配置 Haproxy 防止 DDOS ***
作为 load balancer, Happroxy 常常作为服务器的前端，向外界用户提供服务的入口，如果能在入口处处理安全相关问题，将极大简化后端的设计。事实上，Haproxy 不仅仅是一款开源出色的 load balancer（四层和七层），而且在安全上也相当出色。它配合内核 IP/TCP 协议栈，能够较好的抵抗 DOS, DDOS ***，还能通过限制单个 IP 的连接数和请求速率等，防止用户的恶意行为。Haproxy配置参数多的一塌糊涂，因而功能丰富，灵活多样，本文抛砖引玉，更多的安全功能请详见官网手册。
TCP syn flood attacks
通过向服务器发送大量的 TCP syn 分组，恶意用户实现了了 TCP syn flood ***，幸运的是，简单的配置内核网络参数即可防止这种***。
/etc/sysctl.conf
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[*] # Protection SYN flood
[*] net.ipv4.tcp_syncookies = 1
[*] net.ipv4.conf.all.rp_filter = 1
[*] net.ipv4.tcp_max_syn_backlog = 1024
[*] sysctl -p
Slowloris like attacks
一个 Http 请求通常包括头部、url、methods 等，服务器需要接收整个 Http 请求后会做出响应。恶意用户发送缓慢的 Http 请求，比如一个字节一个字节的发送头部，服务器将一直处于 wating 状态，从而耗费服务器的资源。Haproxy 通过配置 timeout http-request 参数，当一个用户的请求时间超过设定值时，Haproxy 断开与该用户的连接。
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[*] defaults
[*] option http-server-close
[*] mode http
[*] timeout http-request 5s# 防止 Slowloris like attacks
[*] timeout connect 5s
[*] timeout server 10s
[*] timeout client 30s
[*]
[*] listen stats
[*] bind 0.0.0.0:8880
[*] stats enable
[*] stats hide-version
[*] stats uri /
[*] stats realm HAProxy\ Statistics
[*] stats auth admin:admin
[*]
[*] frontend ft_web
[*] bind 0.0.0.0:8080
[*] default_backend bk_web
[*]
[*] backend bk_web
[*] balance roundrobin
[*] cookie MYSRV insert indirect nocache
[*] server srv1 192.168.1.2:80 check cookie srv1 maxconn 100
[*] server srv2 192.168.1.3:80 check cookie srv2 maxconn 100
通过 telnet 登录验证结果
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[*] telnet 127.0.0.1 8080
[*] Trying 127.0.0.1...
[*] Connected to 127.0.0.1.
[*] Escape character is '^]'.
[*] HTTP/1.0 408 Request Time-out
[*] Cache-Control: no-cache
[*] Connection: close
[*] Content-Type: text/html
[*] 408 Request Time-out
[*] Your browser didn't send a complete request in time.
[*] Connection closed by foreign host.
Limiting the number of connections per users
以网站为例，普通用户访问网站，或者从网站下载东西时，浏览器一般会建立 5-7 个 TCP 链接。当一个恶意打开了大量 TCP 链接时，耗费服务器大量资源，影响其它用户的访问，因此我们需要根据实际情况，限制同一个用户的链接数。
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[*] defaults
[*] option http-server-close
[*] mode http
[*] timeout http-request 5s
[*] timeout connect 5s
[*] timeout server 10s
[*] timeout client 30s
[*]
[*] listen stats
[*] bind 0.0.0.0:8880
[*] stats enable
[*] stats hide-version
[*] stats uri /
[*] stats realm HAProxy\ Statistics
[*] stats auth admin:admin
[*]
[*] frontend ft_web
[*] bind 0.0.0.0:8080
[*]
[*] # Table definition
[*] stick-table type ip size 100k expire 30s store conn_cur
[*]
[*] # Allow clean known IPs to bypass the filter
[*] tcp-request connection accept if { src -f /etc/haproxy/whitelist.lst }
[*] # Shut the new connection as long as the client has already 10 opened
[*] tcp-request connection reject if { src_conn_cur ge 10 }
[*] tcp-request connection track-sc1 src
[*]
[*] default_backend bk_web
[*]
[*] backend bk_web
[*] balance roundrobin
[*] cookie MYSRV insert indirect nocache
[*] server srv1 192.168.1.2:80 check cookie srv1 maxconn 100
[*] server srv2 192.168.1.3:80 check cookie srv2 maxconn 100
注：若某些用户在同一个私有网段通过 NAT 访问网站，这样的配置存在不合理之处，最好把 NAT 处的公网地址添加到 whitelist.lst 文件中。
利用 apache 测试工具做验证，和服务器一直保持建立 10 个链接。
ab -n 50000000 -c 10 http://127.0.0.1:8080/用 telnet 打开第 11 个链接，服务器拒绝该链接。 view plain copy telnet 127.0.0.1 8080Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.Connection closed by foreign host.
Limiting the connection rate per user
仅仅限制单个用户的并发链接数并意味着万事大吉，如果用户在短时间内向服务器不断的发送建立和关闭链接请求，也会耗费服务器资源，影响服务器端的性能，因此需要控制单个用户的访问速率。
通常情况下，考虑到用户通过浏览器一般会建立 5-7 条 TCP 链接，我们可以认为普通用户在 3 秒内不应该建立超过 20 条链接。
view plain copy defaults option http-server-close mode http timeout http-request 5s timeout connect 5s timeout server 10s timeout client 30s listen stats bind 0.0.0.0:8880 stats enable stats hide-version stats uri / stats realm HAProxy\ Statistics stats auth admin:admin frontend ft_web bind 0.0.0.0:8080 # Table definition stick-table type ip size 100k expire 30s store conn_cur,conn_rate(3s) # Allow clean known IPs to bypass the filter tcp-request connection accept if { src -f /etc/haproxy/whitelist.lst } # Shut the new connection as long as the client has already 10 opened or rate more than 20 tcp-request connection reject if { src_conn_cur ge 10 } || { src_conn_rate ge 20} tcp-request connection track-sc1 src default_backend bk_web backend bk_web balance roundrobin cookie MYSRV insert indirect nocache server srv1 192.168.1.2:80 check cookie srv1 maxconn 100 server srv2 192.168.1.3:80 check cookie srv2 maxconn 100注：若某些用户在同一个私有网段通过 NAT 访问网站，这样的配置存在不合理之处，最好把 NAT 处的公网地址添加到 whitelist.lst 文件中。测试，采用 ab 打开 20 个链接。(本次测试把 限制单个用户并发数功能 去掉)ab -n 20 -c 1 -r http://127.0.0.1:8080/再用 telnet 打开第 21 个链接，服务器拒绝该请求。 view plain copy telnet 127.0.0.1 8080Trying 127.0.0.1...Connected to 127.0.0.1.Escape character is '^]'.Connection closed by foreign host.
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