Robust script to retrieve SSH public key into authorized_keys for EC2 instances

gistfile1.sh

#!/bin/bash
# vim:set ts=4 sw=4 et ai:
# Retrieve the SSH public key and install it for subsequent login attempts.

AUTHORIZED_KEYS=/root/.ssh/authorized_keys

TMP_KEY=/tmp/openssh_id.pub
CURL=/usr/bin/curl
CURLOPTS="--retry 3 --retry-delay 2 --silent --fail -o $TMP_KEY"

KEY_URL=http://169.254.169.254/1.0/meta-data/public-keys/0/openssh-key
KEY_FILE=/mnt/openssh_id.pub

SUCCESS=0
ATTEMPT=0
MAX_ATTEMPTS=10

if [ ! -d `dirname $AUTHORIZED_KEYS` ]; then
	mkdir -p -m 700 `dirname $AUTHORIZED_KEYS`
fi

while [ $SUCCESS -eq 0 -a $ATTEMPT -lt $MAX_ATTEMPTS ] ; do
	# attempt to retrieve the SSH public key and install it
	if [ -f $KEY_FILE ] ; then
		cat $KEY_FILE > $AUTHORIZED_KEYS
		echo "SSH key added to $AUTHORIZED_KEYS from $KEY_FILE"
		SUCCESS=1
	else
		$CURL $CURLOPTS $KEY_URL
		if [ $? -eq 0 -a -f $TMP_KEY ]; then
			cat $TMP_KEY > $AUTHORIZED_KEYS
			echo "SSH key added to $AUTHORIZED_KEYS from $KEY_URL"
			rm -f $TMP_KEY
			SUCCESS=1
		fi
	fi

	# print out status and wait for a bit if we failed
	ATTEMPT=$(($ATTEMPT + 1))
	if [ $SUCCESS -eq 1 ]; then
		echo "SSH key retrieval attempt $ATTEMPT failed"
		sleep 5
	fi
done

# either we got it or we just gave up
if [ -f $AUTHORIZED_KEYS ]; then
	chmod 600 $AUTHORIZED_KEYS
else
	echo "-=[ FATAL ]=- SSH key could not be retrieved!!!"
fi