、单元测试和集成测试在Erlang项目中的应用。 7. 部署和运维：如何将Erlang Web应用部署到生产环境，以及监控和维护的方法。通过阅读本书，读者不仅可以学习到Erlang编程语言，还能掌握如何利用Yaws构建健壮的Web服务，这对于希望在高并发、高可用性场景下构建Web应用的开发者来说，是一份宝贵的参考资料。

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xiv | Preface

One of the first major projects to use Erlang was the Ericsson AXD301 switch, which

used about a million lines of Erlang code along with some device drivers and other low-

level components that were written in C. The AXD301 switch has achieved an unpre-

cedented level of reliability in the field—in some cases, it has achieved “nine 9s” reli-

ability!

The amount of time that the system could be expected to be offline could be

measured in milliseconds per year. (This was for the entire network, not a single node.)

Clearly, most systems written in Erlang will not achieve that level of reliability. With

careful design and testing, it’s possible for a system to hit six 9s (about 30 seconds of

downtime per year). However, reaching that is beyond the scope of this book, and

requires a very careful study of risks that may cause the system to be unavailable and

ensuring that no single failure (in particular, beyond your code) could cause that. For

example, having three connections to the Internet with different ISPs is great, but if all

three go through the same conduit it only takes one guy with a backhoe to cut all three

wires and take a system offline.

Erlang applications can be upgraded in place. If an application is running on a cluster

of servers and a bug is discovered in one module, there is no need to stop the system

to upgrade to a new version of the software—Erlang provides a method to upgrade the

code as it runs so that customers never need to be interrupted. This is a major advantage

over a system where an application needs to be offline for an hour or more each time

a new version of the software is rolled out, costing real money as customers are not able

to use the system.

Erlang is also designed to support clusters of computers. In fact, to have a scalable and

fault-tolerant system, it must run on more than one computer. As any given computer

can fail, it is important that the system be able to deal with the case of a node in the

cluster going offline and still providing services to the customers. How many nodes a

system should run on is a complex issue, but it starts with the question “What is the

probability of all the remaining nodes failing before I can bring a new node online?”

If you Google “Erlang”, you will see references to “Erlang-B” and “Er-

lang-C”. These are measures of telephone capacity that are probably of

great importance if you are building a call center, but have nothing to

do with the programming language.

Erlang’s Advantages

Erlang does many things differently. In most programming languages, concurrency is

an afterthought. Each process in PHP, for example, runs independently and generally

communicates with other PHP processes only via external resources like a database or

memcached server. In Erlang, concurrency is built in from the very base of the system.

1. In practice, this often means “The system was more reliable than our way of measuring it.”

2 | Chapter 1: Building Scalable Systems with Erlang and REST

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使用Erlang构建Web应用程序实战

Building Web Applications with SVG

Building Web Applications with Erlang.2012.英文

Building Web Applications with Erlang

Building.Web.Applications.with.Erlang

building_web_applications_with_erlang:这是 Zachary Kessin (O'Reilly Media) 使用 Erlang 构建 Web 应用程序的示例代码库

Erlang-Formula.zip_Erlang B _Erlang-B_erlang_erlang B计算_erlang C

Erlang_B_model.rar_Erlang B _Erlang B model_Wireless Handbook_e

megaco_session-0.5.rar_erlang_erlang Megaco_megaco

ErlangB-and-ErlangC.zip_erlangB_erlangb图_erlangb表_爱尔兰C公式_爱尔兰公式

HW2.rar_erlang_erlang C

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