ec2-get-dns

#!/usr/bin/python
#
# retreive an EC2 instance's public DNS name based on region
# and instance ID. Requires boto [pip install boto] and 
# a ~/.boto file with the user's credentials.
import sys, os

# check args, print syntax
if len(sys.argv) != 3:
	sname = os.path.basename(sys.argv[0])
	sys.stderr.write("Invalid Arguments.\n" +
		"Syntax: %s region-name instance-id\n" % sname +
		"\teg: %s us-west-2 i-12345678\n" % sname +
		"\tor: %s -s shortcut-name\n" % sname)
	exit(1)

# get info from ~/.ec2list
def getfromshort(shortname):
	user_home = os.getenv('HOME')
	if os.path.exists(user_home+'/.ec2list'):
		import re
		fh = open(user_home+'/.ec2list')
		while True:
			line = fh.readline()
			if not line:
				break
			match = re.match('^('+shortname+'):([^:]*):([^:]*)(?::([^:]*))?$', line.strip())
			if not match:
				continue
			else:
				break
		if not match:
			sys.stderr.write("Could not find %s in ~/.ec2list\n" % shortname)
			return None
		return match.groups()
	else:
		sys.stderr.write("Cannot find ~/.ec2list\n")
		return None

# prepare args
if sys.argv[1] == '-s':
	shortname = sys.argv[2]
	res = getfromshort(shortname)
	if not res:
		exit(1)
	region = res[1]
	search_id = res[2]
else:
	region = sys.argv[1]
	search_id = sys.argv[2]

# prepare connection
import boto.ec2
conn = boto.ec2.connect_to_region(region)
reservations = conn.get_all_instances()

# find
# not super efficient, but I can't find a simple
# get_instance_by_id(instance_id) function
# as long as you don't have a squillion instances
# in a single region it should be fine.
for res in reservations:
	for inst in res.instances:
		if inst.id == search_id:
			if inst.state == 'running':
				print inst.public_dns_name
				exit()
			else:
				sys.stderr.write("Instance %s not running\n" % inst.id)
				exit(1)

sys.stderr.write("Could not find instance %s in region %s\n" % (search_id,region))
exit(1)