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一、Keepalived工作原理

Keepalived可提供VRRP以及health-check功能，可以只用它提供雙機浮動的vip（VRRP虛擬路由功能），這樣可以簡單實現(xiàn)一個雙機熱備高可用功能。

Keepalived是以VRRP虛擬路由冗余協(xié)議為基礎(chǔ)實現(xiàn)高可用的，可以認為是實現(xiàn)路由器高可用的協(xié)議，即將N臺提供相同功能的路由器組成一個路由器組，這個組里面有一個master和多個backup，master上面有一個對外提供服務(wù)的vip（該路由器所在局域網(wǎng)內(nèi)其他機器的默認路由為該vip），master會發(fā)組播，當(dāng)backup收不到VRRP包時就認為master宕掉了，這時就需要根據(jù)VRRP的優(yōu)先級來選舉一個backup當(dāng)master。這樣的話就可以保證路由器的高可用了。

下載地址：（復(fù)制鏈接至瀏覽器中瀏覽）

https://www.keepalived.org/download.html
https://github.com/acassen/keepalived

Keepalived工作在TCP/IP參考模型的三層、四層、五層（物理層，鏈路層）：

網(wǎng)絡(luò)層（3）：Keepalived通過ICMP協(xié)議向服務(wù)器集群中的每一個節(jié)點發(fā)送一個ICMP數(shù)據(jù)包(有點類似與Ping的功能)，如果某個節(jié)點沒有返回響應(yīng)數(shù)據(jù)包，那么認為該節(jié)點發(fā)生了故障，Keepalived將報告這個節(jié)點失效，并從服務(wù)器集群中剔除故障節(jié)點。
傳輸層（4）：Keepalived在傳輸層里利用了TCP協(xié)議的端口連接和掃描技術(shù)來判斷集群節(jié)點的端口是否正常，比如對于常見的WEB服務(wù)器80端口。或者SSH服務(wù)22端口，Keepalived一旦在傳輸層探測到這些端口號沒有數(shù)據(jù)響應(yīng)和數(shù)據(jù)返回，就認為這些端口發(fā)生異常，然后強制將這些端口所對應(yīng)的節(jié)點從服務(wù)器集群中剔除掉。
應(yīng)用層（5）：Keepalived的運行方式也更加全面化和復(fù)雜化，用戶可以通過自定義Keepalived工作方式，例如：可以通過編寫程序或者腳本來運行Keepalived，而Keepalived將根據(jù)用戶的設(shè)定參數(shù)檢測各種程序或者服務(wù)是否允許正常，如果Keepalived的檢測結(jié)果和用戶設(shè)定的不一致時，Keepalived將把對應(yīng)的服務(wù)器從服務(wù)器集群中剔除。

二、架構(gòu)

2.1 主機規(guī)劃

2.2 架構(gòu)圖

三、環(huán)境準(zhǔn)備

3.1 關(guān)閉防火墻和selinux

[root@localhost ~]# systemctl stop firewalld
[root@localhost keepalived]# vi /etc/selinux/config
SELINUX=disabled
[root@localhost keepalived]# getenforce
Disabled

3.2 安裝Keepalived

[root@localhost ~]# yum install gcc openssl openssl‐devel libnl libnl‐devel ipvsadm -y
[root@localhost ~]# cd /usr/local/src/
[root@localhost src]# tar -zxf keepalived-2.2.4.tar.gz 
[root@localhost src]# cd keepalived-2.2.4
[root@localhost keepalived-2.2.4] ./configure --prefix=/usr/local/keepalived
[root@localhost keepalived-2.2.4] make && make install
[root@localhost keepalived]#  cd /usr/local/keepalived
[root@localhost keepalived]# 
ln -s /usr/local/src/keepalived-2.2.4/keepalived/etc/init.d/keepalived /etc/init.d/
[root@localhost keepalived]# ln -s /usr/local/keepalived/etc/sysconfig/keepalived /etc/sysconfig/
[root@localhost keepalived]# ln -s /usr/local/keepalived/sbin/keepalived /usr/local/sbin/
[root@localhost keepalived]# mkdir /etc/keepalived/
[root@localhost keepalived]# ln -s  /usr/local/keepalived/etc/keepalived/keepalived.conf /etc/keepalived/
[root@localhost ~]# cat  /etc/keepalived/keepalived.conf 

