pgpool-II 4.2.20 Documentation
PrevUpChapter 8. Configuration ExamplesNext

8.3. AWS Configuration Example

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.

8.3.1. AWS Setup

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:

8.3.2. Pgpool-II configurations

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'

8.3.3. escalation and de-escalation Scripts

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

8.3.3.1. escalation script

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

8.3.3.2. de-escalation script

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

AWS Command References

"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.

8.3.4. Try it out

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

8.3.5. Switching Elastic IP

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

PrevHomeNext
Pgpool-II + Watchdog Setup ExampleUpAurora Configuration Example