Keepalived+Nginx+Tomcat sample code to implement high-availability Web cluster

Keepalived+Nginx+Tomcat to achieve high availability Web cluster 1. Nginx installation process 1. Download the Nginx installation package and install the dependent environment package (1) Install the C++ compilation environment yum -y install gcc #C++ (2) Install PCRE yum -y install pcre-devel (3) Install zlib yum -y install zlib-devel (4) Install Nginx Locate the nginx decompression file location and execute the compile and install command [root@localhost nginx-1.12.2]# pwd /usr/local/nginx/nginx-1.12.2 [root@localhost nginx-1.12.2]# ./configure && make && make install (5) Start Nginx After the installation is complete, first find the directory location where the installation is completed [root@localhost nginx-1.12.2]# whereis nginx nginx: /usr/local/nginx [root@localhost nginx-1.12.2]# Enter the Nginx subdirectory sbin and start Nginx [root@localhost sbin]# ls nginx [root@localhost sbin]# ./nginx & [1] 5768 [root@localhost sbin]# Check whether Nginx is started Or check the Nginx startup status through the process [root@localhost sbin]# ps -aux\|grep nginx root 5769 0.0 0.0 20484 608 ? Ss 14:03 0:00 nginx: master process ./nginx nobody 5770 0.0 0.0 23012 1620 ? S 14:03 0:00 nginx: worker process root 5796 0.0 0.0 112668 972 pts/0 R+ 14:07 0:00 grep --color=auto nginx [1]+ Completed ./nginx [root@localhost sbin]# At this point, Nginx is installed and started successfully. (6) Nginx quick start and boot configuration Edit the Nginx quick start script [ pay attention to the Nginx installation path , you need to change it according to your own NGINX path ] [root@localhost init.d]# vim /etc/rc.d/init.d/nginx #!/bin/sh # # nginx - this script starts and stops the nginx daemon # # chkconfig: -85 15 # description: Nginx is an HTTP(S) server, HTTP(S) reverse \ # Proxy and IMAP/POP3 proxy server # processname: nginx # config: /etc/nginx/nginx.conf # config: /usr/local/nginx/conf/nginx.conf # pidfile: /usr/local/nginx/logs/nginx.pid # Source function library. . /etc/rc.d/init.d/functions # Source networking configuration. . /etc/sysconfig/network # Check that networking is up. [ "$NETWORKING" = "no" ] && exit 0 nginx="/usr/local/nginx/sbin/nginx" prog=$(basename $nginx) NGINX_CONF_FILE="/usr/local/nginx/conf/nginx.conf" [ -f /etc/sysconfig/nginx ] && . /etc/sysconfig/nginx lockfile=/var/lock/subsys/nginx make_dirs() { # make required directories user=`$nginx -V 2>&1 \| grep "configure arguments:" \| sed 's/[^]--user=\([^ ]\)./\1/g' -` if [ -z "`grep $user /etc/passwd`" ]; then useradd -M -s /bin/nologin $user fi options=`$nginx -V 2>&1 \| grep 'configure arguments:'` for opt in $options; do if [ `echo $opt \| grep '.-temp-path'` ]; then value=`echo $opt \| cut -d "=" -f 2` if [ ! -d "$value" ]; then # echo "creating" $value mkdir -p $value && chown -R $user $value fi fi done } start() { [ -x $nginx ] \|\| exit 5 [ -f $NGINX_CONF_FILE ] \|\| exit 6 make_dirs echo -n $"Starting $prog: " daemon $nginx -c $NGINX_CONF_FILE retval=$? echo [ $retval -eq 0 ] && touch $lockfile return $retval } stop() { echo -n $"Stopping $prog: " killproc $prog -QUIT retval=$? echo [ $retval -eq 0 ] && rm -f $lockfile return $retval } restart() { #configtest \|\| return $? stop sleep 1 start } reload() { #configtest \|\| return $? echo -n $"Reloading $prog: " killproc $nginx -HUP RETVAL=$? echo } force_reload() { restart } configtest() { $nginx -t -c $NGINX_CONF_FILE } rh_status() { status $prog } rh_status_q() { rh_status >/dev/null 2>&1 } case "$1" in start) rh_status_q && exit 0 $1 ;; stop) rh_status_q \|\| exit 0 $1 ;; restart\|configtest) $1 ;; reload rh_status_q \|\| exit 7 $1 ;; force-reload force_reload ;; status) rh_status ;; condrestart\|try-restart) rh_status_q \|\| exit 0 ;; ) echo $"Usage: $0 {start\|stop\|status\|restart\|condrestart\|try-restart\|reload\|force-reload\|configtest}" exit 2 esac Authorize the startup script and add it to the startup [root@localhost init.d]# chmod -R 777 /etc/rc.d/init.d/nginx [root@localhost init.d]# chkconfig nginx Start Nginx [root@localhost init.d]# ./nginx start Add Nginx to system environment variables [root@localhost init.d]# echo 'export PATH=$PATH:/usr/local/nginx/sbin' >>/etc/profile && source /etc/profile Nginx command [service nginx (start\|stop\|restart)] [root@localhost init.d]# service nginx start Starting nginx (via systemctl): [ OK ] Tips: Quick Commands service nginx (start\|stop\|restart) 2. KeepAlived installation and configuration 1. Install Keepalived dependency environment yum install -y popt-devel yum install -y ipvsadm yum install -y libnl* yum install -y libnf* yum install -y openssl-devel 2. Compile Keepalived and install [root@localhost keepalived-1.3.9]# ./configure [root@localhost keepalived-1.3.9]# make && make install 3. Install Keepalive as a system service [root@localhost etc]# mkdir /etc/keepalived [root@localhost etc]# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/ Manually copy the default configuration file to the default path [root@localhost etc]# mkdir /etc/keepalived [root@localhost etc]# cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/ [root@localhost etc]# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/ Create a soft link for keepalived [root@localhost sysconfig]# ln -s /usr/local/keepalived/sbin/keepalived /usr/sbin/ Set Keepalived to start automatically at boot [root@localhost sysconfig]# chkconfig keepalived on NOTE: Forwarding request to 'systemctl enable keepalived.service'. Created symlink from /etc/systemd/system/multi-user.target.wants/keepalived.service to /usr/lib/systemd/system/keepalived.service Start the Keepalived service [root@localhost keepalived]# keepalived -D -f /etc/keepalived/keepalived.conf Shut down the Keepalived service [root@localhost keepalived]# killall keepalived 3. Cluster Planning and Construction Environmental preparation: CentOS 7.2 Keepalived Version 1.4.0 - December 29, 2017 Nginx Version: nginx/1.12.2 Tomcat Version:8 Cluster Planning Checklist