[root@localhost keepalived-2.2.4]# systemctl start keepalived
[root@localhost keepalived-2.2.4]# systemctl status keepalived

3.3?PostgreSQL數(shù)據(jù)庫異步主從流復(fù)制搭建

192.168.254.128服務(wù)器上配置:

1、創(chuàng)建流復(fù)制用戶

postgres=# create user replia replication superuser password ‘123qwert’;

給superuser權(quán)限是為了后面做pg_rewind操作。

2、數(shù)據(jù)目錄下配置pg_hba.conf文件添加（192.168.254.129也需要添加）

? ? host replication all 192.168.254.1/24 md5

3、配置環(huán)境變量

[postgres@localhost pg_data]$ cat ~/.bash_profile 
# .bash_profile
# Get the aliases and functions
if [ -f ~/.bashrc ]; then 	. ~/.bashrc; fi
PATH=$PATH:$HOME/.local/bin:$HOME/bin
export PATH
export PGHOME=/usr/local/pgsql
export LD_LIBRARY_PATH=$PGHOME/lib:/lib64:/usr/lib64:/usr/local/lib64:/lib:/usr/lib:/usr/local/lib:$LD_LIBRARY_PATH
export DATE=`date +"%Y%m%d%H%M"`
export PATH=$PGHOME/bin:$PATH:.
export MANPATH=$PGHOME/share/man:$MANPATH
export PGUSER=postgres
export PGDATA=/data/pg_data
export PGDATABASE=postgres
alias rm='rm -i'
alias ll='ls -lh'
export LANG="zh_CN.UTF8"

在192.168.254.129上進行：

4、~/.bash_profile 和上面輸入一樣的內(nèi)容

5、制作基礎(chǔ)備份

 [postgres@localhost ~]$ pg_basebackup -h192.168.254.128 -Ureplia -R -Fp -P --verbose ?-c fast -D /data/pg_data

6、啟動從庫

 [postgres@localhost ~]$ pg_ctl -D /data/pg_data/ start

192.168.254.128上查看主庫信息：

7、查看主庫信息

 postgres=# select * from pg_stat_replication ;

3.4 PostgreSQL數(shù)據(jù)庫配置

創(chuàng)建數(shù)據(jù)庫Keepalived，并且創(chuàng)建表探測表sr_delay，后續(xù)Keepalived探測，刷新sr_delay表的last_alive字段為當(dāng)前探測時間。這張表用來判斷主備延遲情況，數(shù)據(jù)庫故障切換時會用到這張表。

數(shù)據(jù)庫配置：

postgres=# create user keepalived password '123qwert' CONNECTION LIMIT 4 ;
CREATE ROLE
postgres=# create database keepalived owner keepalived;
CREATE DATABASE
postgres=# \c keepalived keepalived
You are now connected to database "keepalived" as user "keepalived".
keepalived=> create table sr_delay(id int4, last_alive timestamp(0) without time zone);
CREATE TABLE

表sr_delay只允許寫入一條記錄，并且不允許刪除此表數(shù)據(jù)，通過觸發(fā)器實現(xiàn)。創(chuàng)建觸發(fā)器函數(shù)，如下所示：

CREATE FUNCTION cannt_delete () 
RETURNS trigger 
LANGUAGE plpgsql AS $$ 
BEGIN 
RAISE EXCEPTION 'Table sr_delay can not delete !';
 END; 
$$;

創(chuàng)建觸發(fā)器：

CREATE TRIGGER trigger_sr_delay_del 
BEFORE DELETE ON sr_delay 
FOR EACH ROW EXECUTE PROCEDURE cannt_delete() ; 
CREATE TRIGGER trigger_sr_delay_tru BEFORE TRUNCATE ON sr_delay FOR STATEMENT EXECUTE PROCEDURE cannt_delete() ;

插入數(shù)據(jù)：

 INSERT INTO sr_delay VALUES(1,now()) ;

參數(shù)部分：

hot_standby = on
wal_log_hints = on 
archive_mode=on
archive_command='test ! -f /data/pg_archive/%f && cp %p /data/pg_archive/%f'

后續(xù)Keepalived會每隔指定時間探測PostgreSQL數(shù)據(jù)庫存活，并且以Keepalived用戶登錄Keepalived數(shù)據(jù)庫刷新這張表，配置主備庫pg_hba.conf，增加如下內(nèi)容：

host    keepalived    keepalived        192.168.254.128/32      md5
host    keepalived    keepalived        192.168.254.129/32      md5

