7.3. Pgpool-II + Watchdog Setup Example

This section shows an example of streaming replication configuration using Pgpool-II. In this example, we use 3 Pgpool-II servers to manage PostgreSQL servers to create a robust cluster system and avoid the single point of failure or split brain.

7.3.1. Requirements

We assume that all the Pgpool-II servers and the PostgreSQL servers are in the same subnet.

7.3.2. Cluster System Configuration

We use 3 servers with CentOS 7.4. Let these servers be server1, server2, server3. We install PostgreSQL and Pgpool-II on each server.

Figure 7-1. Cluster System Configuration

Note: The roles of Active, Standy, Primary, Standby are not fixed and may be changed by further operations.

Table 7-2. Hostname and IP address

HostnameIP AddressVirtual IP
server1192.168.137.101192.168.137.150
server2192.168.137.102
server3192.168.137.103

Table 7-3. PostgreSQL version and Configuration

ItemValueDetail
PostgreSQL Version11.1-
port5432-
$PGDATA/var/lib/pgsql/11/data-
Archive modeon/var/lib/pgsql/archivedir
Start automaticallyDisable-

Table 7-4. Pgpool-II version and Configuration

ItemValueDetail
Pgpool-II Version4.0.2-
port9999Pgpool-II accepts connections
9898PCP process accepts connections
9000watchdog accepts connections
9694UDP port for receiving Watchdog's heartbeat signal
Config file/etc/pgpool-II/pgpool.confPgpool-II config file
Pgpool-II start userrootSee Section 2.1.7 to startup Pgpool-II with non-root user
Running modestreaming replication mode-
WatchdogonLife check method: heartbeat
Start automaticallyDisable-

7.3.3. Installation

In this example, we install Pgpool-II 4.0.2 and PostgreSQL 11.1 by using RPM packages.

Install PostgreSQL by using PostgreSQL YUM repository.

# yum install https://download.postgresql.org/pub/repos/yum/11/redhat/rhel-7-x86_64/pgdg-centos11-11-2.noarch.rpm
# yum install postgresql11 postgresql11-libs postgresql11-devel postgresql11-server
      

Install Pgpool-II by using Pgpool-II YUM repository.

# yum install http://www.pgpool.net/yum/rpms/4.0/redhat/rhel-7-x86_64/pgpool-II-release-4.0-1.noarch.rpm
# yum install pgpool-II-pg11-*
      

7.3.4. Before Starting

Before you start the configuration process, please check the following prerequisites.

7.3.5. Pgpool-II Configuration

7.3.5.1. Common Settings

Here are the common settings on server1, server2 and server3.

When installing Pgpool-II from RPM, all the Pgpool-II configuration files are in /etc/pgpool-II. In this example, we copy the sample configuration file for streaming replicaton mode.

# cp /etc/pgpool-II/pgpool.conf.sample-stream /etc/pgpool-II/pgpool.conf
        

To allow Pgpool-II to accept all incoming connections, we set listen_addresses = '*'.

listen_addresses = '*'
        

Specifiy replication delay check user and password. In this example, we leave sr_check_user empty, and create the entry in pool_passwd. From Pgpool-II 4.0, if these parameters are left blank, Pgpool-II will first try to get the password for that specific user from sr_check_password file before using the empty password.

sr_check_user = 'pgpool'
sr_check_password = ''
        

Enable health check so that pgpool-II performs failover. Also, if the network is unstable, the health check fails even though the backend is running properly, failover or degenerate operation may occur. In order to prevent such incorrect detection of health check, we set health_check_max_retries = 3. Specify health_check_user and health_check_password in the same way like sr_check_user and sr_check_password.

health_check_period = 5
                                   # Health check period
                                   # Disabled (0) by default
health_check_timeout = 30
                                   # Health check timeout
                                   # 0 means no timeout
health_check_user = 'pgpool'
health_check_password = ''

health_check_max_retries = 3
        

Specify the PostgreSQL backend informations. Multiple backends can be specified by adding a number at the end of the parameter name.

