Ygthkb

I am new to Postgresql and Pgpool II setup. I have configured the Postgresql HA/Load balancing using Pgpool II and Repmgr.

I have followed the link to do the setup.

The setup consist of 3 nodes and verison of Application and OS is as mentioned below:
OS version => CentOS 6.8 (On all the 3 nodes)

Pgpool node => 192.168.0.4
Postgresql Nodes:
node1 (Master in read-write mode) => 192.168.0.6
node2 (Standby node in read only mode) => 192.168.0.7

Pgpool II version => pgpool-II version 3.5.0 (ekieboshi).
Postgresql Version => PostgreSQL 9.4.8
Repmgr Version => repmgr 3.1.3 (PostgreSQL 9.4.8)

I have configured the Pgpool in Master-Slave mode using Streaming replication.

The setup is as shown in the below image:

When I bring down the Master node(192.168.0.6), the automatic failover happens successfully and the Slave node(192.168.0.7) becomes the new Master node.

After failover, I have to recover the failed node(192.168.0.6) manually and sync it with the new Master node. Then register the node(192.168.0.6) as a new Standby node.

I want to automate the Recovery process of the failed node and add it to the cluster back.

The pgpool.conf file on the Pgpool node(192.168.0.4) contains parameter recovery_1st_stage_command. I have set the parameter recovery_1st_stage_command = 'basebackup.sh'. I have placed the script 'basebackup.sh' file on both the Postgresql nodes(192.168.0.6, 192.168.0.7) under the data directory '/var/lib/pgsql/9.4/data'. Also I have placed the script 'pgpool_remote_start' on both the Postgresql nodes(192.168.0.6, 192.168.0.7) under the directory '/var/lib/pgsql/9.4/data'.

Also created the pgpool extension "pgpool_recovery and pgpool_adm" on both the database node.

After the failover is completed, the 'basebackup.sh' is not executed automatically. I have to run the command 'pcp_recovey_node' manually on the Pgpool node(192.168.0.4) to recover the failed node(192.168.0.6).

How can I automate the execution of pcp_recovery_node command on the Pgpool node with out any manual intervention.

Scripts used by me as follows:

basebackup.sh script

#!/bin/bash

# first stage recovery

# $1 datadir

# $2 desthost

# $3 destdir



#as I'm using repmgr it's not necessary for me to know datadir(master) $1

RECOVERY_NODE=$2

CLUSTER_PATH=$3

#repmgr needs to know the master's ip

MASTERNODE=`/sbin/ifconfig eth0 | grep inet | awk '{print $2}' | sed 's/addr://'`



cmd1=`ssh postgres@$RECOVERY_NODE "repmgr -D $CLUSTER_PATH --force standby clone $MASTERNODE"`

echo $cmd1

pgpool_remote_start script

#! /bin/sh



if [ $# -ne 2 ]

then

    echo "pgpool_remote_start remote_host remote_datadir"

    exit 1

fi



DEST=$1

DESTDIR=$2

PGCTL=/usr/pgsql-9.4/bin/pg_ctl



ssh -T $DEST $PGCTL -w -D $DESTDIR start 2>/dev/null 1>/dev/null < /dev/null &  

failover.sh script

#!/bin/sh

failed_node=$1

new_master=$2

(

date

echo "Failed node: $failed_node"

set -x



# Promote standby/slave to be a new master (old master failed)

/usr/bin/ssh -T -l postgres $new_master "/usr/pgsql-9.4/bin/repmgr -f /var/lib/pgsql/repmgr/repmgr.conf standby promote 2>/dev/null 1>/dev/null <&-"

exit 0;

) 2>&1 | tee -a /tmp/pgpool_failover.log

Help me with the procedure to automate the recovery of the failed node.

Also let me know, for failover is it compulsory to use repmgr or we can do it without repmgr. Also specify any other method for failover without using Repmgr, its advantages and disadvantages over Repmgr.

It is as designed: when pgpool does the failover, the failed master is ejected from the pool so that there is a protection against a split-brain. If the failed master comes back again (degenrated master), pgpool will not automatically perform the recovery operation. You have to manually execute the command pcp_recovery_node command.

If you want to automate this, then you can have a cron job running on each database, this cron would check the status of the database and when it detects a degenerated master it would execute the pcp_recovery_node command. This script can also take care of re-attaching failed standby databases (when a standby fails, pgpool ejects it from the pool and it does not re-attach it when the standby comes back).

I did something like that, it is a bit tricky, you must make sure that the script is never executed twice, for example if the cron interval is shorted than the time to perform the recovery (have a mechanism of a pid file to protect agains that). Otherwise it works.

As for repmgr, I use their scripts to perform failover, recovery, etc. but I don't use repmgrd to automate the failover, I found it safer to have the automatic failover done by pgpool.