使用Node.js入门亚马逊云服务

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"Beginning Amazon Web Services with Node.js" 是一本面向初学者的指南，教导如何在AWS上配置、部署和维护可扩展的Node.js应用程序，无论是小型还是大型项目。本书着重于解决通过PaaS（平台即服务）托管Node.js应用时可能遇到的问题，通过直接在AWS上部署来消除中间环节。在书中，读者将从一个基于Express.js的简单RESTful Web服务开始，该服务已经预建并可以在本地环境中运行。作者会介绍AWS中最强大的工具，并讲解如何配置项目以利用这些工具。通过AWS JavaScript SDK的代码示例和AWS控制台的教程，读者将学会如何实现安全的用户身份验证、服务器自动扩展、负载均衡器、CDN、自定义缓存行为以及故障监控。 Node.js的单线程设计和高输入/高输出的应用特性使其非常适合云环境。如果主要任务是处理大量HTTP或Web请求，它可以根据分配的计算能力很好地扩展。AWS提供了一系列服务，帮助企业更快地行动，降低成本，并扩展应用程序。无论大型企业还是初创公司，都信任AWS来支持各种工作负载。通过正确利用AWS，开发者可以构建一个Node.js应用，当流量大时自动扩展以处理大规模的访问量，然后在用户需求降低时自动缩减到较低的配置。本书将涵盖以下内容： - 使用AWS OpsWorks架构和配置为云托管设计的安全Web应用。 - 将AWS CloudWatch、SES等AWS服务集成到代码中。 - 使用AWS Route 53配置域名以利用负载均衡器、CDN和其他性能增强服务。 - 使用AWS OpsWorks部署应用，并利用AWS服务进行监控、扩展和维护。 - 学习如何利用AWS服务自动调整Node.js应用的规模，以应对流量变化。目标读者是初阶Node.js开发者，通常依赖Heroku或Parse等PaaS服务来托管Web应用。本书旨在让读者能够直接在AWS上工作，管理自己的基础设施。AWS提供的服务允许开发者构建能够在需求高峰时自动扩展、低峰时自动收缩的Node.js应用。书中的章节包括： 1. 开始使用Amazon Web Services 2. 使用AWS OpsWorks 3. OpsWorks第二部分：数据库和扩展 4. CloudFront和DNS管理 5. 简单存储服务和内容分发 6. 简单电子邮件服务 7. 监控应用程序 8. 应用程序安全通过阅读本书，读者将获得在AWS上构建和管理高效Node.js应用所需的知识和技能。

CHAPTER 1 ■ GETTING STARTED WITH AMAZON WEB SERVICES

Note ■ Full documentation for the mysql module is available at https://github.com/felixge/node-mysql.

As mentioned previously, globals is an object that stores common variables without polluting the

global namespace and is used here for convenience. The MySQL database connection is initialized as

connection, using the database configuration stored in globals. Let’s look at the first method, which we

already know about, getAllUsers().

function getAllUsers(callback){

connection.query('SELECT username, userID FROM users', function(err, rows, fields){

if(err){

callback(err);

} else {

callback(null, rows);

}

});

}

This method is about as simple as a model-getter function can get. There are no parameters to validate,

no user input to escape, nor any other intermediary functions. We simply retrieve all users from the database

and return them to the callback function in routes/user. For a moment, let’s scroll to the very bottom of the

file and note exports assignments.

exports.getAllUsers = getAllUsers;

exports.getUser = getUser;

exports.createUser = createUser;

exports.loginUser = loginUser;

exports.logoutUser = logoutUser;

These lines are very important, as they are the means by which you make a method in this file public;

otherwise, all methods are private or inaccessible to other objects. If you build additional functionality with

this sample application, it’s easy to forget this step.

Review—The Order of Things

Returning to /routes/user for a moment, you should see now how a request is handled. Here’s a quick

recap of how a client would retrieve a list of users from our app:

1. server.js is listening for all HTTP requests at the designated port.

2. The client makes an HTTP GET request to /users/.

3. Server.js forwards the request to the controller at /routes/users.

4. The controller at /routes/users notes that the request is for “/” relative to “/

users” and passes the request to the corresponding listener method.

5. The GET “/” listener in the controller calls model.getAllUsers().

CHAPTER 1 ■ GETTING STARTED WITH AMAZON WEB SERVICES

6. The model method getAllUsers() queries the database, processes the results,

and returns the data set to the controller.

7. The controller populates the response object with data.

8. server.js sends an HTTP response with the data requested by the user.

Does that all make sense? If you’re already familiar with ExpressJS, it probably didn’t tell you anything

new. If you’re learning about this for the first time, don’t worry; we will be spending a lot of time with these

concepts in further lessons. And the best way to learn is to try writing your own routes and seeing what it

takes to make them function. Never underestimate the power of trial and error!