# - Backend Connection Settings -

backend_hostname0 = 'server1'
                                   # Host name or IP address to connect to for backend 0
backend_port0 = 5432
                                   # Port number for backend 0
backend_weight0 = 1
                                   # Weight for backend 0 (only in load balancing mode)
backend_data_directory0 = '/var/lib/pgsql/11/data'
                                   # Data directory for backend 0
backend_flag0 = 'ALLOW_TO_FAILOVER'
                                   # Controls various backend behavior
                                   # ALLOW_TO_FAILOVER or DISALLOW_TO_FAILOVER
backend_hostname1 = 'server2'
backend_port1 = 5432
backend_weight1 = 1
backend_data_directory1 = '/var/lib/pgsql/11/data'
backend_flag1 = 'ALLOW_TO_FAILOVER'

backend_hostname2 = 'server3'
backend_port2 = 5432
backend_weight2 = 1
backend_data_directory2 = '/var/lib/pgsql/11/data'
backend_flag2 = 'ALLOW_TO_FAILOVER'
        

7.3.5.2. Failover configuration

Specify failover.sh script to be executed after failover in failover_command parameter. If we use 3 PostgreSQL servers, we need to specify follow_master_command to run after failover on the primary node failover. In case of two PostgreSQL servers, follow_master_command setting is not necessary.

failover_command = '/etc/pgpool-II/failover.sh %d %h %p %D %m %H %M %P %r %R'
follow_master_command = '/etc/pgpool-II/follow_master.sh %d %h %p %D %m %M %H %P %r %R'
      

Create /etc/pgpool-II/failover.sh, and add execute permission.

# vi /etc/pgpool-II/failover.sh
# vi /etc/pgpool-II/follow_master.sh
# chmod +x /etc/pgpool-II/{failover.sh,follow_master.sh}
      

  • /etc/pgpool-II/failover.sh

    #!/bin/bash
    # This script is run by failover_command.
    
    set -o xtrace
    exec > >(logger -i -p local1.info) 2>&1
    
    # Special values:
    #   %d = node id
    #   %h = host name
    #   %p = port number
    #   %D = database cluster path
    #   %m = new master node id
    #   %H = hostname of the new master node
    #   %M = old master node id
    #   %P = old primary node id
    #   %r = new master port number
    #   %R = new master database cluster path
    #   %% = '%' character
    
    FAILED_NODE_ID="$1"
    FAILED_NODE_HOST="$2"
    FAILED_NODE_PORT="$3"
    FAILED_NODE_PGDATA="$4"
    NEW_MASTER_NODE_ID="$5"
    NEW_MASTER_NODE_HOST="$6"
    OLD_MASTER_NODE_ID="$7"
    OLD_PRIMARY_NODE_ID="$8"
    NEW_MASTER_NODE_PORT="$9"
    NEW_MASTER_NODE_PGDATA="${10}"
    
    PGHOME=/usr/pgsql-11
    
    logger -i -p local1.info failover.sh: start: failed_node_id=$FAILED_NODE_ID old_primary_node_id=$OLD_PRIMARY_NODE_ID \
    	failed_host=$FAILED_NODE_HOST new_master_host=$NEW_MASTER_NODE_HOST
    
    # If standby node is down, skip failover.
    if [ $FAILED_NODE_ID -ne $OLD_PRIMARY_NODE_ID ]; then
        logger -i -p local1.info failover.sh: Standby node is down. Skipping failover.
        exit 0
    fi
    
