software/kvm: Implement downloadable images

Downloadable images are enabled when key image-url-list (described in
instance-kvm-input-schema.json) is present.

Images are downloaded outside of partition processing, as this can take a lot
of time by template/image-download-controller.py

Configuration is checked and cleaned up by
template/image-download-config-creator.py

Promises are used for:

 * checking if the current configuration from the request has been processed
 * checking status of configuration generation, image download process and
   checksum validity

Details about errors are exposed by using monitor stack provided HTTP server,
so that user is able to take informed decision about how to fix the problem.

software/kvm/buildout.hash.cfg

@@ -15,11 +15,11 @@
 
 [template]
 filename = instance.cfg.in
-md5sum = b36b6b3ccb15758d99f3b6258b141db9
+md5sum = e6d5c7bb627b4f1d3e7c99721b7c58fe
 
 [template-kvm]
 filename = instance-kvm.cfg.jinja2
-md5sum = fb4d76a83ff7c2d0f205d52fb314a9ee
+md5sum = aa734942801ac62eeccaba43926a0a27
 
 [template-kvm-cluster]
 filename = instance-kvm-cluster.cfg.jinja2.in
@@ -55,7 +55,7 @@ md5sum = b7e87479a289f472b634a046b44b5257
 
 [template-kvm-run]
 filename = template/template-kvm-run.in
-md5sum = c319ca536b6bac5425245fae1684ca49
+md5sum = dd1f581f34cf5a0b627576771347c710
 
 [template-kvm-controller]
 filename = template/kvm-controller-run.in
@@ -80,3 +80,11 @@ md5sum = 599dbbbd438fe7801e3f8642ae9e9a78
 [template-httpd]
 filename = instance-kvm-http.cfg.in
 md5sum = d657884d02105deffddee0edae4b50a6
+
+[image-download-controller]
+_update_hash_filename_ = template/image-download-controller.py
+md5sum = 7e4b54f8172c364bd12d28b07f8b1600
+
+[image-download-config-creator]
+_update_hash_filename_ = template/image-download-config-creator.py
+md5sum = 7f6cd75096695922fddbba1c9292cef5

software/kvm/instance-kvm-input-schema.json

@@ -367,6 +367,12 @@
       "type": "string",
       "format": "uri",
       "default": "http://git.erp5.org/gitweb/slapos.git/blob_plain/HEAD:/software/apache-frontend/software.cfg"
+    },
+    "image-url-list": {
+      "title": "List of URLs images to download",
+      "description": "The list shall be list of direct URLs to images, followed by hash (#), then by image MD5SUM. Each image shall appear on newline, like: \"https://example.com/image.iso#06226c7fac5bacfa385872a19bb99684<newline>https://example.com/another-image.iso#31b40d58b18e038498ddb46caea1361c\". They will be provided in KVM image list according to the order on the list. After updating the list, the instance has to be restarted to refresh it. Amount of images is limited to 4, and one image can be maximum 5G. Image will be downloaded and checked against its MD5SUM 4 times, then it will be considered as impossible to download with given MD5SUM. Each image has to be downloaded in time shorter than 4 hours, so in case of very slow images to access, it can take up to 16 hours to download all of them. Note: The instance has to be restarted in order to update the list of available images in the VM.",
+      "type": "string",
+      "textarea": "true"
     }
   }
 }

software/kvm/instance-kvm.cfg.jinja2

@@ -9,6 +9,7 @@
 {% set instance_type = slapparameter_dict.get('type', 'standalone') -%}
 {% set nat_rule_list = slapparameter_dict.get('nat-rules', '22 80 443') -%}
 {% set disk_device_path = slapparameter_dict.get('disk-device-path', None) -%}
+{% set image_url_list_enabled = 'image-url-list' in slapparameter_dict %}
 {% set extends_list = [] -%}
 {% set part_list = [] -%}
 
@@ -51,6 +52,11 @@ public = ${:srv}/public/
 cron-entries = ${:etc}/cron.d
 crontabs = ${:etc}/crontabs
 cronstamps = ${:etc}/cronstamps
+{%- if image_url_list_enabled %}
+image-repository = ${:srv}/image-repository
+image-url-list-var = ${:var}/image-url-list
+image-url-list-expose = ${monitor-directory:private}/image-url-list
+{%- endif %}
 
 [create-mac]
 recipe = slapos.cookbook:generate.mac
@@ -65,6 +71,108 @@ recipe = slapos.cookbook:generate.password
 storage-path = ${directory:srv}/passwd
 bytes = 8
 
