7.3. Pgpool-II + Watchdog Setup Example

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 replication 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 = '*'
     

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

# - Backend Connection Settings -

backend_hostname0 = 'server1'
backend_port0 = 5432
backend_weight0 = 1
backend_data_directory0 = '/var/lib/pgsql/11/data'
backend_flag0 = 'ALLOW_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 %H %M %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 there's no master node anymore, skip failover.
  if [ $NEW_MASTER_NODE_ID -lt 0 ]; then
      logger -i -p local1.info failover.sh: All nodes are down. Skipping failover.
      exit 0
  fi
  
  ## Test passwrodless SSH
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@${NEW_MASTER_NODE_HOST} -i ~/.ssh/id_rsa_pgpool ls /tmp > /dev/null
  
  if [ $? -ne 0 ]; then
      logger -i -p local1.error failover.sh: passwrodless SSH to postgres@${NEW_MASTER_NODE_HOST} failed. Please setup passwrodless SSH.
      exit 1
  fi
  
  # 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: Primary node is down, promote standby node PostgreSQL@${NEW_MASTER_NODE_HOST}.
  
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
  postgres@${NEW_MASTER_NODE_HOST} -i ~/.ssh/id_rsa_pgpool ${PGHOME}/bin/pg_ctl -D ${NEW_MASTER_NODE_PGDATA} -w promote
  
  
  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 synchronize the Standby with 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
  #                  %H = new master node host name
  #                  %M = old master node id
  #                  %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"
  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
  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: synchronize the Standby node PostgreSQL@${FAILED_NODE_HOST} with the new Primary node PostgreSQL@${NEW_MASTER_NODE_HOST}
  
  ## Test passwrodless SSH
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@${NEW_MASTER_NODE_HOST} -i ~/.ssh/id_rsa_pgpool ls /tmp > /dev/null
  
  if [ $? -ne 0 ]; then
      logger -i -p local1.error follow_master.sh: passwrodless SSH to postgres@${NEW_MASTER_NODE_HOST} failed. Please setup passwrodless SSH.
      exit 1
  fi
  
  ## Get PostgreSQL major version
  PGVERSION=`${PGHOME}/bin/initdb -V | awk '{print $3}' | sed 's/\..*//' | sed 's/\([0-9]*\)[a-zA-Z].*/\1/'`
  
  if [ ${PGVERSION} -ge 12 ]; then
      RECOVERYCONF=${FAILED_NODE_PGDATA}/myrecovery.conf
  else
      RECOVERYCONF=${FAILED_NODE_PGDATA}/recovery.conf
  fi
  
  # Check the status of standby
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
      postgres@${FAILED_NODE_HOST} -i ~/.ssh/id_rsa_pgpool ${PGHOME}/bin/pg_ctl -w -D ${FAILED_NODE_PGDATA} status
  
  ## If Standby is running, run pg_basebackup.
  if [ $? -eq 0 ]; then
  
      # Execute pg_basebackup
      ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@${FAILED_NODE_HOST} -i ~/.ssh/id_rsa_pgpool "
  
          set -o errexit
          ${PGHOME}/bin/pg_ctl -w -m f -D ${FAILED_NODE_PGDATA} stop
  
          rm -rf ${FAILED_NODE_PGDATA}
          rm -rf ${ARCHIVEDIR}/*
  
          ${PGHOME}/bin/pg_basebackup -h ${NEW_MASTER_NODE_HOST} -U ${REPL_USER} -p ${NEW_MASTER_NODE_PORT} -D ${FAILED_NODE_PGDATA} -X stream
  
          if [ ${PGVERSION} -ge 12 ]; then
              sed -i -e \"\\\$ainclude_if_exists = '$(echo ${RECOVERYCONF} | sed -e 's/\//\\\//g')'\" \
                     -e \"/^include_if_exists = '$(echo ${RECOVERYCONF} | sed -e 's/\//\\\//g')'/d\" ${FAILED_NODE_PGDATA}/postgresql.conf
          fi
        