隨后pg_ctl reload 操作使配置生效。

3.5 Keepalived 配置

[root@localhost ~]# cat /etc/keepalived/keepalived.conf 
! Configuration File for keepalived
global_defs {
   # 郵件通知信息
   notification_email {
     # 定義收件人
    [email protected] 
   }
   # 定義發(fā)件人
   notification_email_from [email protected]
   # SMTP服務(wù)器地址
   smtp_server 192.168.254.128
   smtp_connect_timeout 30
   # 路由器標(biāo)識，一般不用改，也可以寫成每個主機自己的主機名
   router_id LVS_DEVEL
   vrrp_skip_check_adv_addr
   vrrp_strict
   vrrp_garp_interval 0
   vrrp_gna_interval 0
}

# 定義用于實例執(zhí)行的腳本內(nèi)容，比如可以在線降低優(yōu)先級，用于強制切換
vrrp_script check_pg_alived { 
script "/data/scripts/pg_monitor.sh" 
interval 10 
fall 3 
}

# 一個vrrp_instance就是定義一個虛擬路由器的，實例名稱
vrrp_instance VI_1 {
    # 定義初始狀態(tài)，可以是MASTER或者BACKUP
    state MASTER
    #非搶占模式
    nopreempt
    # 工作接口，通告選舉使用哪個接口進行
    interface ens33
    # 虛擬路由ID，如果是一組虛擬路由就定義一個ID，如果是多組就要定義多個，而且這個虛擬
    # ID還是虛擬MAC最后一段地址的信息，取值范圍0-255
    virtual_router_id 51
    #權(quán)重 如果你上面定義了MASTER,這里的優(yōu)先級就需要定義的比其他的高
    priority 100
    #通告頻率 單位s
    advert_int 1
    # 通信認證機制，這里是明文認證還有一種是加密認證
    authentication {
        auth_type PASS
        auth_pass 1111
    }
    # 設(shè)置虛擬VIP地址
    virtual_ipaddress {
        192.168.254.11
    }
    # 追蹤腳本，通常用于去執(zhí)行上面的vrrp_script定義的腳本內(nèi)容
    track_script {
      check_pg_alived
    }
   # 如果主機狀態(tài)變成Master|Backup|Fault之后會去執(zhí)行的通知腳本，腳本要自己寫
    notify_master "/data/scripts/failover.sh"
    notify_fault  "/data/scripts/fault.sh"
}

以上是Keepalived主節(jié)點的配置，Keepalived備節(jié)點的priority參數(shù)改成90 ，state改為BACKUP，以及smtp_server 改為192.168.254.129，其余參數(shù)配置一樣。

3.6 數(shù)據(jù)庫監(jiān)控腳本

[postgres@localhost scripts]$ cat /data/scripts/pg_monitor.sh 
#!/bin/bash 
# 配置環(huán)境變量 
pgport=5432 
pguser=keepalived 
pgdb=keepalived 
pgpwd='123qwert'
LANG=en_US.utf8 
PGHOME=/usr/local/pgsql/ 
LD_LIBRARY_PATH=$PGHOME/lib:/lib64:/usr/lib64:/usr/local/lib64:/lib:/usr/lib:/usr/local/lib 
PATH=$PGHOME/bin:$PATH:.
MONITOR_LOG="/data/scripts/pg_monitor.log" 
SQL1="UPDATE sr_delay SET last_alive= now();" 
SQL2='SELECT 1;' 
keeplognums=30000

#pg_port_status=`lsof ‐i :$pgport | grep LISTEN | wc ‐l` 
#pg_port_status=`ps ‐ef | grep LISTEN | wc ‐l` 
#if [ $pg_port_status ‐lt 1 ];then 
# echo ‐e `date +"%F %T"` "Error: The postgreSQL is not running,please chec k the postgreSQL server status!" >> $LOGFILE 
# exit 1 
#fi 