    # Promote standby node.
    logger -i -p local1.info failover.sh: ssh: postgres@$NEW_MASTER_NODE_HOST pg_ctl promote
    if [ $UID -eq 0 ]; then
        su postgres -c "ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
        postgres@$NEW_MASTER_NODE_HOST ${PGHOME}/bin/pg_ctl -D ${NEW_MASTER_NODE_PGDATA} -w promote"
    else
        ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
        postgres@$NEW_MASTER_NODE_HOST ${PGHOME}/bin/pg_ctl -D ${NEW_MASTER_NODE_PGDATA} -w promote
    fi
    
    if [[ $? -ne 0 ]]; then
        logger -i -p local1.error failover.sh: new_master_host=$NEW_MASTER_NODE_HOST promote failed
        exit 1
    fi
    
    logger -i -p local1.info failover.sh: end: new_master_node_id=$NEW_MASTER_NODE_ID started as the primary node
    exit 0
              

  • /etc/pgpool-II/follow_master.sh

    #!/bin/bash
    # This script is run after failover_command to recover the slave from the new primary.
    
    set -o xtrace
    exec > >(logger -i -p local1.info) 2>&1
    
    # special values:  %d = node id
    #                  %h = host name
    #                  %p = port number
    #                  %D = database cluster path
    #                  %m = new master node id
    #                  %M = old master node id
    #                  %H = new master node host name
    #                  %P = old primary node id
    #                  %R = new master database cluster path
    #                  %r = new master port number
    #                  %% = '%' character
    FAILED_NODE_ID="$1"
    FAILED_NODE_HOST="$2"
    FAILED_NODE_PORT="$3"
    FAILED_NODE_PGDATA="$4"
    NEW_MASTER_NODE_ID="$5"
    OLD_MASTER_NODE_ID="$6"
    NEW_MASTER_NODE_HOST="$7"
    OLD_PRIMARY_NODE_ID="$8"
    NEW_MASTER_NODE_PORT="$9"
    NEW_MASTER_NODE_PGDATA="${10}"
    
    PGHOME=/usr/pgsql-11
    ARCHIVEDIR=/var/lib/pgsql/archivedir
    REPL_USER=repl
    PCP_USER=pgpool
    PGPOOL_PATH=/usr/bin
    PCP_PORT=9898
    
    
    # Recovery the slave from the new primary
    logger -i -p local1.info follow_master.sh: start: pg_basebackup for $FAILED_NODE_ID
    
    # Check the status of standby
    ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
        postgres@${FAILED_NODE_HOST} ${PGHOME}/bin/pg_ctl -w -D ${FAILED_NODE_PGDATA} status >/dev/null 2>&1
    
    # If slave is running, recover the slave from the new primary.
    if [[ $? -eq 0 ]]; then
    
        # Execute pg_basebackup at slave
        ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@${FAILED_NODE_HOST} "
            ${PGHOME}/bin/pg_ctl -w -m f -D ${FAILED_NODE_PGDATA} stop
    
            rm -rf ${FAILED_NODE_PGDATA}
            ${PGHOME}/bin/pg_basebackup -h ${NEW_MASTER_NODE_HOST} -U ${REPL_USER} -p ${NEW_MASTER_NODE_PORT} -D ${FAILED_NODE_PGDATA} -X stream -R
    
            if [[ $? -ne 0 ]]; then
                logger -i -p local1.error follow_master.sh: end: pg_basebackup failed
                exit 1
            fi
            rm -rf ${ARCHIVEDIR}/*
    cat >> ${FAILED_NODE_PGDATA}/recovery.conf << EOT
    restore_command = 'scp ${NEW_MASTER_NODE_HOST}:${ARCHIVEDIR}/%f %p'
    EOT
            $PGHOME/bin/pg_ctl -l /dev/null -w -D ${FAILED_NODE_PGDATA} start
        "
    
        if [[ $? -eq 0 ]]; then
    
            # Run pcp_attact_node to attach this slave to Pgpool-II.
            ${PGPOOL_PATH}/pcp_attach_node -w -h localhost -U ${PCP_USER} -p ${PCP_PORT} -n ${FAILED_NODE_ID}
    
            if [[ $? -ne 0 ]]; then
                logger -i -p local1.error follow_master.sh: end: pcp_attach_node failed
                exit 1
            else
                logger -i -p local1.error follow_master.sh: end: follow master failed
                exit 1
            fi
    
    else
        logger -i -p local1.info follow_master.sh: failed_nod_id=${FAILED_NODE_ID} is not running. skipping follow master command.
        exit 0
    fi
    
    logger -i -p local1.info follow_master.sh: end: follow master is finished
    exit 0
              