Example—Working with Parameters

Let’s return to /routes/users to look at another concept. So far, we’ve looked at handling a basic request

without any parameters or client input. When you have no variables involved, there is a very small likelihood

of failure. Once we start accepting specific requests from the client, the points of failure start to add up

quickly. We can look at the /users/login route as an example.

/* POST user login. */

router.post('/login', function(req, res) {

if(req.param('username') && req.param('password') ){

var params = {

username: req.param('username').toLowerCase(),

password: req.param('password')

};

model.loginUser(params, function(err, obj){

if(err){

res.status(400).send({error: 'Invalid login'});

} else {

res.send(obj);

}

});

} else {

res.status(400).send({error: 'Invalid login'});

}

});

This route accepts HTTP POST requests and expects that the client has sent both a username and

password. However, we cannot assume that both parameters were included. As such, we have to check that

the parameters exist before we try to use them. If the parameters have been included, we proceed. If not, an

invalid login error is sent in response to the request.

We can use the controller both to validate input and to format parameters to pass to the model.

In this case, before we send the user’s login credentials to the model, we also want to enforce one rule:

usernames should be case insensitive. The params object is instantiated with the request parameters, and

the username is converted to lowercase when params.username is set. We can then look at the model, to

see what happens next.

CHAPTER 1 ■ GETTING STARTED WITH AMAZON WEB SERVICES

function loginUser(params, callback){

connection.query('SELECT username, password, userID FROM users WHERE username=' +

connection.escape(params.username), function(err, rows, fields) {

if(err){

callback(err);

} else if(rows.length > 0){

var response = {

username: rows[0].username,

userID: rows[0].userID

}

callback(null, response);

} else {

var error = new Error("Invalid login");

callback(error);

}

});

}

For now, we’re selecting the user from the database, if the username is valid. In the future, we will be

decrypting the user’s password to authenticate the user. Currently, we are automatically returning a success

response, which includes the username and user ID of the authenticated user. The important lesson here

is that the controller is used to sanitize and validate client input before sending it to the model. It is a good

idea to separate concerns and encapsulate functionality in this way. The model will expect an object with

the necessary properties to be sent to its methods, and the controller is responsible for constructing that

object or rejecting malformed requests. If you follow this pattern, you will be able to safely reuse the public

methods in your model classes in different scenarios, and your app will be much easier to maintain and

debug in the long run.

Try It Out

It’s time to fire up the app and see it in action. If the app isn’t running, open your command-line interface,

navigate to the app directory, and type node server.js. Open your REST client, and enter the following

URL:

http://localhost:8081/users/register

If you’re running the app on a different port, remember to replace 8081. Set your HTTP method to POST.

Add POST parameters named username, password, and email. You can enter whatever values you want into

those parameters. Send the request!

You should receive the following success message:

{

"message": "Registration successful!"

}

Next, you should be able to log in with the username you just registered. Remove the email parameter

and change the URL to

http://localhost:8081/users/login

CHAPTER 1 ■ GETTING STARTED WITH AMAZON WEB SERVICES

You should receive the following username and user ID in response:

{

"username": "adam",

"userID": 1

}

You can now make a GET request in the browser to http://localhost:8081/users/. You should see the

user you created in the response. You can create additional users, and they will appear in this response as

well. From here, you can use the user ID from the login response to create albums and photos for your user. I

will discuss these in more detail soon. For now, let’s make a quick GET request to the user detail API endpoint

at /users/user/:user, replacing :user with the username you just registered. You should see something

similar to the following response:

{

"username":"adam",

"userID":1,

"albums":[]

}

For now, there’s not much new information here. But once you start creating albums for this user, you

will get information about them here. Let’s take a look at albums next.

Albums

Each user can have an unlimited number of albums. The album object is very simple, consisting of a title

and user ID. Any number of photos can also be associated with the album.

Albums have the following functionality:

Create a new album (• POST /albums/upload)

params: • userID, title

Gets an album by ID, including all photos included in it (• GET /albums/id/:albumID)

params: • albumID

Delete an album (• POST /albums/delete)

params: • albumID

Let’s open /routes/albums.js and take a closer look. The variables declared at the top should already

be familiar. In this case, you can see that the model variable is set to /lib/model/model-albums.js. The

first route will allow us to create an album. Using the user ID you received when you registered, point your

RESTful client to http://localhost:8081/albums/upload, set the method to POST, and add fields for the

user ID and title. You can put whatever name you want in the title. We’ll go with “Hello World” for now. You

should receive the following response:

{

"id":7,

"title":"Hello World"

}

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