#此腳本不檢查備庫存活狀態(tài)，如果是各庫則退出 

standby_flg=`psql -p$pgport -Upostgres -At -c "SELECT pg_is_in_recovery();"` 
if [ ${standby_flg} == 't' ]; 
then 
 echo ‐e "`date +%F\ %T`: This is a standby database, exit!\n" > $MONITOR_LOG 
 exit 0 
fi
export PGPASSWORD=$pgpwd
#主庫更新sr_delay 表 
echo $SQL1 | psql -At -p $pgport -U $pguser -d $pgdb >> $MONITOR_LOG 
#判斷主庫是否可用
echo $SQL2 | psql -At -p $pgport -U $pguser -d $pgdb 
if [ $? -eq 0 ] ;
then 
 echo -e "`date +%F\ %T`：Primary db is health." >> $MONITOR_LOG 
 exit 0 
else 
 echo -e "`date +%F\ %T`:Attention: Primary db is not health!" >> $MONITOR_LOG 
 exit 1 
fi

#日志保留 keeplognums 行
if [ ! -f ${MONITOR_LOG} ] ;then touch ${MONITOR_LOG};fi 
lognums=`cat ${MONITOR_LOG} |wc -l`
catnum=$((${lognums} -${keeplognums}))
if [[ $lognums -gt ${keeplognums} ]] ; then sed -i "1,${catnum}d" ${MONITOR_LOG}; fi

此腳本每隔10秒執(zhí)行一次，執(zhí)行頻率由keepalived.conf配置文件中interval參數(shù)設(shè)置，腳本主要作用為：

檢測主庫是否存活。
更新sr_delay表last_alive字段為當(dāng)前探測時間。

[postgres@localhost scripts]$ cat /data/scripts/failover.sh 
#!/bin/bash 
export PGPORT=5432 
export PGUSER=keepalived 
export PG_OS_USER=postgres 
export PGDBNAME=keepalived 
export LANG=en_US.UTF-8 
export PGPATH=/usr/local/pgsql/bin/ 
export PATH=$PATH:$PGPATH 
export PGMIP=127.0.0.1 
LOGFILE='/data/scripts/failover.log'
# 主備數(shù)據(jù)庫同步時延，單位為秒 
sr_allowed_delay_time=100

SQL1='select pg_is_in_recovery from pg_is_in_recovery();' 
SQL2="select count(1) as delay_time from sr_delay where now()<(last_alive + interval '${sr_allowed_delay_time} seconds');"
#SQL2="select count(1) as delay_time from sr_delay where now()<(last_alive + interval '100 seconds');" 
sleep $sr_allowed_delay_time
db_role=`echo $SQL1 | psql -At -p $PGPORT -U $PGUSER -d $PGDBNAME -w` 
db_sr_delaytime=`echo $SQL2 | psql -p $PGPORT -d $PGDBNAME -U $PGUSER -At -w` 
SWITCH_COMMAND='pg_ctl promote -D /data/pg_data/' 
# 如果為備庫，且延遲大于指定時間則切換為主庫

if [ ${db_role} == 'f' ];
then 
	echo -e `date +"%F %T"` "Attention:The current postgreSQL DB is master database,cannot switched!" >> $LOGFILE 
	exit 0 
fi

if [ $db_sr_delaytime -gt 0 ];
then 
	echo -e `date +"%F %T"` "Attention:The current master database is health,the standby DB cannot switched!" >> $LOGFILE 
	exit 0 
fi

if [ !$db_sr_delaytime ];
then 
	echo -e `date +"%F %T"` "Attention:The current database is statndby,ready to switch master database!" >> $LOGFILE 
	su - $PG_OS_USER -c "$SWITCH_COMMAND" 
elif [ $? -eq 0 ];
then
	echo -e `date +"%F %T"` "success:The current standby database successed to switched the primary PG database !" >> $LOGFILE 
	exit 0 
else 
	echo -e `date +"%F %T"` "Error: the standby database failed to switch the primary PG database !,pelease checked it!" >> $LOGFILE 
	exit 1
fi

[postgres@localhost scripts]$ cat /data/scripts/fault.sh
#!/bin/bash
GFILE=/data/scripts/pg_db_fault.log 
PGPORT=5432 
PGMIP=192.168.254.128
echo -e `date +"%F %T"` "Error:Because of the priamry DB happend some unknown problem,So turn off the PostgreSQL Database!" >> $LOGFILE 

PGPID="`head -n1 /data/pg_data/postmaster.pid`" 

systemctl stop keepalived 

kill -9 $PGPID 
if [ $? -eq 0 ] ;
then 
	echo -e `date +"%F %T"` "Error:Because of the priamry DB happend some unknown problem,So turn off the PostgreSQL Database!" >> $LOGFILE
	systemctl stop keepalived 
	exit 1 
fi