7.3.5.3. Pgpool-II Online Recovery Configurations

Next, in order to perform online recovery with Pgpool-II we specify the PostgreSQL user name and online recovery command recovery_1st_stage. Because Supergroup privilege of PostgreSQL is required for online recovery, we specify postgres user to recovery_user. Then, we create recovery_1st_stage and pgpool_remote_start in database cluster directory of PostgreSQL primary server (server1), and add execute permission.

recovery_user = 'postgres'
                                   # Online recovery user
recovery_password = ''
                                   # Online recovery password

recovery_1st_stage_command = 'recovery_1st_stage'
        
[server1]# su - postgres
[server1]$ vi /var/lib/pgsql/11/data/recovery_1st_stage
[server1]$ vi /var/lib/pgsql/11/data/pgpool_remote_start
[server1]$ chmod +x /var/lib/pgsql/11/data/{recovery_1st_stage,pgpool_remote_start}
        

  • /var/lib/pgsql/11/data/recovery_1st_stage

    #!/bin/bash
    # This script is run by recovery_1st_stage to recovery the slave from the primary.
    
    set -o xtrace
    exec > >(logger -i -p local1.info) 2>&1
    
    PRIMARY_NODE_PGDATA="$1"
    DEST_NODE_HOST="$2"
    DEST_NODE_PGDATA="$3"
    PRIMARY_NODE_PGPORT=$4
    
    PRIMARY_NODE_HOST=$(hostname -s)
    PGHOME=/usr/pgsql-11
    ARCHIVEDIR=/var/lib/pgsql/archivedir
    REPLUSER=repl
    
    
    logger -i -p local1.info online_recovery.sh: start: pg_basebackup for $DEST_NODE_HOST
    
    # Run pg_basebackup to recovery the slave from the primary
    ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@$DEST_NODE_HOST "
    rm -rf $DEST_NODE_PGDATA
    ${PGHOME}/bin/pg_basebackup -h $PRIMARY_NODE_HOST -U $REPLUSER -p $PRIMARY_NODE_PGPORT -D $DEST_NODE_PGDATA -X stream -R
    "
    if [[ $? -ne 0 ]]; then
        logger -i -p local1.error online_recovery.sh: end: pg_basebackup failed. online recovery failed.
        exit 1
    fi
    
    ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@$DEST_NODE_HOST "
    rm -rf $ARCHIVEDIR/*
    cat >> $DEST_NODE_PGDATA/recovery.conf << EOT
    restore_command = 'scp $PRIMARY_NODE_HOST:$archivedir/%f %p'
    EOT
    "
    
    if [[ $? -ne 0 ]]; then
        logger -i -p local1.error online_recovery.sh: end: online recovery failed
        exit 1
    else
        logger -i -p local1.info online_recovery.sh: end: online recovery is finished
        exit 0
    fi
                
  • /var/lib/pgsql/11/data/pgpool_remote_start

    #!/bin/bash
    # This script is run to start slave node after recovery.
    
    set -o xtrace
    exec > >(logger -i -p local1.info) 2>&1
    
    PGHOME=/usr/pgsql-11
    DEST_HOST="$1"
    DEST_HOST_PGDATA="$2"
    
    
    logger -i -p local1.info pgpool_remote_start: start: remote start PostgreSQL@$DEST_HOST
    
    # Start slave node
    ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@$DEST_HOST $PGHOME/bin/pg_ctl -l /dev/null -w -D $DEST_HOST_PGDATA start
    
    if [[ $? -ne 0 ]]; then
        logger -i -p local1.info  pgpool_remote_start: $DEST_HOST start failed.
        exit 1
    fi
    
    logger -i -p local1.info pgpool_remote_start: end: $DEST_HOST PostgreSQL started successfully.
              