          cat > ${RECOVERYCONF} << EOT
  primary_conninfo = 'host=${NEW_MASTER_NODE_HOST} port=${NEW_MASTER_NODE_PORT} user=${REPL_USER} passfile=''/var/lib/pgsql/.pgpass'''
  recovery_target_timeline = 'latest'
  restore_command = 'scp ${NEW_MASTER_NODE_HOST}:${ARCHIVEDIR}/%f %p'
  EOT
  
          if [ ${PGVERSION} -ge 12 ]; then
              touch ${FAILED_NODE_PGDATA}/standby.signal
          else
              echo \"standby_mode = 'on'\" >> ${RECOVERYCONF}
          fi
      "
  
      if [ $? -ne 0 ]; then
          logger -i -p local1.error follow_master.sh: end: pg_basebackup failed
          exit 1
      fi
  
      # start Standby node on ${FAILED_NODE_HOST}
      ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null \
              postgres@${FAILED_NODE_HOST} -i ~/.ssh/id_rsa_pgpool $PGHOME/bin/pg_ctl -l /dev/null -w -D ${FAILED_NODE_PGDATA} start
  
      # If start Standby successfully, attach this node
      if [ $? -eq 0 ]; then
  
          # Run pcp_attact_node to attach Standby node 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
          fi
  
      # If start Standby failed, drop replication slot "${FAILED_NODE_HOST}"
      else
          logger -i -p local1.error follow_master.sh: end: follow master command 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 command complete
  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'
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 executed by "recovery_1st_stage" to recovery a Standby node.
  
  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_PORT="$4"
  DEST_NODE_PORT=5432
  
  PRIMARY_NODE_HOST=$(hostname)
  PGHOME=/usr/pgsql-11
  ARCHIVEDIR=/var/lib/pgsql/archivedir
  REPL_USER=repl
  
  logger -i -p local1.info recovery_1st_stage: start: pg_basebackup for Standby node PostgreSQL@{$DEST_NODE_HOST}
  
  ## Test passwrodless SSH
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@${DEST_NODE_HOST} -i ~/.ssh/id_rsa_pgpool ls /tmp > /dev/null
  
  if [ $? -ne 0 ]; then
      logger -i -p local1.error recovery_1st_stage: passwrodless SSH to postgres@${DEST_NODE_HOST} failed. Please setup passwrodless SSH.
      exit 1
  fi
  
  ## Get PostgreSQL major version
  PGVERSION=`${PGHOME}/bin/initdb -V | awk '{print $3}' | sed 's/\..*//' | sed 's/\([0-9]*\)[a-zA-Z].*/\1/'`
  if [ $PGVERSION -ge 12 ]; then
      RECOVERYCONF=${DEST_NODE_PGDATA}/myrecovery.conf
  else
      RECOVERYCONF=${DEST_NODE_PGDATA}/recovery.conf
  fi
  
  ## Execute pg_basebackup to recovery Standby node
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@$DEST_NODE_HOST -i ~/.ssh/id_rsa_pgpool "
  
      set -o errexit
  
      rm -rf $DEST_NODE_PGDATA
      rm -rf $ARCHIVEDIR/*
  
      ${PGHOME}/bin/pg_basebackup -h ${PRIMARY_NODE_HOST} -U ${REPL_USER} -p ${PRIMARY_NODE_PORT} -D ${DEST_NODE_PGDATA} -X stream
  
      if [ ${PGVERSION} -ge 12 ]; then
          sed -i -e \"\\\$ainclude_if_exists = '$(echo ${RECOVERYCONF} | sed -e 's/\//\\\//g')'\" \
                 -e \"/^include_if_exists = '$(echo ${RECOVERYCONF} | sed -e 's/\//\\\//g')'/d\" ${DEST_NODE_PGDATA}/postgresql.conf
      fi
  
      cat > ${RECOVERYCONF} << EOT
  primary_conninfo = 'host=${PRIMARY_NODE_HOST} port=${PRIMARY_NODE_PORT} user=${REPL_USER} passfile=''/var/lib/pgsql/.pgpass'''
  recovery_target_timeline = 'latest'
  restore_command = 'scp ${PRIMARY_NODE_HOST}:${ARCHIVEDIR}/%f %p'
  EOT
  