Keepalived+Nginx+Tomcat to achieve high availability Web cluster

1. Nginx installation process

1. Download the Nginx installation package and install the dependent environment package

(1) Install the C++ compilation environment

yum -y install gcc #C++

(2) Install PCRE

yum -y install pcre-devel

(3) Install zlib

yum -y install zlib-devel

(4) Install Nginx

Locate the nginx decompression file location and execute the compile and install command

[root@localhost nginx-1.12.2]# pwd
/usr/local/nginx/nginx-1.12.2
[root@localhost nginx-1.12.2]# ./configure && make && make install

(5) Start Nginx

After the installation is complete, first find the directory location where the installation is completed

[root@localhost nginx-1.12.2]# whereis nginx
nginx: /usr/local/nginx
[root@localhost nginx-1.12.2]#

Enter the Nginx subdirectory sbin and start Nginx

[root@localhost sbin]# ls
nginx
[root@localhost sbin]# ./nginx &
[1] 5768
[root@localhost sbin]#

Check whether Nginx is started

Or check the Nginx startup status through the process

[root@localhost sbin]# ps -aux|grep nginx
root 5769 0.0 0.0 20484 608 ? Ss 14:03 0:00 nginx: master process ./nginx
nobody 5770 0.0 0.0 23012 1620 ? S 14:03 0:00 nginx: worker process
root 5796 0.0 0.0 112668 972 pts/0 R+ 14:07 0:00 grep --color=auto nginx
[1]+ Completed ./nginx
[root@localhost sbin]#

At this point, Nginx is installed and started successfully.