In order to use the online recovery functionality, the functions of pgpool_recovery, pgpool_remote_start, pgpool_switch_xlog are required, so we need install pgpool_recovery on template1 of PostgreSQL server server1.

[server1]# su - postgres
[server1]$ psql template1 -c "CREATE EXTENSION pgpool_recovery"
        

7.3.5.4. Client Authentication Configuration

Because in the section Before Starting, we already set PostgreSQL authentication method to scram-sha-256, it is necessary to set a client authentication by Pgpool-II to connect to backend nodes. Please note that only AES encrypted password or clear text passowrd can be specified in health_check_password, sr_check_password, wd_lifecheck_password, recovery_password in pgpool.conf. When installing with RPM, the Pgpool-II configuration file pool_hba.conf is in /etc/pgpool-II. By default, pool_hba authentication is disabled, and set enable_pool_hba = on to enable it.

enable_pool_hba = on
        

The format of pool_hba.conf file follows very closely PostgreSQL's pg_hba.conf format. Set pgpool and postgres user's authentication method to scram-sha-256.

host    all         pgpool           0.0.0.0/0          scram-sha-256
host    all         postgres         0.0.0.0/0          scram-sha-256
        

The default password file name for authentication is pool_passwd. To use scram-sha-256 authentication, the decryption key to decrypt the passwords is required. We create the .pgpoolkey file in root user's home directory.

[all servers]# echo 'some string' > ~/.pgpoolkey 
[all servers]# chmod 600 ~/.pgpoolkey
        

Execute command pg_enc -m -k /path/to/.pgpoolkey -u username -p to regist user name and AES encrypted password in file pool_passwd. If pool_passwd doesn't exist yet, it will be created in the same directory as pgpool.conf.

[all servers]# pg_enc -m -k /root/.pgpoolkey -u pgpool -p
db password: [pgpool user's password]
[all servers]# pg_enc -m -k /root/.pgpoolkey -u postgres -p
db password: [postgres user's passowrd]

# cat /etc/pgpool-II/pool_passwd 
pgpool:AESheq2ZMZjynddMWk5sKP/Rw==
postgres:AESHs/pWL5rtXy2IwuzroHfqg==
        

7.3.5.5. Watchdog Configuration

Enable watchdog functionality on server1, server2, server3.

use_watchdog = on
        

Specify virtual IP address that accepts connections from clients on server1, server2, server3. Ensure that the IP address set to virtual IP isn't used yet.

delegate_IP = '192.168.137.150'
        

To bring up/down the virtual IP and send the ARP requests, we set if_up_cmd, if_down_cmd and arping_cmd. The network interface used in this example is "enp0s8".

if_up_cmd = 'ip addr add $_IP_$/24 dev enp0s8 label enp0s8:0'
                                    # startup delegate IP command
if_down_cmd = 'ip addr del $_IP_$/24 dev enp0s8'
                                    # shutdown delegate IP command
arping_cmd = 'arping -U $_IP_$ -w 1 -I enp0s8'
                                    # arping command
        

Set if_cmd_path and arping_path according to the command path.

if_cmd_path = '/sbin'
                                    # path to the directory where if_up/down_cmd exists
arping_path = '/usr/sbin'
                                    # arping command path
        

Specify the hostname and port number of each Pgpool-II server.

  • server1

    wd_hostname = 'server1'
    wd_port = 9000
                
  • server2

    wd_hostname = 'server2'
    wd_port = 9000
                
  • server3

    wd_hostname = 'server3'
    wd_port = 9000
                

Specify the hostname, Pgpool-II port number, and watchdog port number of monitored Pgpool-II servers on each Pgpool-II server.

