Find snapshot by tag, create volume from it and mount.

attach_volume.py

#! /usr/bin/python

from boto.utils import get_instance_metadata
import boto.ec2
import argparse, logging, time, os

def parsed_args():
  # parse cmd line args
  parser = argparse.ArgumentParser(description='Find snapshot by tag, create volume from it and mount.')
  parser.add_argument('--id',
                      help='ID of existing snapshot to mount')
  parser.add_argument('--tag-name',
                      help='Name of tag to filter snapshots on')
  parser.add_argument('--tag-value',
                      help='Value of tag to filter snapshots on')
  parser.add_argument('--aws-mount-point',
                      help='The desired mount point as defined by AWS. default is /dev/sdf',
                      default='/dev/sdf')
  parser.add_argument('--os-mount-point',
                      help='The desired mount point as defined by the OS, default is /dev/xvdf',
                      default='/dev/xvdf')
  parser.add_argument('--volume-type',
                      help='Type of volume to create, default is gp2',
                      default='gp2')
  return parser.parse_args();

def main():
  args = parsed_args();

  snapshot = find_snapshot(args.tag_name, args.tag_value)
 
  if(snapshot is None):
    snapshot = get_snapshot(args.id)

  volume = create_volume(snapshot, args.volume_type)
  attach_volume(volume, args.aws_mount_point, args.os_mount_point)
  set_volume_delete(args.aws_mount_point)

  logging.info('Volume attached!')
  exit(0)

def find_snapshot(tag_name, tag_value):
  logging.info('Finding snapshot for tag...')

  conn = boto.ec2.connect_to_region(current_region())

  snapshots = conn.get_all_snapshots(filters={'tag:' + tag_name: tag_value})

  snapshots.sort(date_compare)

  if(len(snapshots) > 0):
    logging.info('Snapshot found with tag %s:%s' % (tag_name, tag_value))
    return snapshots[0]
  else:
    return None

def get_snapshot(id):
  logging.info('Getting snapshot by id...')

  conn = boto.ec2.connect_to_region(current_region())

  snapshots = conn.get_all_snapshots(snapshot_ids=[id])

  if(len(snapshots) > 0):
    logging.info('Snapshot found')
    return snapshots[0]
  else:
    raise Exception('No snapshot found with id %s' % id)

def create_volume(snapshot, volume_type):
  logging.info('Creating new volume from snapshot: %s' % snapshot)

  conn = boto.ec2.connect_to_region(current_region())
  volume = conn.create_volume(zone=current_zone(), size=snapshot.volume_size, volume_type=volume_type, snapshot=snapshot)

  wait_for_volume(volume, 'available')
  return volume

def set_volume_delete(mount_point):
  logging.info('Setting volume to delete on termination...')

  metadata = get_instance_metadata()
  instanceId = metadata['instance-id']
  conn = boto.ec2.connect_to_region(current_region())
  reservations = conn.get_all_instances(instance_ids=[instanceId])
  instance = reservations[0].instances[0]

  instance.modify_attribute('blockDeviceMapping', [mount_point + '=1'])

def attach_volume(volume, aws_mount_point, os_mount_point):
  logging.info('Attaching volume to instance')

  conn = boto.ec2.connect_to_region(current_region())
  metadata = get_instance_metadata()

  volume_status = conn.attach_volume(volume_id=volume.id, instance_id=metadata['instance-id'], device=aws_mount_point)

  wait_for_volume(volume, 'in-use')
  wait_for_fstab(os_mount_point, 'present')
  return True

def wait_for_volume(volume, expected_status):
  volume_status = 'waiting'
  sleep_seconds = 2
  sleep_intervals = 30

  for counter in range(sleep_intervals):
    logging.info('elapsed: %s. status: %s.' % (sleep_seconds * counter, volume_status))

    conn = boto.ec2.connect_to_region(current_region())
    volume_status = conn.get_all_volumes(volume_ids=[volume.id])[0].status

    if volume_status == expected_status:
      break

    time.sleep(sleep_seconds)

  if volume_status != expected_status:
    raise Exception('Unable to get %s status for volume %s' % (expected_status, volume.id))

  logging.info('Volume now in %s state' % expected_status)

def wait_for_fstab(mount_point, expected_status):
  volume_status = 'not present'
  sleep_seconds = 2
  sleep_intervals = 30

  for counter in range(sleep_intervals):
    logging.info('elapsed: %s. status: %s.' % (sleep_seconds * counter, volume_status))

    try:
      os.stat(mount_point)
      volume_status = expected_status
    except: OSError
      # mount does not exist yet, try again later...

    if volume_status == expected_status:
      break

    time.sleep(sleep_seconds)

  if volume_status != expected_status:
    raise Exception('Unable to get %s status for volume %s' % (expected_status, volume.id))

  logging.info('Volume now in %s state' % expected_status)

def current_zone():
  metadata = get_instance_metadata()
  return metadata['placement']['availability-zone']

def current_region():
  zone = current_zone()
  return zone[:-1]

def date_compare(snap1, snap2):
  if snap1.start_time < snap2.start_time:
    return 1
  elif snap1.start_time == snap2.start_time:
    return 0
  return -1

if __name__ == '__main__':
  logging.getLogger().setLevel(logging.INFO)
  main()

Hi Gavin, I like what your script does. What should I be put in for --tag-name and --tag-value ? Where I can find the name and value of the tag in AWS console?

Hi, --tag-name and --tag-value should match any tags you have set on the snapshot so the script will filter snapshots by those tags. You can view / edit the tags on the Tags tab in the 'Snapshots' section of the EC2 console.