(6) Nginx quick start and boot configuration

Edit the Nginx quick start script [ pay attention to the Nginx installation path , you need to change it according to your own NGINX path ]

[root@localhost init.d]# vim /etc/rc.d/init.d/nginx

#!/bin/sh
#
# nginx - this script starts and stops the nginx daemon
#
# chkconfig: -85 15
# description: Nginx is an HTTP(S) server, HTTP(S) reverse \
# Proxy and IMAP/POP3 proxy server
# processname: nginx
# config: /etc/nginx/nginx.conf
# config: /usr/local/nginx/conf/nginx.conf
# pidfile: /usr/local/nginx/logs/nginx.pid
 
# Source function library.
. /etc/rc.d/init.d/functions
 
# Source networking configuration.
. /etc/sysconfig/network
 
# Check that networking is up.
[ "$NETWORKING" = "no" ] && exit 0
nginx="/usr/local/nginx/sbin/nginx"
prog=$(basename $nginx)
NGINX_CONF_FILE="/usr/local/nginx/conf/nginx.conf"
[ -f /etc/sysconfig/nginx ] && . /etc/sysconfig/nginx
lockfile=/var/lock/subsys/nginx
 
make_dirs() {
 # make required directories
 user=`$nginx -V 2>&1 | grep "configure arguments:" | sed 's/[^*]*--user=\([^ ]*\).*/\1/g' -`
 if [ -z "`grep $user /etc/passwd`" ]; then
 useradd -M -s /bin/nologin $user
 fi
 options=`$nginx -V 2>&1 | grep 'configure arguments:'`
 for opt in $options; do
 if [ `echo $opt | grep '.*-temp-path'` ]; then
 value=`echo $opt | cut -d "=" -f 2`
 if [ ! -d "$value" ]; then
 # echo "creating" $value
 mkdir -p $value && chown -R $user $value
 fi
 fi
 done
}
 
start() {
 [ -x $nginx ] || exit 5
 [ -f $NGINX_CONF_FILE ] || exit 6
 make_dirs
 echo -n $"Starting $prog: "
 daemon $nginx -c $NGINX_CONF_FILE
 retval=$?
 echo
 [ $retval -eq 0 ] && touch $lockfile
 return $retval
}
 
stop() {
 echo -n $"Stopping $prog: "
 killproc $prog -QUIT
 retval=$?
 echo
 [ $retval -eq 0 ] && rm -f $lockfile
 return $retval
}
 
restart() {
 #configtest || return $?
 stop
 sleep 1
 start
}
 
reload() {
 #configtest || return $?
 echo -n $"Reloading $prog: "
 killproc $nginx -HUP
 RETVAL=$?
 echo
}
 
force_reload() {
 restart
}
 
configtest() {
 $nginx -t -c $NGINX_CONF_FILE
}
 
rh_status() {
 status $prog
}
 
rh_status_q() {
 rh_status >/dev/null 2>&1
}
 
case "$1" in
start)
rh_status_q && exit 0
$1
;;
stop)
 
rh_status_q || exit 0
$1
;;
restart|configtest)
$1
;;
reload
rh_status_q || exit 7
$1
;;
force-reload
force_reload
;;
status)
rh_status
;;
condrestart|try-restart)
rh_status_q || exit 0
;;
*)
echo $"Usage: $0 {start|stop|status|restart|condrestart|try-restart|reload|force-reload|configtest}"
exit 2
esac

Authorize the startup script and add it to the startup

[root@localhost init.d]# chmod -R 777 /etc/rc.d/init.d/nginx 
[root@localhost init.d]# chkconfig nginx

Start Nginx

[root@localhost init.d]# ./nginx start

Add Nginx to system environment variables

[root@localhost init.d]# echo 'export PATH=$PATH:/usr/local/nginx/sbin' >>/etc/profile && source /etc/profile

Nginx command [service nginx (start|stop|restart)]

[root@localhost init.d]# service nginx start
Starting nginx (via systemctl): [ OK ]

Tips: Quick Commands

service nginx (start|stop|restart)

2. KeepAlived installation and configuration

1. Install Keepalived dependency environment

yum install -y popt-devel  
yum install -y ipvsadm
yum install -y libnl*
yum install -y libnf*
yum install -y openssl-devel

2. Compile Keepalived and install

[root@localhost keepalived-1.3.9]# ./configure
[root@localhost keepalived-1.3.9]# make && make install

3. Install Keepalive as a system service

[root@localhost etc]# mkdir /etc/keepalived
[root@localhost etc]# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/

Manually copy the default configuration file to the default path

[root@localhost etc]# mkdir /etc/keepalived
[root@localhost etc]# cp /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/
[root@localhost etc]# cp /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/