  • server1

    # - Other pgpool Connection Settings -
    
    other_pgpool_hostname0 = 'server2'
                                        # Host name or IP address to connect to for other pgpool 0
                                        # (change requires restart)
    other_pgpool_port0 = 9999
                                        # Port number for other pgpool 0
                                        # (change requires restart)
    other_wd_port0 = 9000
                                        # Port number for other watchdog 0
                                        # (change requires restart)
    other_pgpool_hostname1 = 'server3'
    other_pgpool_port1 = 9999
    other_wd_port1 = 9000
                
  • server2

    # - Other pgpool Connection Settings -
    
    other_pgpool_hostname0 = 'server1'
                                        # Host name or IP address to connect to for other pgpool 0
                                        # (change requires restart)
    other_pgpool_port0 = 9999
                                        # Port number for other pgpool 0
                                        # (change requires restart)
    other_wd_port0 = 9000
                                        # Port number for other watchdog 0
                                        # (change requires restart)
    other_pgpool_hostname1 = 'server3'
    other_pgpool_port1 = 9999
    other_wd_port1 = 9000
                
  • server3

    # - Other pgpool Connection Settings -
    
    other_pgpool_hostname0 = 'server1'
                                        # Host name or IP address to connect to for other pgpool 0
                                        # (change requires restart)
    other_pgpool_port0 = 9999
                                        # Port number for other pgpool 0
                                        # (change requires restart)
    other_wd_port0 = 9000
                                        # Port number for other watchdog 0
                                        # (change requires restart)
    other_pgpool_hostname1 = 'server2'
    other_pgpool_port1 = 9999
    other_wd_port1 = 9000
                

Specify the hostname and port number of destination for sending heartbeat signal on server1, server2, server3.

  • server1

    heartbeat_destination0 = 'server2'
                                        # Host name or IP address of destination 0
                                        # for sending heartbeat signal.
                                        # (change requires restart)
    heartbeat_destination_port0 = 9694
                                        # Port number of destination 0 for sending
                                        # heartbeat signal. Usually this is the
                                        # same as wd_heartbeat_port.
                                        # (change requires restart)
    heartbeat_device0 = ''
                                        # Name of NIC device (such like 'eth0')
                                        # used for sending/receiving heartbeat
                                        # signal to/from destination 0.
                                        # This works only when this is not empty
                                        # and pgpool has root privilege.
                                        # (change requires restart)
    
    heartbeat_destination1 = 'server3'
    heartbeat_destination_port1 = 9694
    heartbeat_device1 = ''
    
                
  • server2

    heartbeat_destination0 = 'server1'
                                        # Host name or IP address of destination 0
                                        # for sending heartbeat signal.
                                        # (change requires restart)
    heartbeat_destination_port0 = 9694
                                        # Port number of destination 0 for sending
                                        # heartbeat signal. Usually this is the
                                        # same as wd_heartbeat_port.
                                        # (change requires restart)
    heartbeat_device0 = ''
                                        # Name of NIC device (such like 'eth0')
                                        # used for sending/receiving heartbeat
                                        # signal to/from destination 0.
                                        # This works only when this is not empty
                                        # and pgpool has root privilege.
                                        # (change requires restart)
    
    heartbeat_destination1 = 'server3'
    heartbeat_destination_port1 = 9694
    heartbeat_device1 = ''
    
                
  • server3

    heartbeat_destination0 = 'server1'
                                        # Host name or IP address of destination 0
                                        # for sending heartbeat signal.
                                        # (change requires restart)
    heartbeat_destination_port0 = 9694
                                        # Port number of destination 0 for sending
                                        # heartbeat signal. Usually this is the
                                        # same as wd_heartbeat_port.
                                        # (change requires restart)
    heartbeat_device0 = ''
                                        # Name of NIC device (such like 'eth0')
                                        # used for sending/receiving heartbeat
                                        # signal to/from destination 0.
                                        # This works only when this is not empty
                                        # and pgpool has root privilege.
                                        # (change requires restart)
    
    heartbeat_destination1 = 'server2'
    heartbeat_destination_port1 = 9694
    heartbeat_device1 = ''
                

7.3.5.6. /etc/sysconfig/pgpool Configuration

If you want to ignore the pgpool_status file at startup of Pgpool-II, add "- D" to the start option OPTS to /etc/sysconfig/pgpool.

