Python script for generating a mapping of regions to the latest AMI for a given Ubuntu distribution and instance type for use in CloudFormation template.

generate-ubuntu-ami-mapping.py

#!/usr/bin/env python
import urllib2
import json
import itertools
import sys
import argparse

def groupby(data, key):
  kf = lambda x: x[key]
  result = itertools.groupby(sorted(data,None,kf), kf)
  return result

def find_latest_builds(distro, instance_type):
  builds = []
  # We should use 'with' here, but the object returned by urlopen doesn't have
  # sufficient awesome.
  f = urllib2.urlopen("https://cloud-images.ubuntu.com/query/%s/server/daily.current.txt" % distro)
  try:
    for l in f:
      builds.append(dict(zip(['instance_type', 'arch', 'region', 'ami'], l.split()[4:8])))
  finally:
    f.close()
  return filter(lambda x: x['instance_type'] == instance_type, builds)  

# Get the arguments
parser = argparse.ArgumentParser(description='Generates a mapping of regions to the latest AMI for a given Ubuntu release and instance type for use in a CloudFormation template.')
parser.add_argument('distro', type=str, help='code name of Ubuntu distribution (natty, oneiric, precise, etc.)')
parser.add_argument('instancetype', type=str, help='EC2 instance type', choices=['instance-store', 'ebs'])
args = parser.parse_args()

# Pull the builds
builds = find_latest_builds(args.distro, args.instancetype)

# Create the JSON mapping
region_arch_ami_map = { 
   region: { 
    arch: i2.next()['ami'] 
    for arch, i2 in groupby(i, 'arch') 
  } 
  for region, i in groupby(builds, 'region') 
}
print json.dumps(region_arch_ami_map, indent=2)