vol-agent

vol-agent.py

import sys
import subprocess
import requests
import os

# The purpose of this script is to find look for unmounted volumes, and mount them. If a volume is unitialized, it
# will initialize as ext4.
#
# The simplest way to run this is via cron. Use the following crontab entry
#
#    */1 * * * * python /somepath/agent.py >> /var/log/vol-agent.log
#
# This script will act based on the following stimuli:
#
# 1. A volume has been attached to the VM, e.g. via 
#        nova volume-attach <VM-UUID> <Volume-UUID>
# 2. The VM's metadata has been updated to include the list of volumes that must be auto-mounted.
#        nova meta <VM-UUID> set volumes="space delimited volume-UUIDs"
#    
# This script will then mount the specified volumes under
#
#    /mnt/slaves/<volume-UUID>
#
# Feel free to modify to the default conventions.
#
# To unmount a volume, follow the same type of stimuli
#
# 1. Remove the volume's UUID from the metadata. Simply remove the volume's UUID from the value of the 
# `volumes` parameter in the `nova meta` command.
# 2. Detach the volume via `nova volume-detach <VM-UUID> <Volume-UUID>`
#


# Parses `lsblk` output to determine uninitialized volumes.
def parse_lsblk(out):
    blkDict = []
    for l in out:
        d = {}
        for t in l.split():
            k, v = t.split('=', 1)
            d[k] = v[1:-1]
        blkDict.append(d)
    return blkDict

# Run `lsblk` to find uninitialized volumes. If found one, initialize as ext4 file system
cmd = ['lsblk', '--bytes', '--pairs', '--output', 'KNAME,FSTYPE,UUID']
p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
out = p.communicate()
out = out[0].splitlines()
parsed = parse_lsblk(out)

for volume in parsed:
    if volume['FSTYPE'] == '':
        # Initialize the volume
        print "Initializing %s" % volume['KNAME']
        cmd = ['mkfs', '-t', 'ext4', '/dev/%s' % volume['KNAME']]
        p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
        out = p.communicate()

#
# Find the list of volumes that must be mounted.
r = requests.get('http://169.254.169.254/openstack/latest/meta_data.json')
if r.status_code != 200:
    sys.exit(0)
meta = r.json()["meta"]
volumes = meta["volumes"] or ''
volumes = [] or volumes.split(',')

# Unmount removed
try:
    os.makedirs('/mnt/slaves')
except:
    pass

mounted = os.listdir('/mnt/slaves')
for m in mounted:
    if m not in volumes:
        print "Unmounting /mnt/slaves/%s" % m
        cmd = ['umount', '/mnt/slaves/' + m]
        p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
        out = p.communicate()

for volume in (volume for volume in volumes if len(volume) > 0):
    disk = '/dev/disk/by-id/virtio-' + volume[:20]
    if not os.path.exists(disk):
        sys.exit(0)
    device = os.path.realpath('/dev/disk/by-id/' + os.readlink(disk))
    try:
        os.makedirs('/mnt/slaves/' + volume)
    except:
        pass

    try:
        print ("Mounting %s at /mnt/slaves/%s" % (device, volume))
        cmd = ['mount', device, '/mnt/slaves/' + volume]
        p = subprocess.Popen(cmd, stdout=subprocess.PIPE)
        out = p.communicate()
    except:
        pass