pgpool-II 4.3.7 Documentation
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# 8.4. 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.

## 8.4.1. 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:

- 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"

## 8.4.2. 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'

## 8.4.3. 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

### 8.4.3.1. 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

### 8.4.3.2. 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.

## 8.4.4. 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

## 8.4.5. 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

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