[all servers]# vi /etc/sysconfig/pgpool 
...
OPTS=" -D -n"
        

7.3.5.7. Logging

In the example, we output Pgpool-II's log to syslog.

log_destination = 'syslog'
                                   # Where to log
                                   # Valid values are combinations of stderr,
                                   # and syslog. Default to stderr.

syslog_facility = 'LOCAL1'
                                   # Syslog local facility. Default to LOCAL0
        

Create Pgpool-II log file.

[all servers]# mkdir /var/log/pgpool-II
[all servers]# touch /var/log/pgpool-II/pgpool.log
        

Edit config file of syslog /etc/rsyslog.conf.

[all servers]# vi /etc/rsyslog.conf
...
*.info;mail.none;authpriv.none;cron.none;LOCAL1.none    /var/log/messages
LOCAL1.*                                                /var/log/pgpool-II/pgpool.log
        

Setting logrotate same as /var/log/messages.

[all servers]# vi /etc/logrotate.d/syslog
...
/var/log/messages
/var/log/pgpool-II/pgpool.log
/var/log/secure
        

Restart rsyslog service.

[all servers]# systemctl restart rsyslog
        

7.3.5.8. PCP Command Configuration

Since user authentication is required to use the PCP command, specify user name and md5 encrypted password in pcp.conf. Here we create the encrypted password for pgpool user, and add "username:encrypted password" in /etc/pgpool-II/pcp.conf.

[all servers]# echo 'pgpool:'`pg_md5 PCP passowrd` >> /etc/pgpool-II/pcp.conf
        

7.3.5.9. .pcppass

Since follow_master_command script has to execute PCP command without entering the password, we create .pcppass in the home directory of Pgpool-II startup user (root user).

[all servers]# echo 'localhost:9898:pgpool:pgpool' > ~/.pcppass
[all servers]# chmod 600 ~/.pcppass
        

The settings of Pgpool-II is completed.

7.3.6. Starting/Stopping Pgpool-II

Next we start Pgpool-II. Before starting Pgpool-II, please start PostgreSQL servers first. Also, when stopping PostgreSQL, it is necessary to stop Pgpool-II first.

7.3.7. How to use

Let's start to use Pgpool-II. First, let's start Pgpool-II on server1, server2, server3 by using the following command.

# systemctl start pgpool.service
      

7.3.7.1. Set up PostgreSQL standby server

First, we should set up PostgreSQL standby server by using Pgpool-II online recovery functionality. Ensure that recovery_1st_stage and pgpool_remote_start scripts used by pcp_recovery_node command are in database cluster directory of PostgreSQL primary server (server1).

# pcp_recovery_node -h 192.168.137.150 -p 9898 -U pgpool -n 1
Password: 
pcp_recovery_node -- Command Successful

# pcp_recovery_node -h 192.168.137.150 -p 9898 -U pgpool -n 2
Password: 
pcp_recovery_node -- Command Successful
      

After executing pcp_recovery_node command, vertify that server2 and server3 are started as PostgreSQL standby server.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
 node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+---------------------
 0       | server1  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 | 2019-02-18 11:26:31
 1       | server2  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | 2019-02-18 11:27:49
 2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | 2019-02-18 11:27:49
      

7.3.7.2. Switching active/standby watchdog

Confirm the watchdog status by using pcp_watchdog_info. The Pgpool-II server which is started first run as MASTER.

# pcp_watchdog_info -h 192.168.137.150 -p 9898 -U pgpool
Password: 
3 YES server1:9999 Linux server1 server1

server1:9999 Linux server1 server1 9999 9000 4 MASTER  #The Pgpool-II server started first becames "MASTER".
server2:9999 Linux server2 server2 9999 9000 7 STANDBY #run as standby
server3:9999 Linux server3 server3 9999 9000 7 STANDBY #run as standby
        

Stop active server server1, then server2 or server3 will be promoted to active server. To stop server1, we can stop Pgpool-II service or shutdown the whole system. Here, we stop Pgpool-II service.

