Pgpool-II + Watchdog Setup Example

8.3.5.1. 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 -p /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'
                                            # 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'
   

To show "replication_state" and "replication_sync_state" column in SHOW POOL NODES command result, backend_application_name parameter is required. Here we specify each backend's hostname in these parameters. ( Pgpool-II 4.1 or later)

    ...
    backend_application_name0 = 'server1'
    ...
    backend_application_name1 = 'server2'
    ...
    backend_application_name2 = 'server3'
   

8.3.5.2. 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.

Pgpool-II replaces the following special characters with the backend specific information while executing the scripts. See failover_command for more details about each character.

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

Sample scripts failover.sh and follow_master.sh are installed in /etc/pgpool-II/ . Create failover scripts using these sample files.

    # cp /etc/pgpool-II/failover.sh{.sample,}
    # cp /etc/pgpool-II/follow_master.sh{.sample,}
   

Basically, it should work if you change PGHOME according to PostgreSQL installation directory.

    [server1]# vi /etc/pgpool-II/failover.sh
    ...
    PGHOME=/usr/pgsql-11
    ...

    [server1]# vi /etc/pgpool-II/follow_master.sh
    ...
    PGHOME=/usr/pgsql-11
    ...
   

8.3.5.3. 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 Superuser privilege in PostgreSQL is required for performing online recovery, we specify postgres user in 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'
   

Online recovery sample scripts recovery_1st_stage and pgpool_remote_start are installed in /etc/pgpool-II/ . Copy these files to the data directory of the primary server (server1).

    [server1]# cp /etc/pgpool-II/recovery_1st_stage.sample /var/lib/pgsql/11/data/
    [server1]# cp /etc/pgpool-II/pgpool_remote_start.sample /var/lib/pgsql/11/data/
    [server1]# chown postgres:postgres /var/lib/pgsql/11/data/{recovery_1st_stage,pgpool_remote_start}
   

Basically, it should work if you change PGHOME according to PostgreSQL installation directory.

    [server1]# vi /var/lib/pgsql/11/data/recovery_1st_stage
    ...
    PGHOME=/usr/pgsql-11
    ...

    [server1]# vi /var/lib/pgsql/11/data/pgpool_remote_start
    ...
    PGHOME=/usr/pgsql-11
    ...
   

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"
   

8.3.5.4. 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. When installing with RPM, the Pgpool-II configuration file pool_hba.conf is in /etc/pgpool-II . By default, pool_hba authentication is disabled, 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 Pgpool-II start user postgres 's ( Pgpool-II 4.1 or later) home directory. ( Pgpool-II 4.0 or before, by default Pgpool-II is started as root )

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

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

8.3.5.5. 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". Since root privilege is required to execute if_up/down_cmd or arping_cmd command, use setuid on these command or allow Pgpool-II startup user, postgres user (Pgpool-II 4.1 or later) to run sudo command without a password. If installed from RPM, the postgres user has been configured to run ip/arping via sudo without a password.

if_up_cmd = '/usr/bin/sudo /sbin/ip addr add $_IP_$/24 dev enp0s8 label enp0s8:0'
if_down_cmd = '/usr/bin/sudo /sbin/ip addr del $_IP_$/24 dev enp0s8'
arping_cmd = '/usr/bin/sudo /usr/sbin/arping -U $_IP_$ -w 1 -I enp0s8'
   

Set if_cmd_path and arping_path according to the command path. If if_up/down_cmd or arping_cmd starts with "/", these parameters will be ignored.

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'
                                              # 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 = ''
       

8.3.5.6. /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"
   

8.3.5.7. 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
   

8.3.5.8. 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
   

8.3.5.9. .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.

   # systemctl start pgpool.service
  

8.3.7.1. 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"
    Password for user pgpool
    node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
    ---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
    0       | server1  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 |                   |                        | 2019-08-06 11:13:17
    1       | server2  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | streaming         | async                  | 2019-08-06 11:13:25
    2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:14:20
    (3 rows)
   

8.3.7.2. 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
   

8.3.7.3. 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"
    Password for user pgpool:
    node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
    ---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
    0       | server1  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 |                   |                        | 2019-08-06 11:13:17
    1       | server2  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | streaming         | async                  | 2019-08-06 11:13:25
    2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:14:20
    (3 rows)
   

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"
    Password for user pgpool:
    node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
    ---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
    0       | server1  | 5432 | down   | 0.333333  | standby | 0          | false             | 0                 |                   |                        | 2019-08-06 11:36:03
    1       | server2  | 5432 | up     | 0.333333  | primary | 0          | true              | 0                 |                   |                        | 2019-08-06 11:36:03
    2       | server3  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:36:15
    (3 rows)
   

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]# psql -h server2 -p 5432 -U pgpool postgres -c "select pg_is_in_recovery()"
    pg_is_in_recovery 
    -------------------
    f

    [server2]# psql -h server2 -p 5432 -U pgpool postgres -c "select * from pg_stat_replication" -x
    -[ RECORD 1 ]----+------------------------------
    pid              | 11059
    usesysid         | 16392
    usename          | repl
    application_name | server3
    client_addr      | 192.168.137.103
    client_hostname  | 
    client_port      | 48694
    backend_start    | 2019-08-06 11:36:07.479161+09
    backend_xmin     | 
    state            | streaming
    sent_lsn         | 0/75000148
    write_lsn        | 0/75000148
    flush_lsn        | 0/75000148
    replay_lsn       | 0/75000148
    write_lag        | 
    flush_lag        | 
    replay_lag       | 
    sync_priority    | 0
    sync_state       | async
    reply_time       | 2019-08-06 11:42:59.823961+09
   

8.3.7.4. 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"
    Password for user pgpool:
    node_id | hostname | port | status | lb_weight |  role   | select_cnt | load_balance_node | replication_delay | replication_state | replication_sync_state | last_status_change  
    ---------+----------+------+--------+-----------+---------+------------+-------------------+-------------------+-------------------+------------------------+---------------------
    0       | server1  | 5432 | up     | 0.333333  | standby | 0          | false             | 0                 | streaming         | async                  | 2019-08-06 11:48:05
    1       | server2  | 5432 | up     | 0.333333  | primary | 0          | false             | 0                 |                   |                        | 2019-08-06 11:36:03
    2       | server3  | 5432 | up     | 0.333333  | standby | 0          | true              | 0                 | streaming         | async                  | 2019-08-06 11:36:15
    (3 rows)