AWS VIP Monitor/takeover script

vip_mon.sh

#!/bin/sh
# This script will monitor another HA node and take over a Virtual IP (VIP)
# if communication with the other node fails

# High Availability IP variables
# Other node's IP to ping and VIP to swap if other node goes down
HA_Node_IP=
VIP=

# Specify the EC2 region that this will be running in
REGION=

# Run aws-apitools-common.sh to set up default environment variables and to
# leverage AWS security credentials provided by EC2 roles
. /etc/profile.d/aws-apitools-common.sh

# Determine the instance and ENI IDs so we can reassign the VIP to the
# correct ENI.  Requires EC2 describe-instances and assign-private-ip-address
# permissions.  The following example EC2 Roles policy will authorize these
# commands:
# {
#  "Statement": [
#    {
#      "Action": [
#        "ec2:AssignPrivateIpAddresses",
#        "ec2:DescribeInstances"
#      ],
#      "Effect": "Allow",
#      "Resource": "*"
#    }
#  ]
# }

Instance_ID=`/usr/bin/curl --silent http://169.254.169.254/latest/meta-data/instance-id`
ENI_ID=`/opt/aws/bin/ec2-describe-instances $Instance_ID --region $REGION | grep eni -m 1 | awk '{print $2;}'`

echo `date` "-- Starting HA monitor"
while [ . ]; do
  pingresult=`ping -c 3 -W 1 $HA_Node_IP | grep time= | wc -l`
  if [ "$pingresult" == "0" ]; then
    echo `date` "-- HA heartbeat failed, taking over VIP"
    /opt/aws/bin/ec2-assign-private-ip-addresses -n $ENI_ID --secondary-private-ip-address $VIP --allow-reassignment --region $REGION
    pingresult=`ping -c 1 -W 1 $VIP | grep time= | wc -l`
    if [ "$pingresult" == "0" ]; then
      echo `date` "-- Restarting network"
      /sbin/service network restart > /dev/null 2>&1
    fi
    sleep 60
  fi
  sleep 2
done