Create a soft link for keepalived

[root@localhost sysconfig]# ln -s /usr/local/keepalived/sbin/keepalived /usr/sbin/

Set Keepalived to start automatically at boot

[root@localhost sysconfig]# chkconfig keepalived on
NOTE: Forwarding request to 'systemctl enable keepalived.service'.
Created symlink from /etc/systemd/system/multi-user.target.wants/keepalived.service to /usr/lib/systemd/system/keepalived.service

Start the Keepalived service

[root@localhost keepalived]# keepalived -D -f /etc/keepalived/keepalived.conf

Shut down the Keepalived service

[root@localhost keepalived]# killall keepalived

3. Cluster Planning and Construction

Environmental preparation:

CentOS 7.2

Keepalived Version 1.4.0 - December 29, 2017

Nginx Version: nginx/1.12.2

Tomcat Version:8

Cluster Planning Checklist

Virtual Machines	IP	illustrate
Keepalived+Nginx1[Master]	192.168.43.101	Nginx Server 01
Keeepalived+Nginx[Backup]	192.168.43.102	Nginx Server 02
Tomcat01	192.168.43.103	Tomcat Web Server01
Tomcat02	192.168.43.104	Tomcat Web Server02
VIP	192.168.43.150	Virtual Drift IP

1. Change the Tomcat default welcome page to identify the switch to Web

Change the ROOT/index.jsp information of the TomcatServer01 node, add the Tomcat IP address, and add the Nginx value, that is, modify the node 192.168.43.103 information as follows:

<div id="asf-box">
 <h1>${pageContext.servletContext.serverInfo}(192.168.224.103)<%=request.getHeader("X-NGINX")%></h1>
</div>

Change the ROOT/index.jsp information of the TomcatServer02 node, add the Tomcat IP address, and add the Nginx value, that is, modify the node 192.168.43.104 information as follows:

<div id="asf-box">
 <h1>${pageContext.servletContext.serverInfo}(192.168.224.104)<%=request.getHeader("X-NGINX")%></h1>
</div>

2. Start the Tomcat service and check the Tomcat service IP information. At this time, Nginx is not started, so the request-header does not contain Nginx information.

3. Configure Nginx proxy information

1. Configure the Master node [192.168.43.101] proxy information

upstream tomcat {
 server 192.168.43.103:8080 weight=1;
 server 192.168.43.104:8080 weight=1;
}
server{
 location / {
  proxy_pass http://tomcat;
 proxy_set_header X-NGINX "NGINX-1";
 }
 #......Others omitted}

2. Configure the Backup node [192.168.43.102] proxy information

upstream tomcat {
 server 192.168.43.103:8080 weight=1;
 server 192.168.43.104:8080 weight=1;
}
server{
 location / {
  proxy_pass http://tomcat;
 proxy_set_header X-NGINX "NGINX-2";
 }
 #......Others omitted}

3. Start the Master node Nginx service

[root@localhost init.d]# service nginx start
Starting nginx (via systemctl): [ OK ]

At this time, when you visit 192.168.43.101, you can see that the Tcomat nodes 103 and 104 are displayed alternately, indicating that the Nginx service has loaded the request to two tomcats.

4. Similarly, configure the Backup [192.168.43.102] Nginx information. After starting Nginx, visit 192.168.43.102 and you can see that the Backup node has played a load role.

4. Configure Keepalived script information

1. Add the check_nginx.sh file to the /etc/keepalived directory on the Master and Slave nodes to detect the inventory status of Nginx and add the keepalived.conf file

The check_nginx.sh file information is as follows:

#!/bin/bash
#Time variable, used to record logs d=`date --date today +%Y%m%d_%H:%M:%S`
# Calculate the number of nginx processes n=`ps -C nginx --no-heading|wc -l`
#If the process is 0, start nginx and check the number of nginx processes again.
#If it is still 0, it means that nginx cannot be started, and you need to turn off keepalived
if [ $n -eq "0" ]; then
  /etc/rc.d/init.d/nginx start
  n2=`ps -C nginx --no-heading|wc -l`
  if [ $n2 -eq "0" ]; then
    echo "$d nginx down,keepalived will stop" >> /var/log/check_ng.log
    systemctl stop keepalived
  fi
fi

After adding, authorize the check_nginx.sh file so that the script can obtain execution permissions.

