Script to assign Public IP from Elastic IP pool for instances hosted in AWS. 'ec2-utils' and AWS CLI packages required. Instance role or access keys need to allow at least next EC2 actions: describe-addresses, associate-address and disassociate-address. Shell script is designed to be integrated with instance start-up

ipassign

#!/bin/bash
# chkconfig: 2345 99 10
# description: Set Public IP from ElasticIP pool during instance startup
# processname: ipassign
# Provides:             ipassign
# Required-Start:       
# Required-Stop:        
# Default-Start:        2 3 4 5
# Default-Stop:         
# Short-Description:    Set Public IP from ElasticIP pool during instance startup
#
#
# Developed by: Javier Sianes - jsianes@gmail.com
#

OUTPUT="text"
REGION="eu-west-1"
IPLOGFILE="/var/log/ipassign.log"
export PATH=/usr/share/pear:/usr/local/bin:/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/sbin:/opt/aws/bin:/home/ec2-user/bin

timestamp() {
  TIMESTAMP=`date -u +"%Y-%m-%dT%H:%M:%S.000Z"`
}

usage() {
  echo "$0 {start|stop|status}"
  exit 255
}

write_log() {
  timestamp
  echo "${TIMESTAMP} - ${LOG}" >> ${IPLOGFILE}
}

valid_ip() {
  RX='([1-9]?[0-9]|1[0-9]{2}|2[0-4][0-9]|25[0-5])'
  
  if [[ ${EC2PUBLICIP} =~ ^${RX}\.${RX}\.${RX}\.${RX}$ ]]
  then
    VALIDIP=1
  else
    VALIDIP=0
  fi
}

check_ec2metadata() {
  ec2-metadata >/dev/null 2>&1
  if [ $? -eq 0 ]
  then
    # Amazon Linux ec2-metadata command found
    EC2INSTANCE=`ec2-metadata -i | awk '{ print $NF; }'`
    EC2PUBLICIP=`ec2-metadata -v | awk '{ print $NF; }'`
  else
    # Checking ec2metadata command
    ec2metadata >/dev/null 2>&1
    if [ $? -eq 0 ]
    then
      # ec2metadata command found
      EC2INSTANCE=`ec2metadata --instance-id`
      EC2PUBLICIP=`ec2metadata --public-ipv4`
    else
      # No ec2metadata/ec2-metadata command found. Trying to obtain using curl requests directly
      IP_AVAILABLE=`curl --connect-timeout 5 -i http://169.254.169.254/latest/meta-data/public-ipv4 2>/dev/null | grep "200 OK" | wc -l`
      IS_AVAILABLE=`curl --connect-timeout 5 -i http://169.254.169.254/latest/meta-data/instance-id 2>/dev/null | grep "200 OK" | wc -l`
      (( INFO=${IP_AVAILABLE}+${IS_AVAILABLE} ))
  
      if [ ${INFO} -eq 2 ]
      then
        EC2INSTANCE=`curl --connect-timeout 5 http://169.254.169.254/latest/meta-data/instance-id 2>/dev/null`
        EC2PUBLICIP=`curl --connect-timeout 5 http://169.254.169.254/latest/meta-data/public-ipv4 2>/dev/null`
      else
        # ec2metadata/ec2-metadata command not found and unable to obtain metadata info using curl
        LOG="ERROR: Unable to obtain metadata information using ec2metadata/ec2-metadata command or curl requests"; write_log
        exit 127
      fi
    fi
  fi
}

check_awscli() {
  aws ec2 describe-addresses >/dev/null 2>&1
  
  if [ $? -ne 0 ]
  then
    # Incorrect instance role or invalid AWS CLI configuration
    LOG="ERROR: AWS CLI command not available. Check instance role or AWS CLI installation/configuration"; write_log
    exit 128
  fi
}

start() {
  check_ec2metadata

  # Check Public IP
  valid_ip

  if [ ${VALIDIP} -eq 0 ]
  then
    # No Public IP available. So, AWS CLI unavailable
    LOG="ERROR: There is no Public IP address attached to ${EC2INSTANCE} instance. Unable to use AWS CLI."; write_log
    exit 3
  fi
  