      if [ ${PGVERSION} -ge 12 ]; then
          touch ${DEST_NODE_PGDATA}/standby.signal
      else
          echo \"standby_mode = 'on'\" >> ${RECOVERYCONF}
      fi
  
      sed -i \"s/#*port = .*/port = ${DEST_NODE_PORT}/\" ${DEST_NODE_PGDATA}/postgresql.conf
  "
  
  if [ $? -ne 0 ]; then
      logger -i -p local1.error recovery_1st_stage: end: pg_basebackup failed. online recovery failed
      exit 1
  fi
  
  logger -i -p local1.info recovery_1st_stage: end: recovery_1st_stage complete
  exit 0
         

• /var/lib/pgsql/11/data/pgpool_remote_start

  #!/bin/bash
  # This script is run after recovery_1st_stage to start Standby node.
  
  set -o xtrace
  exec > >(logger -i -p local1.info) 2>&1
  
  PGHOME=/usr/pgsql-11
  DEST_NODE_HOST="$1"
  DEST_NODE_PGDATA="$2"
  
  
  logger -i -p local1.info pgpool_remote_start: start: remote start Standby node PostgreSQL@$DEST_NODE_HOST
  
  ## Test passwrodless SSH
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@${DEST_NODE_HOST} -i ~/.ssh/id_rsa_pgpool ls /tmp > /dev/null
  
  if [ $? -ne 0 ]; then
      logger -i -p local1.error pgpool_remote_start: passwrodless SSH to postgres@${DEST_NODE_HOST} failed. Please setup passwrodless SSH.
      exit 1
  fi
  
  ## Start Standby node
  ssh -T -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null postgres@$DEST_NODE_HOST -i ~/.ssh/id_rsa_pgpool "
      $PGHOME/bin/pg_ctl -l /dev/null -w -D $DEST_NODE_PGDATA start
  "
  
  if [ $? -ne 0 ]; then
      logger -i -p local1.error pgpool_remote_start: PostgreSQL@$DEST_NODE_HOST start failed.
      exit 1
  fi
  
  logger -i -p local1.info pgpool_remote_start: end: PostgreSQL@$DEST_NODE_HOST started successfully.
  exit 0
         

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 password 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 register 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'
if_down_cmd = 'ip addr del $_IP_$/24 dev enp0s8'
arping_cmd = 'arping -U $_IP_$ -w 1 -I enp0s8'
     

Set if_cmd_path and arping_path according to the command path.

if_cmd_path = '/sbin'
arping_path = '/usr/sbin'
     

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'
  other_pgpool_port0 = 9999
  other_wd_port0 = 9000
  
  other_pgpool_hostname1 = 'server3'
  other_pgpool_port1 = 9999
  other_wd_port1 = 9000
         

• server2

  # - Other pgpool Connection Settings -
  
  other_pgpool_hostname0 = 'server1'
  other_pgpool_port0 = 9999
  other_wd_port0 = 9000
  
  other_pgpool_hostname1 = 'server3'
  other_pgpool_port1 = 9999
  other_wd_port1 = 9000
         

• server3

  # - Other pgpool Connection Settings -
  
  other_pgpool_hostname0 = 'server1'
  other_pgpool_port0 = 9999
  other_wd_port0 = 9000
  
  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'
  heartbeat_destination_port0 = 9694
  heartbeat_device0 = ''
  
  heartbeat_destination1 = 'server3'
  heartbeat_destination_port1 = 9694
  heartbeat_device1 = ''
  
         

• server2

  heartbeat_destination0 = 'server1'
  heartbeat_destination_port0 = 9694
  heartbeat_device0 = ''
  
  heartbeat_destination1 = 'server3'
  heartbeat_destination_port1 = 9694
  heartbeat_device1 = ''
  
         

• server3

  heartbeat_destination0 = 'server1'
  heartbeat_destination_port0 = 9694
  heartbeat_device0 = ''
  
  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'
syslog_facility = 'LOCAL1'
     

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.

7.3.7.1. 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, verify 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 verify 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 information.

# 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