18

我正在考虑为 Google App Engine 开发一个应用程序,它应该不会获得太多流量。我真的宁愿不支付超过免费配额的费用。但是,通过使应用程序过载并超出配额似乎很容易引起拒绝服务攻击。是否有任何方法可以防止或使其更难超过免费配额?例如,我知道我可以限制来自 IP 的请求数量(使其更难超过 CPU 配额),但有没有办法让超过请求或带宽配额更难?

4

5 回答 5

16

没有内置工具可以防止 DoS。如果您使用 java 编写 Google Apps,那么您可以使用service.FloodFilter过滤器。以下代码将在您的任何 Servlet 执行之前执行。

package service;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;


/**
 * 
 * This filter can protect web server from simple DoS attacks
 * via request flooding.
 * 
 * It can limit a number of simultaneously processing requests
 * from one ip and requests to one page.
 *
 * To use filter add this lines to your web.xml file in a <web-app> section.
 * 
    <filter>
        <filter-name>FloodFilter</filter-name>
        <filter-class>service.FloodFilter</filter-class>
        <init-param>
            <param-name>maxPageRequests</param-name>
            <param-value>50</param-value>
        </init-param>
        <init-param>
            <param-name>maxClientRequests</param-name>
            <param-value>5</param-value>
        </init-param>
        <init-param>
            <param-name>busyPage</param-name>
            <param-value>/busy.html</param-value>
        </init-param>
    </filter>

    <filter-mapping>
        <filter-name>JSP flood filter</filter-name>
        <url-pattern>*.jsp</url-pattern>
    </filter-mapping>
 *  
 *  PARAMETERS
 *  
 *  maxPageRequests:    limits simultaneous requests to every page
 *  maxClientRequests:  limits simultaneous requests from one client (ip)
 *  busyPage:           busy page to send to client if the limit is exceeded
 *                      this page MUST NOT be intercepted by this filter
 *  
 */
public class FloodFilter implements Filter
{
    private Map <String, Integer> pageRequests;
    private Map <String, Integer> clientRequests;

    private ServletContext context;
    private int maxPageRequests = 50;
    private int maxClientRequests = 10;
    private String busyPage = "/busy.html";


    public void doFilter( ServletRequest request, ServletResponse response, FilterChain chain ) throws IOException, ServletException
    {
        String page = null;
        String ip = null;

        try {
            if ( request instanceof HttpServletRequest ) {
                // obtaining client ip and page URI without parameters & jsessionid
                HttpServletRequest req = (HttpServletRequest) request;
                page = req.getRequestURI();

                if ( page.indexOf( ';' ) >= 0 )
                    page = page.substring( 0, page.indexOf( ';' ) );

                ip = req.getRemoteAddr();

                // trying & registering request
                if ( !tryRequest( page, ip ) ) {
                    // too many requests in process (from one client or for this page) 
                    context.log( "Flood denied from "+ip+" on page "+page );
                    page = null;
                    // forwarding to busy page
                    context.getRequestDispatcher( busyPage ).forward( request, response );
                    return;
                }
            }

            // requesting next filter or servlet
            chain.doFilter( request, response );
        } finally {
            if ( page != null )
                // unregistering the request
                releaseRequest( page, ip );
        }
    }


    private synchronized boolean tryRequest( String page, String ip )
    {
        // checking page requests
        Integer pNum = pageRequests.get( page );

        if ( pNum == null )
            pNum = 1;
        else {
            if ( pNum > maxPageRequests )
                return false;

            pNum = pNum + 1;
        }

        // checking client requests
        Integer cNum = clientRequests.get( ip );

        if ( cNum == null )
            cNum = 1;
        else {
            if ( cNum > maxClientRequests )
                return false;

            cNum = cNum + 1;
        }

        pageRequests.put( page, pNum );
        clientRequests.put( ip, cNum );

        return true;
    }


    private synchronized void releaseRequest( String page, String ip )
    {
        // removing page request
        Integer pNum = pageRequests.get( page );

        if ( pNum == null ) return;

        if ( pNum <= 1 )
            pageRequests.remove( page );
        else
            pageRequests.put( page, pNum-1 );

        // removing client request
        Integer cNum = clientRequests.get( ip );

        if ( cNum == null ) return;

        if ( cNum <= 1 )
            clientRequests.remove( ip );
        else
            clientRequests.put( ip, cNum-1 );
    }


    public synchronized void init( FilterConfig config ) throws ServletException
    {
        // configuring filter
        this.context = config.getServletContext();
        pageRequests = new HashMap <String,Integer> ();
        clientRequests = new HashMap <String,Integer> ();
        String s = config.getInitParameter( "maxPageRequests" );

        if ( s != null ) 
            maxPageRequests = Integer.parseInt( s );

        s = config.getInitParameter( "maxClientRequests" );

        if ( s != null ) 
            maxClientRequests = Integer.parseInt( s );

        s = config.getInitParameter( "busyPage" );

        if ( s != null ) 
            busyPage = s;
    }


    public synchronized void destroy()
    {
        pageRequests.clear();
        clientRequests.clear();
    }
}

如果您使用的是 python,那么您可能必须滚动自己的过滤器。

于 2009-05-04T21:55:35.197 回答
7

我不确定这是否可能,但App Engine 常见问题解答表明,如果您可以证明这是 DOS 攻击,那么他们将退还与该攻击相关的任何费用。

于 2009-05-04T21:54:26.340 回答
2

似乎他们现在有一个可用于 Python 和 Java 的基于 IP 地址的过滤器(我知道这是一个旧线程,但它在 Google 搜索中仍然很高)。

https://developers.google.com/appengine/docs/python/config/dos

于 2012-05-15T02:27:22.350 回答
1

始终可以在 App Engine 应用程序前使用提供拒绝服务保护功能的服务。例如,Cloudflare 提供了备受推崇的服务https://www.cloudflare.com/waf/,还有其他的。我的理解(免责声明:我没有亲自使用过该服务)这些功能在免费计划中可用。

在应用程序本身中构建基于内存缓存的速率限制实现也相当容易。这是我从谷歌搜索此方法中获得的第一个结果:http: //blog.simonwillison.net/post/57956846132/ratelimitcache。这种机制是合理的,并且具有成本效益,因为共享的 memcache 使用可能就足够了并且是免费的。此外,走这条路线可以让您控制旋钮。缺点是应用程序本身必须处理 HTTP 请求并决定允许或拒绝它,因此可能需要处理成本(或 [免费] 配额耗尽)。

完全披露:我在 Google 的 App Engine 工作,与 Cloudflare 或 Simon Willison 没有任何关系。

于 2016-07-28T18:21:41.510 回答
1

GAE 防火墙最近发布,旨在取代以前相当有限的DoS 保护服务

它支持通过(REST)管理 API 以编程方式更新防火墙规则:apps.firewall.ingressRules可以与其他答案中描述的用于 DoS 检测的应用内逻辑相结合。不同之处在于,一旦部署了规则,违规请求将不再产生费用,因为它们不再到达应用程序,因此不需要应用程序内过滤本身。

于 2017-08-26T03:39:56.817 回答