  # Check if AWS CLI is available
  check_awscli

  # Check if instance has a public IP from Elastic pool assigned
  PUBLICIPASSIGNED=`aws ec2 describe-addresses --output ${OUTPUT} --region ${REGION} | grep ${EC2INSTANCE} | wc -l`

  if [ ${PUBLICIPASSIGNED} -gt 0 ]
  then
    # Instance has (at least) one Pulic IP associated from Elastic pool
    IP=`aws ec2 describe-addresses --output ${OUTPUT} --region ${REGION} | grep ${EC2INSTANCE} | head -1 | awk '{ print $NF; }'`
    LOG="Instance ${EC2INSTANCE} has (at least) one Public IP address from Elastic pool in ${REGION} region (${IP})"; write_log
    exit 4
  else
    # Get IP address from Elastic pool
    IP=`aws ec2 describe-addresses --output ${OUTPUT} --region ${REGION} | grep -v 'i-' | head -1 | awk '{ print $NF; }'`

    if [ "${IP}" = "" ]
    then
      # Public IP on Elastic pool unavailable
      LOG="ERROR: Free Public IP inside Elastic pool in ${REGION} region unavailable"; write_log
      exit 5
    else
      # Attach Public IP from Elastic pool
      BOOL=0
      aws ec2 associate-address --output ${OUTPUT} --region ${REGION} --instance-id ${EC2INSTANCE} --public-ip ${IP} >/dev/null 2>&1
      EXITCODE=$?

      if [ ${EXITCODE} -eq 0 ]
      then
        LOG="${IP} Public IP from Elastic pool assigned to ${EC2INSTANCE} instance"; write_log
      else
        LOG="ERROR: (${EXITCODE}) Unable to attach ${IP} Public IP from Elastic pool to ${EC2INSTANCE} instance"; write_log
        BOOL=1
      fi

      if [ ${BOOL} -eq 0 ]
      then
        # Detaching default Public IP
        aws ec2 disassociate-address --output ${OUTPUT} --region ${REGION} --instance-id ${EC2INSTANCE} --public-ip ${EC2PUBLICIP} >/dev/null 2>&1
        EXITCODE=$?

        if [ ${EXITCODE} -eq 0 ] || [ ${EXITCODE} -eq 255 ]
        then
          LOG="Default public IP ${EC2PUBLICIP} outside Elastic pool detached from ${EC2INSTANCE} instance"; write_log
        else
          LOG="ERROR: (${EXITCODE}) Unable to detach default public IP ${EC2PUBLICIP} from ${EC2INSTANCE} instance"; write_log
          BOOL=2
        fi
      fi
      exit ${BOOL}
    fi
  fi
}

stop() {
  exit 6
}

status() {
  check_ec2metadata
  valid_ip

  if [ ${VALIDIP} -eq 0 ]
  then
    echo "No Public IP address attached to ${EC2INSTANCE} instance."
    exit 1
  fi
  
  check_awscli
  IPPRESENTINPOOL=`aws ec2 describe-addresses --output ${OUTPUT} --region ${REGION} | grep "${EC2INSTANCE}" | grep ${EC2PUBLICIP} | wc -l`
  
  if [ ${IPPRESENTINPOOL} -eq 1 ]
  then
    echo "Public IP ${EC2PUBLICIP} attached to ${EC2INSTANCE} instance in ${REGION} region belongs to ElasticIP pool"
    exit 0
  else
    echo "Public IP ${EC2PUBLICIP} attached to ${EC2INSTANCE} instance in ${REGION} region is a generic public IP NOT present in ElasticIP pool"
    exit 2
  fi
}

case "$1" in
  start)
        start
        ;;
  stop)
        stop
        ;;
  status)
        status
        ;;
  *)
        usage
        ;;
esac

Thank man, you rock!

Hi, I'm getting the following error: ERROR: (255) Unable to attach {IP omitted} Public IP from Elastic pool to i-{ID omitted} instance

If I run the following manually:

aws ec2 associate-address --instance-id i-{ID omitted} --public-ip {IP omitted}

I see:

An error occurred (InvalidParameterCombination) when calling the AssociateAddress operation: You must specify an allocation id when mapping an address to a VPC instance.

Resolved:

1. Added this below line 118

   Get Allocation id from Elastic pool

   AID=aws ec2 describe-addresses --output ${OUTPUT} --region ${REGION} | grep -v 'i-' | head -1 | awk '{ print $2; }'

2. Modified line 128 to:
   aws ec2 associate-address --output ${OUTPUT} --region ${REGION} --instance-id ${EC2INSTANCE} --allocation-id ${AID} >/dev/null 2>&1

Hi,

We tried to run this as launch script while launching the EC2 instance but it didn't work. But it works when we run this on shell and it successfully assigns Elastic IP to the instance.

Thanks