Centos7+Haproxy实现Apache负载均衡
说到Linux下的负载均衡，其实有很多服务是可以实现的，比如：haproxy，lvs，nginx，这些服务都可以做负载均衡，而我们今天主要介绍的是Haproxy实现Apache的负载均衡。一般做法是通过Haproxy+Keeplive实现高可用负载均衡的，我们将会在后面的文章介绍。
目的：访问Haproxy自动轮询分配后台服务器
环境介绍：
Hostname：A-S
IP:192.168.5.21
Role：Apache
Hostname：B-S
IP:192.168.5.22
Role：Apache
Hostname：C-S
IP:192.168.5.23
Role：Haproxy
我们先看看安装完默认的Haproxy的配置介绍：
vim /etc/haproxy/haproxy.cfg
#---------------------------------------------------------------------
# Example configuration for a possible web application. See the
# full configuration options online.
#
# http://haproxy.1wt.eu/download/1.4/doc/configuration.txt
#
#---------------------------------------------------------------------
#---------------------------------------------------------------------
# Global settings
#---------------------------------------------------------------------
global
# to have these messages end up in /var/log/haproxy.log you will
# need to:
#
# 1) configure syslog to accept network log events. This is done
# by adding the '-r' option to the SYSLOGD_OPTIONS in
# /etc/sysconfig/syslog
#
# 2) configure local2 events to go to the /var/log/haproxy.log
# file. A line like the following can be added to
# /etc/sysconfig/syslog
#
# local2.* /var/log/haproxy.log
#
log 127.0.0.1 local2 #日志输出配置，所有日志都记录在本机，通过local2输出
chroot /var/lib/haproxy #改变当前工作目录。
pidfile /var/run/haproxy.pid #所属运行的gid
maxconn 4000 #最大连接数
user haproxy
group haproxy
daemon #以后台形式运行haproxy
# turn on stats unix socket
stats socket /var/lib/haproxy/stats
#---------------------------------------------------------------------
# common defaults that all the 'listen' and 'backend' sections will
# use if not designated in their block
#---------------------------------------------------------------------
defaults
mode http #默认的模式mode { tcp|http|health }，tcp是4层，http是7层，health只会返回OK
log global
option httplog
option dontlognull
option http-server-close
option forwardfor except 127.0.0.0/8
option redispatch #当serverId对应的服务器挂掉后，强制定向到其他健康的服务器
retries 3 #两次连接失败就认为是服务器不可用
timeout http-request 10s
timeout queue 1m
timeout connect 10s #连接超时
timeout client 1m #客户端超时
timeout server 1m #服务器超时
timeout http-keep-alive 10s
timeout check 10s #心跳检测超时
maxconn 3000 #默认的最大连接数
#---------------------------------------------------------------------
# main frontend which proxys to the backends
#---------------------------------------------------------------------
frontend main *:5000 #haproxy服务器监听端口
acl url_static path_beg -i /static /p_w_picpaths /javascript /stylesheets
acl url_static path_end -i .jpg .gif .png .css .js
use_backend static if url_static
default_backend app
#---------------------------------------------------------------------
# static backend for serving up p_w_picpaths, stylesheets and such
#---------------------------------------------------------------------
backend static
balance roundrobin
#banlance roundrobin 轮询，balance source 保存session值，支持static-rr，leastconn，first，uri等参数
server static 127.0.0.1:4331 check
#---------------------------------------------------------------------
# round robin balancing between the various backends
#---------------------------------------------------------------------
backend app
balance roundrobin
server app1 127.0.0.1:5001 check
server app2 127.0.0.1:5002 check
server app3 127.0.0.1:5003 check
server app4 127.0.0.1:5004 check
接下来我们开始正式环境配置介绍：首先是安装Apache服务，然后配置显示页面：
Yum install httpd
安装完成
查看httpd 版本
接下来我们首先要为apache定义一个 默认的页面，方便区分
Vim /var/www/httml/index.html