[root@localhost keepalived]# chmod -R 777 /etc/keepalived/check_nginx.sh

2. Add the keepalived.conf file in the /etc/keepalived directory of the Master node. The specific information is as follows:

vrrp_script chk_nginx { 
 script "/etc/keepalived/check_nginx.sh" //Script interval 2 to detect nginx process 
 weight -20 
} 

global_defs { 
 notification_email { 
  //You can add email reminders} 
} 
vrrp_instance VI_1 { 
 state MASTER #Indicates the state is MASTER and the backup machine is BACKUP
 interface ens33 #Set the network card bound to the instance (check ip addr, need to bind according to personal network card)
 virtual_router_id 51 #The virtual_router_id must be the same in the same instance mcast_src_ip 192.168.43.101 
 priority 250 #MASTER has a higher priority than BACKUP, for example, BACKUP is 240 
 advert_int 1 #Time interval between synchronization checks between MASTER and BACKUP load balancers, in seconds nopreempt #Non-preemptive mode authentication { #Set authentication auth_type PASS #Master-slave server authentication method auth_pass 123456 
 } 
 track_script { 
  check_nginx 
 } 
 virtual_ipaddress { #Set VIP
  192.168.43.150 #You can have multiple virtual IPs, just wrap the line} 
}

3. Add the keepalived.conf configuration file in the etc/keepalived directory of the Backup node

The information is as follows:

vrrp_script chk_nginx { 
 script "/etc/keepalived/check_nginx.sh" //Script interval 2 to detect nginx process 
 weight -20 
} 

global_defs { 
 notification_email { 
  //You can add email reminders} 
} 
vrrp_instance VI_1 { 
 state BACKUP #Indicates the state is MASTER and the backup machine is BACKUP
 interface ens33 #Set the network card bound to the instance (view by ip addr)
 virtual_router_id 51 #The virtual_router_id must be the same in the same instance mcast_src_ip 192.168.43.102 
 priority 240 #MASTER has a higher priority than BACKUP. For example, BACKUP is 240. 
 advert_int 1 #Time interval between synchronization checks between MASTER and BACKUP load balancers, in seconds nopreempt #Non-preemptive mode authentication { #Set authentication auth_type PASS #Master-slave server authentication method auth_pass 123456 
 } 
 track_script { 
  check_nginx 
 } 
 virtual_ipaddress { #Set VIP
  192.168.43.150 #You can have multiple virtual IPs, just wrap the line} 
}

Tips: Some notes on configuration information

state - The master server needs to be configured as MASTER and the slave server needs to be configured as BACKUP
interface - This is the name of the network card. I am using VM12.0, so the network card here is named ens33
mcast_src_ip - configure the actual IP address of each
priority - The priority of the master server must be higher than that of the slave server. Here, the master server is configured as 250 and the slave server is configured as 240.
virtual_ipaddress - configures a virtual IP (192.168.43.150)
authentication - auth_pass must be consistent between the master and slave servers, keepalived relies on this to communicate
virtual_router_id - The master and slave servers must have the same id

5. Cluster High Availability (HA) Verification

Step 1 Start the Keepalived and Nginx services on the Master machine

[root@localhost keepalived]# keepalived -D -f /etc/keepalived/keepalived.conf
[root@localhost keepalived]# service nginx start

View service startup process

[root@localhost keepalived]# ps -aux|grep nginx
root 6390 0.0 0.0 20484 612 ? Ss 19:13 0:00 nginx: master process /usr/local/nginx/sbin/nginx -c /usr/local/nginx/conf/nginx.conf
nobody 6392 0.0 0.0 23008 1628 ? S 19:13 0:00 nginx: worker process
root 6978 0.0 0.0 112672 968 pts/0 S+ 20:08 0:00 grep --color=auto nginx

View the Keepalived startup process

[root@localhost keepalived]# ps -aux|grep keepalived
root 6402 0.0 0.0 45920 1016 ? Ss 19:13 0:00 keepalived -D -f /etc/keepalived/keepalived.conf
root 6403 0.0 0.0 48044 1468 ? S 19:13 0:00 keepalived -D -f /etc/keepalived/keepalived.conf
root 6404 0.0 0.0 50128 1780 ? S 19:13 0:00 keepalived -D -f /etc/keepalived/keepalived.conf
root 7004 0.0 0.0 112672 976 pts/0 S+ 20:10 0:00 grep --color=auto keepalived

Use ip add to check the virtual IP binding status. If 192.168.43.150 node information appears, it is bound to the Master node.

