| pgpool-II 4.0.20 Documentation | |||
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This tutorial explains the simple way to try "Watchdog". What you need is 2 Linux boxes on which Pgpool-II is installed and a PostgreSQL on the same machine or in the other one. It is enough that 1 node for backend exists. You can use watchdog with Pgpool-II in any mode: replication mode, master/slave mode and raw mode.
This example uses use "osspc16" as an Active node and "osspc20" as a Standby node. "Someserver" means one of them.
Set the following parameters in both of active and standby nodes.
First of all, set use_watchdog to on.
use_watchdog = on
# Activates watchdog
Specify the up stream servers (e.g. application servers). Leaving it blank is also fine.
trusted_servers = ''
# trusted server list which are used
# to confirm network connection
# (hostA,hostB,hostC,...)
Specify the TCP port number for watchdog communication.
wd_port = 9000
# port number for watchdog service
Specify the IP address to be used as a virtual IP address in the delegate_IP.
delegate_IP = '133.137.177.143'
# delegate IP address
Note: Make sure the IP address configured as a Virtual IP should be free and is not used by any other machine.
Next, set the following parameters for each Pgpool-II. Specify other_pgpool_hostname, other_pgpool_port and other_wd_port with the values of other Pgpool-II server values.
other_pgpool_hostname0 = 'osspc20'
# Host name or IP address to connect to for other pgpool 0
other_pgpool_port0 = 9999
# Port number for other pgpool 0
other_wd_port0 = 9000
# Port number for other watchdog 0
other_pgpool_hostname0 = 'osspc16'
# Host name or IP address to connect to for other pgpool 0
other_pgpool_port0 = 9999
# Port number for other pgpool 0
other_wd_port0 = 9000
# Port number for other watchdog 0
Start Pgpool-II on each servers from root user with "-n" switch and redirect log messages into pgpool.log file.
First start the Pgpool-II on Active server.
[user@osspc16]$ su -
[root@osspc16]# {installed_dir}/bin/pgpool -n -f {installed_dir}/etc/pgpool.conf > pgpool.log 2>&1
Log messages will show that Pgpool-II has the virtual IP address and starts watchdog process.
LOG: I am announcing my self as master/coordinator watchdog node
LOG: I am the cluster leader node
DETAIL: our declare coordinator message is accepted by all nodes
LOG: I am the cluster leader node. Starting escalation process
LOG: escalation process started with PID:59449
LOG: watchdog process is initialized
LOG: watchdog: escalation started
LOG: I am the master watchdog node
DETAIL: using the local backend node status
Now start the Pgpool-II on Standby server.
[user@osspc20]$ su -
[root@osspc20]# {installed_dir}/bin/pgpool -n -f {installed_dir}/etc/pgpool.conf > pgpool.log 2>&1
Log messages will show that Pgpool-II has joined the watchdog cluster as standby watchdog.
LOG: watchdog cluster configured with 1 remote nodes
LOG: watchdog remote node:0 on Linux_osspc16_9000:9000
LOG: interface monitoring is disabled in watchdog
LOG: IPC socket path: "/tmp/.s.PGPOOLWD_CMD.9000"
LOG: watchdog node state changed from [DEAD] to [LOADING]
LOG: new outbound connection to Linux_osspc16_9000:9000
LOG: watchdog node state changed from [LOADING] to [INITIALIZING]
LOG: watchdog node state changed from [INITIALIZING] to [STANDBY]
LOG: successfully joined the watchdog cluster as standby node
DETAIL: our join coordinator request is accepted by cluster leader node "Linux_osspc16_9000"
LOG: watchdog process is initialized
Confirm to ping to the virtual IP address.
[user@someserver]$ ping 133.137.177.142
PING 133.137.177.143 (133.137.177.143) 56(84) bytes of data.
64 bytes from 133.137.177.143: icmp_seq=1 ttl=64 time=0.328 ms
64 bytes from 133.137.177.143: icmp_seq=2 ttl=64 time=0.264 ms
64 bytes from 133.137.177.143: icmp_seq=3 ttl=64 time=0.412 ms
Confirm if the Active server which started at first has the virtual IP address.
[root@osspc16]# ifconfig
eth0 ...
eth0:0 inet addr:133.137.177.143 ...
lo ...
Confirm if the Standby server which started not at first doesn't have the virtual IP address.
[root@osspc20]# ifconfig
eth0 ...
lo ...
Try to connect PostgreSQL by "psql -h delegate_IP -p port".
[user@someserver]$ psql -h 133.137.177.142 -p 9999 -l
Confirm how the Standby server works when the Active server can't provide its service. Stop Pgpool-II on the Active server.
[root@osspc16]# {installed_dir}/bin/pgpool stop
Then, the Standby server starts to use the virtual IP address. Log shows:
LOG: remote node "Linux_osspc16_9000" is shutting down
LOG: watchdog cluster has lost the coordinator node
LOG: watchdog node state changed from [STANDBY] to [JOINING]
LOG: watchdog node state changed from [JOINING] to [INITIALIZING]
LOG: I am the only alive node in the watchdog cluster
HINT: skipping stand for coordinator state
LOG: watchdog node state changed from [INITIALIZING] to [MASTER]
LOG: I am announcing my self as master/coordinator watchdog node
LOG: I am the cluster leader node
DETAIL: our declare coordinator message is accepted by all nodes
LOG: I am the cluster leader node. Starting escalation process
LOG: watchdog: escalation started
LOG: watchdog escalation process with pid: 59551 exit with SUCCESS.
Confirm to ping to the virtual IP address.
[user@someserver]$ ping 133.137.177.142
PING 133.137.177.143 (133.137.177.143) 56(84) bytes of data.
64 bytes from 133.137.177.143: icmp_seq=1 ttl=64 time=0.328 ms
64 bytes from 133.137.177.143: icmp_seq=2 ttl=64 time=0.264 ms
64 bytes from 133.137.177.143: icmp_seq=3 ttl=64 time=0.412 ms
Confirm that the Active server doesn't use the virtual IP address any more.
[root@osspc16]# ifconfig
eth0 ...
lo ...
Confirm that the Standby server uses the virtual IP address.
[root@osspc20]# ifconfig
eth0 ...
eth0:0 inet addr:133.137.177.143 ...
lo ...
Try to connect PostgreSQL by "psql -h delegate_IP -p port".
[user@someserver]$ psql -h 133.137.177.142 -p 9999 -l
There are the parameters about watchdog's monitoring. Specify the interval to check wd_interval, the count to retry wd_life_point, the query to check wd_lifecheck_query and finally the type of lifecheck wd_lifecheck_method.
wd_lifecheck_method = 'query'
# Method of watchdog lifecheck ('heartbeat' or 'query' or 'external')
# (change requires restart)
wd_interval = 10
# lifecheck interval (sec) > 0
wd_life_point = 3
# lifecheck retry times
wd_lifecheck_query = 'SELECT 1'
# lifecheck query to pgpool from watchdog
There are the parameters for switching the virtual IP address. Specify switching commands if_up_cmd, if_down_cmd, the path to them if_cmd_path, the command executed after switching to send ARP request arping_cmd and the path to it arping_path.
ifconfig_path = '/sbin' # ifconfig command path if_up_cmd = 'ifconfig eth0:0 inet $_IP_$ netmask 255.255.255.0' # startup delegate IP command if_down_cmd = 'ifconfig eth0:0 down' # shutdown delegate IP command arping_path = '/usr/sbin' # arping command path arping_cmd = 'arping -U $_IP_$ -w 1'
You can also use the custom scripts to bring up and bring down the virtual IP using wd_escalation_command and wd_de_escalation_command configurations.