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This tutorial explains the simple way to try "Watchdog" on AWS and using the Elastic IP Address as the Virtual IP for the high availability solution.
Note: You can use watchdog with Pgpool-II in any mode: replication mode, native replication mode and raw mode.
For this example, we will use two node Pgpool-II watchdog cluster. So we will set up two Linux Amazon EC2 instances and one Elastic IP address. So for this example, do the following steps:
Launch two Linux Amazon EC2 instances. For this example, we name these instances as "instance-1" and "instance-2"
Configure the security group for the instances and allow inbound traffic on ports used by pgpool-II and watchdog.
Install the Pgpool-II on both instances.
Allocate an Elastic IP address. For this example, we will use "35.163.178.3" as an Elastic IP address"
Mostly the Pgpool-II configurations for this example will be same as in the Section 8.2, except the delegate_IP which we will not set in this example instead we will use wd_escalation_command and wd_de_escalation_command to switch the Elastic IP address to the leader/Active Pgpool-II node.
use_watchdog = on
delegate_IP = ''
...
wd_escalation_command = '$path_to_script/aws-escalation.sh'
wd_de_escalation_command = '$path_to_script/aws-de-escalation.sh'
Create the aws-escalation.sh and aws-de-escalation.sh scripts on both instances and point the wd_escalation_command and wd_de_escalation_command to the respective scripts.
Note: You may need to configure the AWS CLI first on all AWS instances to enable the execution of commands used by wd-escalation.sh and wd-de-escalation.sh. See configure AWS CLI
This script will be executed by the watchdog to assign the Elastic IP on the instance when the watchdog becomes the active/leader node. Change the INSTANCE_ID and ELASTIC_IP values as per your AWS setup values.
aws-escalation.sh:
#! /bin/sh
ELASTIC_IP=35.163.178.3
# replace it with the Elastic IP address you
# allocated from the aws console
INSTANCE_ID=i-0a9b64e449b17ed4b
# replace it with the instance id of the Instance
# this script is installed on
echo "Assigning Elastic IP $ELASTIC_IP to the instance $INSTANCE_ID"
# bring up the Elastic IP
aws ec2 associate-address --instance-id $INSTANCE_ID --public-ip $ELASTIC_IP
exit 0
This script will be executed by watchdog to remove the Elastic IP from the instance when the watchdog resign from the active/leader node.
aws-de-escalation.sh:
#! /bin/sh
ELASTIC_IP=35.163.178.3
# replace it with the Elastic IP address you
# allocated from the aws console
echo "disassociating the Elastic IP $ELASTIC_IP from the instance"
# bring down the Elastic IP
aws ec2 disassociate-address --public-ip $ELASTIC_IP
exit 0
"Configure AWS CLI", AWS Documentation: Configuring the AWS Command Line Interface.
"associate-address", AWS Documentation: associate-address reference.
"disassociate-address", AWS Documentation: disassociate-address reference.
Start Pgpool-II on each server with "-n" switch and redirect log messages to the pgpool.log file. The log message of leader/active Pgpool-II node will show the message of Elastic IP assignment.
LOG: I am the cluster leader node. Starting escalation process
LOG: escalation process started with PID:23543
LOG: watchdog: escalation started
Assigning Elastic IP 35.163.178.3 to the instance i-0a9b64e449b17ed4b
{
"AssociationId": "eipassoc-39853c42"
}
LOG: watchdog escalation successful
LOG: watchdog escalation process with pid: 23543 exit with SUCCESS.
Confirm to ping to the Elastic IP address.
[user@someserver]$ ping 35.163.178.3
PING 35.163.178.3 (35.163.178.3) 56(84) bytes of data.
64 bytes from 35.163.178.3: icmp_seq=1 ttl=64 time=0.328 ms
64 bytes from 35.163.178.3: icmp_seq=2 ttl=64 time=0.264 ms
64 bytes from 35.163.178.3: icmp_seq=3 ttl=64 time=0.412 ms
Try to connect PostgreSQL by "psql -h ELASTIC_IP -p port".
[user@someserver]$ psql -h 35.163.178.3 -p 9999 -l
To confirm if the Standby server acquires the Elastic IP when the Active server becomes unavailable, Stop the Pgpool-II on the Active server. Then, the Standby server should start using the Elastic IP address, And the Pgpool-II log will show the below messages.
LOG: remote node "172.31.2.94:9999 [Linux ip-172-31-2-94]" 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 [LEADER]
LOG: I am announcing my self as leader/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:23543
LOG: watchdog: escalation started
Assigning Elastic IP 35.163.178.3 to the instance i-0dd3e60734a6ebe14
{
"AssociationId": "eipassoc-39853c42"
}
LOG: watchdog escalation successful
LOG: watchdog escalation process with pid: 61581 exit with SUCCESS.
Confirm to ping to the Elastic IP address again.
[user@someserver]$ ping 35.163.178.3
PING 35.163.178.3 (35.163.178.3) 56(84) bytes of data.
64 bytes from 35.163.178.3: icmp_seq=1 ttl=64 time=0.328 ms
64 bytes from 35.163.178.3: icmp_seq=2 ttl=64 time=0.264 ms
64 bytes from 35.163.178.3: icmp_seq=3 ttl=64 time=0.412 ms
Try to connect PostgreSQL by "psql -h ELASTIC_IP -p port".
[user@someserver]$ psql -h 35.163.178.3 -p 9999 -l