[server1]# systemctl stop pgpool.service

# pcp_watchdog_info -p 9898 -h 192.168.137.150 -U pgpool
Password: 
3 YES server2:9999 Linux server2 server2

server2:9999 Linux server2 server2 9999 9000 4 MASTER     #server2 is promoted to MASTER
server1:9999 Linux server1 server1 9999 9000 10 SHUTDOWN  #server1 is stopped
server3:9999 Linux server3 server3 9999 9000 7 STANDBY    #server3 runs as STANDBY
        

Start Pgpool-II (server1) which we have stopped again, and vertify that server1 runs as a standby.

[server1]# systemctl start pgpool.service

[server1]# pcp_watchdog_info -p 9898 -h 192.168.137.150 -U pgpool
Password: 
3 YES server2:9999 Linux server2 server2

server2:9999 Linux server2 server2 9999 9000 4 MASTER
server1:9999 Linux server1 server1 9999 9000 7 STANDBY
server3:9999 Linux server3 server3 9999 9000 7 STANDBY
        

7.3.7.3. Failover

First, use psql to connect to PostgreSQL via virtual IP, and verify the backend informations.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
 node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+---------------------
 0       | server1  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 | 2019-02-18 13:08:02
 1       | server2  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | 2019-02-18 13:21:56
 2       | server3  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | 2019-02-18 13:21:56
        

Next, stop primary PostgreSQL server server1, and verify automatic failover.

[server1]$ pg_ctl -D /var/lib/pgsql/11/data -m immediate stop
        

After stopping PostgreSQL on server1, failover occurs and PostgreSQL on server2 becomes new primary DB.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
 node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+---------------------
 0       | server1  | 5432 | down   | 0.333333  | standby | 0          | false             | 0                 | 2019-02-18 13:22:25
 1       | server2  | 5432 | up     | 0.333333  | primary | 0          | true              | 0                 | 2019-02-18 13:22:25
 2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | 2019-02-18 13:22:28
        

server3 is running as standby of new primary server2.

[server3]# psql -h server3 -p 5432 -U pgpool postgres -c "select pg_is_in_recovery()"
 pg_is_in_recovery 
-------------------
 t

[server2]# su - postgres
$ psql
postgres=# select pg_is_in_recovery();
 pg_is_in_recovery 
-------------------
 f

postgres=# select * from pg_stat_replication;
-[ RECORD 1 ]----+------------------------------
pid              | 11915
usesysid         | 16385
usename          | repl
application_name | walreceiver
client_addr      | 192.168.137.103
client_hostname  | 
client_port      | 37834
backend_start    | 2019-02-18 13:22:27.472038+09
backend_xmin     | 
state            | streaming
sent_lsn         | 0/8E000060
write_lsn        | 0/8E000060
flush_lsn        | 0/8E000060
replay_lsn       | 0/8E000060
write_lag        | 
flush_lag        | 
replay_lag       | 
sync_priority    | 0
sync_state       | async
        

7.3.7.4. Online Recovery

Here, we use Pgpool-II online recovery functionality to restore server1 (old primary server) as a standby. Before restoring the old primary server, please ensure that recovery_1st_stage and pgpool_remote_start scripts exist in database cluster directory of current primary server server2.

# pcp_recovery_node -h 192.168.137.150 -p 9898 -U pgpool -n 0
Password: 
pcp_recovery_node -- Command Successful
        

Then verify that server1 is started as a standby.

# psql -h 192.168.137.150 -p 9999 -U pgpool postgres -c "show pool_nodes"
 node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | last_status_change  
---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+---------------------
 0       | server1  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | 2019-02-18 13:27:44
 1       | server2  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 | 2019-02-18 13:22:25
 2       | server3  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | 2019-02-18 13:22:28