swap-eips.sh

#!/bin/bash

# depend on awscli and jq

export AWS_DEFAULT_REGION=ap-northeast-1
export AWS_ACCESS_KEY_ID=
export AWS_SECRET_ACCESS_KEY=


instanceName="nat-instance"
echo "Start to swap eips"

# 1. Get nat-instance Id
instanceId=$(aws ec2 describe-instances --filter "Name=tag:Name,Values=${instanceName}" --query 'Reservations[].Instances[].InstanceId' --output text)
if [ "x${instanceId}" == "x" ]; then
    echo "${instanceName} does not exist" && exit 1
fi
echo "${instanceId}"

# 2. Get the current addr allocation Id
currentAllocationId=$(aws ec2 describe-addresses --filters "Name=instance-id,Values=${instanceId}" | jq '.Addresses[].AllocationId')
if [ "x${currentAllocationId}" == "x" ]; then
    echo "failed to get a current allocation Id" && exit 1
fi

# 3. Allocate a new addr
newAllocationId=$(aws ec2 allocate-address --domain vpc | jq .AllocationId)
if [ "x${newAllocationId}" == "x" ]; then
    echo "failed to allocate a new address" && exit 1
fi
echo "${newAllocationId}"

# 4. Associate a new addr to nat-instance
aws ec2 associate-address --allocation-id "${newAllocationId//\"/}" --instance "${instanceId//\"/}"
if [ $? != 0 ]; then
    echo "failed to associate a new address" && exit 1
fi

# 5. Release an old addr
aws ec2 release-address --allocation-id "${currentAllocationId//\"/}"
if [ $? != 0 ]; then
    echo "failed to release an old address" && exit 1
fi

echo "success"