dynamically-populate-etchosts-in-an-aws-ami

#! /bin/sh

# set some vars/env vars up

HFILE=/etc/hosts
HNAME_S=`/bin/hostname -s`
HNAME_F=`/bin/hostname -f`
TDATE=`/bin/date '+%Y-%m-%d %H:%M:%S'`
export JAVA_HOME=/usr/java/default
export EC2_PRIVATE_KEY=/tmp/.ec2/your-key.pem
export EC2_CERT=/tmp/.ec2/your-cert.pem
export EC2_HOME=/root/ec2/
# optional, depending on your location (default is us-east)
export EC2_URL=http://eu-west-1.ec2.amazonaws.com
PATH=$PATH:$HOME/bin:$EC2_HOME/bin
MAX_TRIES=60

# start/stop functions for OS

start() {
  # get ip address from api
  ADD=`/usr/bin/curl http://169.254.169.254/latest/meta-data/local-ipv4 2> /dev/null`
  CTR=0
  /usr/bin/printf 'Getting local ip address.\n';

  # now check var for not being dotted quad format
  while [[ ! '$ADD' =~ ^\([0-9]\{1,3\}\.\)\{3\}[0-9]\{1,3\}$ ]]; do
    /bin/sleep 1
    CTR=`expr $CTR + 1`

    # if CTR has reached MAX_TRIES then bin out
    if [ $CTR -eq $MAX_TRIES ]; then
        /usr/bin/printf 'WARNING: Cannot write $ADD to $HFILE -- Giving up after $MAX_TRIES attempts\n'
        exit 1
    fi
    done

    # if we get here $ADD is ok, so add required values to hosts file
    /usr/bin/printf '# File written by /etc/init.d/getipadd at: $TDATE\n' > $HFILE
    /usr/bin/printf '127.0.0.1\tlocalhost.localdomain\tlocalhost\n' >> $HFILE
    /usr/bin/printf '$ADD\t$HNAME_F\t$HNAME_S\n' >> $HFILE
}

stop() {
    # set host file to original value
    /usr/bin/printf '# File written by /etc/init.d/getipadd\n at: $TDATE' > $HFILE
    /usr/bin/printf '127.0.0.1\tlocalhost.localdomain\tlocalhost\n' >> $HFILE
}

case '$1' in

start)
  start
  ;;
stop)
  stop
  ;;
restart)
  stop
  sleep 5
  start
  ;;
*)
echo 'Usage: $0 {start|stop|restart}'
exit 1

esac

exit 0