EC2 User Data script to allocate an EIP on launch.

ubuntu-allocate-eip-on-launch.sh

#!/bin/bash
#
# Associate a given elastic IP with an instance on boot.
#
# Useful in autoscaling groups with a max-size of 1, where you always want the
# same IP for a given instance.
#
INSTANCE_ID=$(curl -s http://169.254.169.254/latest/meta-data/instance-id)
AWS_DEFAULT_REGION=ap-southeast-2

# Associate this EIP on launch.
ALLOC_ID=YOUR_EIP_ALLOC_ID

echo "Updating packages..."

# Update packages.
apt-get update -y
# Force grub to update in a silent mode
DEBIAN_FRONTEND=noninteractive apt-get -y -o DPkg::options::="--force-confdef" -o DPkg::options::="--force-confold" -qq --force-yes upgrade

# Install the awscli
if ! [ -x "$(command -v aws)" ]; then
  echo "Installing awscli..."
  curl "https://awscli.amazonaws.com/awscli-exe-linux-x86_64.zip" -o "awscliv2.zip"
  yes | unzip awscliv2.zip
  yes | ./aws/install
fi

# Install jq
if ! [ -x "$(command -v jq)" ]; then
  echo "Installing jq..."
  snap install jq
fi

# Get instance creds.
# @see https://github.com/pierreg256/eip/blob/master/auto-ip.sh
# @see https://gist.github.com/fgassert/8923461
# @see https://gist.github.com/odessky/e7b8b31e3b710cf3e29e85339d4ec5e6

ROLE=$(curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/)
CR=$(curl -s http://169.254.169.254/latest/meta-data/iam/security-credentials/$ROLE/)

export AWS_ACCESS_KEY_ID=$(echo $CR | jq -r '.AccessKeyId')
export AWS_SECRET_ACCESS_KEY=$(echo $CR | jq -r '.SecretAccessKey')
export AWS_SESSION_TOKEN=$(echo $CR | jq -r '.Token')

# Now we can associate the address.
echo "Running: aws ec2 associate-address --instance-id $INSTANCE_ID --allocation-id $ALLOC_ID --allow-reassociation"
aws ec2 associate-address --instance-id $INSTANCE_ID --allocation-id $ALLOC_ID --allow-reassociation
IPv4=$(curl -s http://169.254.169.254/latest/meta-data/public-ipv4)
echo "This instance now has public IPv4 $IPv4"