[root@localhost keepalived]# ip add
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 inet 127.0.0.1/8 scope host lo
  valid_lft forever preferred_lft forever
 inet6 ::1/128 scope host 
  valid_lft forever preferred_lft forever
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
 link/ether 00:0c:29:91:bf:59 brd ff:ff:ff:ff:ff:ff
 inet 192.168.43.101/24 brd 192.168.43.255 scope global ens33
  valid_lft forever preferred_lft forever
 inet 192.168.43.150/32 scope global ens33
  valid_lft forever preferred_lft forever
 inet6 fe80::9abb:4544:f6db:8255/64 scope link 
  valid_lft forever preferred_lft forever
 inet6 fe80::b0b3:d0ca:7382:2779/64 scope link tentative dadfailed 
  valid_lft forever preferred_lft forever
 inet6 fe80::314f:5fe7:4e4b:64ed/64 scope link tentative dadfailed 
  valid_lft forever preferred_lft forever
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN qlen 1000
 link/ether 52:54:00:2b:74:aa brd ff:ff:ff:ff:ff:ff
 inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
  valid_lft forever preferred_lft forever
4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN qlen 1000
 link/ether 52:54:00:2b:74:aa brd ff:ff:ff:ff:ff:ff

Step 2 Start the Nginx service and Keepalived service on the Backup node and check the service startup status. If a virtual IP appears on the Backup node, there is a problem with the Keepalived configuration file. This situation is called split-brain.

[root@localhost keepalived]# clear
[root@localhost keepalived]# ip add
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN qlen 1
 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
 inet 127.0.0.1/8 scope host lo
  valid_lft forever preferred_lft forever
 inet6 ::1/128 scope host 
  valid_lft forever preferred_lft forever
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
 link/ether 00:0c:29:14:df:79 brd ff:ff:ff:ff:ff:ff
 inet 192.168.43.102/24 brd 192.168.43.255 scope global ens33
  valid_lft forever preferred_lft forever
 inet6 fe80::314f:5fe7:4e4b:64ed/64 scope link 
  valid_lft forever preferred_lft forever
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN qlen 1000
 link/ether 52:54:00:2b:74:aa brd ff:ff:ff:ff:ff:ff
 inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
  valid_lft forever preferred_lft forever
4: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast master virbr0 state DOWN qlen 1000
 link/ether 52:54:00:2b:74:aa brd ff:ff:ff:ff:ff:ff

Step 3 Verify the service

Browse and force refresh the address multiple times: http://192.168.43.150. You can see that 103 and 104 are displayed alternately multiple times, and Nginx-1 is displayed, indicating that the Master node is forwarding the web service.

Step 4 Close the Master keepalived service and Nginx service, access the Web service to observe the service transfer status

[root@localhost keepalived]# killall keepalived
[root@localhost keepalived]# service nginx stop

At this time, forcefully refresh 192.168.43.150 and find that the page displays 103 and 104 alternately and displays Nginx-2. The VIP has been transferred to 192.168.43.102, proving that the service automatically switches to the backup node.

Step 5 Start the Master Keepalived service and Nginx service

At this time, we verified again that the VIP has been recaptured by the Master, and the page displays 103 and 104 alternately. At this time, Nginx-1 is displayed.

4. Keepalived preemptive mode and non-preemptive mode

Keepalived's HA is divided into preemptive mode and non-preemptive mode. In preemptive mode, after the MASTER recovers from a failure, it will preempt the VIP from the BACKUP node. The non-preemptive mode means that after the MASTER is restored, the VIP after the BACKUP is upgraded to the MASTER will not be preempted.

Non-preemptive mode configuration:

1> Added the nopreempt instruction to each of the two nodes under the vrrp_instance block, indicating that no VIP competition is required

2> The state of the nodes is BACKUP. After both keepalived nodes are started, they are in BACKUP state by default. After sending multicast information, both parties will elect a MASTER based on priority. Since nopreempt is configured for both, the MASTER will not preempt the VIP after recovering from a failure. This will avoid service delays that may be caused by VIP switching.

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