Associate Elastic IP to a Bastion host running in a Auto-Scaling Group (ASG).

ec2-associate-address.sh

#!/bin/bash

set -e
set -u
set -o pipefail

export PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

# The name of the EC2 tag that holds the Elastic IP address to use.
readonly TAG_NAME='PublicIP'

readonly EC2_METADATA_URL='http://169.254.169.254/latest/meta-data'
readonly LOCK_FILE="/var/lock/$(basename -- "$0").lock"

export DEBIAN_FRONTEND=noninteractive
export DEBCONF_NONINTERACTIVE_SEEN=true

# Make sure files are 644 and directories are 755.
umask 022

[[ -e "/proc/$(cat $LOCK_FILE 2>/dev/null)" ]] || rm -f $LOCK_FILE

if (set -o noclobber; echo $$ > $LOCK_FILE) &>/dev/null; then
    # Make sure to remove the temporary
    # file when terminating, and clean-up
    # the lock-file too.
    trap \
        "rm -f $LOCK_FILE; exit" \
            HUP INT KILL TERM QUIT EXIT

    # Refresh packages index only when needed.
    UPDATE_STAMP='/var/lib/apt/periodic/update-success-stamp'
    if [[ ! -f $UPDATE_STAMP ]] || \
       (( $(date +%s) - $(date -r $UPDATE_STAMP +%s) > 300 )); then
        apt-get -qq update
    fi

    # Install AWS CLI and curl, if needed.
    PACKAGES=(curl awscli)
    for package in "${PACKAGES[@]}"; do
        if ! dpkg -s $package &>/dev/null; then
            apt-get -qq install --assume-yes $package >/dev/null
        fi
    done

    # Fetch the EC2 instance ID.
    INSTANCE_ID=$(curl -s ${EC2_METADATA_URL}/instance-id)

    # Extract the region name.
    REGION=$(curl -s ${EC2_METADATA_URL}/placement/availability-zone | sed -e 's/\w$//')

    # Fetch the EC2 instance tag which contains
    # the Elastic IP that should be used when
    # requesting the re-assotiation.
    PUBLIC_IP_ADDRESS=$(aws ec2 describe-tags \
        --query 'Tags[*].Value' \
        --filters "Name=resource-id,Values=${INSTANCE_ID}" "Name=key,Values=${TAG_NAME}" \
        --region $REGION --output 'text' 2>/dev/null)

    # Make sure that the EC2 tag was actually set.
    if [[ "x${PUBLIC_IP_ADDRESS}" == "x" ]]; then
        echo "The '${TAG_NAME}' tag is empty or has not been set, aborting..."
        exit 1
    fi

    # Request the Elastic IP address to
    # be assigned to this EC2 instance.
    aws ec2 associate-address \
        --public-ip $PUBLIC_IP_ADDRESS \
        --instance-id $INSTANCE_ID \
        --region $REGION

    rm -f $LOCK_FILE &>/dev/null

    # Reset traps to their default behaviour.
    trap - HUP INT KILL TERM QUIT EXIT
else
    echo "Unable to create lock file (current owner: "$(cat $LOCK_FILE 2>/dev/null)")."
    exit 1
fi