[postgres@localhost scripts]$ chmod 755 /data/scripts/pg_monitor.sh /data/scripts/failover.sh /data/scripts/fault.sh

四、切換演練

4.1 在192.168.254.128上停掉數(shù)據(jù)庫

[root@localhost ~]# su - postgres
[postgres@localhost ~]$ pg_ctl -D /data/pg_data/ stop

查看192.168.254.129上的數(shù)據(jù)庫狀態(tài)：

[postgres@localhost ~]$ psql
psql (13.3)
Type "help" for help.
postgres=# insert into t5 (name) values ('b002');
INSERT 0 1

修復(fù)192.168.254.128。

使用pg_rewind 同步新主庫的數(shù)據(jù)到原主庫：

pg_rewind -R --target-pgdata '/data/pg_data' --source-server 'host=192.168.254.129 port=5432 user=replia password=123qwert dbname=postgres'

如果這個地方咱們的wal日志已經(jīng)被覆蓋了了很多，那么就需要將我們的備份日志/data/pg_archive/給scp過來。

[postgres@localhost ~]$ scp [email protected]:/data/pg_archive/00000002*  /data/pg_archive/

(此時需要注意新主和備上面TimeLineID的差異。并且這種情況需要在配置文件中加上：

restore_command='cp /data/pg_archive/%f %p'

）

啟動數(shù)據(jù)庫，然后檢查主備wal sender和receiver是否正常：

[postgres@localhost ~]$ pg_ctl -D /data/pg_data/ start
[postgres@localhost ~]$ ps axu |grep walreceiver
postgres  53474  0.0  0.2 342008  2136 ?        Ss   14:45   0:01 postgres: walreceiver streaming 1/4A036EF0

192.168.254.128上啟動Keepalived，查看Keepalived狀態(tài)：

[root@localhost ~]# systemctl  start keepalived
[root@localhost ~]# systemctl  status keepalived

4.2 再次切換：

在做切換前，先要檢查192.168.254.128和192.168.254.129上面的Keepalived正常以及vip和主從正常，在192.168.254.129上停掉數(shù)據(jù)庫:

[postgres@localhost ~]$ pg_ctl -D /data/pg_data/ stop -mf

查看192.168.254.128上的數(shù)據(jù)庫狀態(tài)：

[postgres@localhost pg_data]$ psql
psql (13.3)
Type "help" for help.
postgres=# insert into t5 (name) values ('b005');
INSERT 0 1

修復(fù)192.168.254.129。

使用pg_rewind 同步新主庫的數(shù)據(jù)到原主庫：

pg_rewind -R --target-pgdata '/data/pg_data' --source-server 'host=192.168.254.128 port=5432 user=replia password=123qwert dbname=postgres'

如果這個地方咱們的wal日志已經(jīng)被覆蓋了了很多，那么就需要將我們的備份日志/data/pg_archive/給scp過來。

[postgres@localhost ~]$ scp [email protected]:/data/pg_archive/00000003* ?/data/pg_archive/ ?

(此時需要注意新主和備上面TimeLineID的差異。并且這種情況需要在配置文件中加上：

restore_command='cp /data/pg_archive/%f %p'

）

啟動數(shù)據(jù)庫，然后檢查主備wal sender和receiver是否正常：

[postgres@localhost ~]$ pg_ctl -D /data/pg_data/ start
[postgres@localhost ~]$ ps axu |grep walreceiver

192.168.254.129上啟動Keepalived，查看Keepalived狀態(tài)：

[root@localhost ~]# systemctl  start keepalived
[root@localhost ~]# systemctl  status keepalived

五、總結(jié)

1、可以完善failover時自己的延遲切換邏輯。

2、可以完善pg_rewind的實現(xiàn)，用腳本代替手動方式。

3、Keepalived較為靈活，能夠在腳本上添加更多校驗和自己的規(guī)則。

墨天輪原文鏈接：https://www.modb.pro/db/113653?sjhy（復(fù)制到瀏覽器或者點擊“閱讀原文”立即查看）
關(guān)于作者
向前龍??，云和恩墨PG技術(shù)顧問，擁有OGCA、PGCE證書。

END

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用Keepalived實現(xiàn)PostgreSQL高可用