+{% if image_url_list_enabled %}
+## image-url-list support BEGIN
+[empty-file-state-base-promise]
+<= monitor-promise-base
+module = check_file_state
+name = ${:_buildout_section_name_}.py
+config-state = empty
+# It's very hard to put the username and password correctly, after schema://
+# and before the host, as it's not the way how one can use monitor provided
+# information, so just show the information in the URL
+config-url = ${monitor-base:base-url}/private/image-url-list/${:filename} with username ${monitor-publish-parameters:monitor-user} and password ${monitor-publish-parameters:monitor-password}
+
+[image-url-list-source-config]
+# generates configuration of the image from the user parameter
+# special "magic" is used, to properly support multiline image-url-list
+# but in the same time correctly generate the configuration file
+recipe = slapos.recipe.template:jinja2
+template = inline:
+{#- Do special trick to support image-url-list being None, if key is present with value "" #}
+{%- raw %}
+  {{ slap_parameter.get('image-url-list') or '' }}
+{% endraw -%}
+context =
+  section slap_parameter slap-parameter
+rendered = ${directory:etc}/image-url-list.conf
+
+[image-url-list-processed-config]
+# compares if the current configuration has been used by
+# the image-url-list-download, if not, exposes it as not empty file with
+# information
+recipe = slapos.recipe.build
+install =
+  import os
+  import hashlib
+  if not os.path.exists(location):
+    os.mkdir(location)
+  with open('${:state-file}', 'w') as state_handler:
+    try:
+      with open('${:config-file}', 'rb') as config_handler, open('${:processed-md5sum}') as processed_handler:
+        config_md5sum = hashlib.md5(config_handler.read()).hexdigest()
+        processed_md5sum = processed_handler.read()
+        if config_md5sum == processed_md5sum:
+          state_handler.write('')
+        else:
+          state_handler.write('config %s != processed %s' % (config_md5sum, processed_md5sum))
+    except Exception as e:
+      state_handler.write(str(e))
+
+update = ${:install}
+config-file = ${image-url-list-source-config:rendered}
+state-filename = image-url-list-processed-config.state
+state-file = ${directory:image-url-list-expose}/${:state-filename}
+processed-md5sum = ${directory:image-url-list-var}/update-image-processed.md5sum
+
+[image-url-list-processed-config-promise]
+# promise to check if the configuration provided by the user has been already
+# processed by the image-url-list-download script, which runs asynchronously
+<= empty-file-state-base-promise
+filename = ${image-url-list-processed-config:state-filename}
+config-filename = ${image-url-list-processed-config:state-file}
+
+[image-url-list-json-config]
+# generates json configuration from user configuration
+recipe = plone.recipe.command
+command = {{ python_executable }} {{ image_download_config_creator }} ${image-url-list-source-config:rendered} ${:rendered} ${directory:image-repository} ${:error-state-file}
+update-command = ${:command}
+rendered = ${directory:image-url-list-var}/image-url-list.json
+error-state-filename = image-url-list-json-config-error.txt
+error-state-file = ${directory:image-url-list-expose}/${:error-state-filename}
+
+[image-url-list-config-state-promise]
+# promise to check if configuration has been parsed without errors
+<= empty-file-state-base-promise
+filename = ${image-url-list-json-config:error-state-filename}
+config-filename = ${image-url-list-json-config:error-state-file}
+
+[image-url-list-download-wrapper]
+# wrapper to execute image-url-list-download on each run
+recipe = slapos.cookbook:wrapper
+wrapper-path = ${directory:scripts}/image-updater
+command-line = {{ python_executable }} {{ image_download_controller }} ${image-url-list-json-config:rendered} {{ curl_executable_location }} ${:md5sum-state-file} ${:error-state-file} ${image-url-list-processed-config:processed-md5sum}
+md5sum-state-filename = image-download-controller-md5sum-fail.json
+md5sum-state-file = ${directory:image-url-list-expose}/${:md5sum-state-filename}
+error-state-filename = image-download-controller-error.text
+error-state-file = ${directory:image-url-list-expose}/${:error-state-filename}
+hash-existing-files = ${buildout:directory}/software_release/buildout.cfg
+
+[image-url-list-download-md5sum-promise]
+# promise to report errors with problems with calculating md5sum of the
+# downloaded images
+<= empty-file-state-base-promise
+filename = ${image-url-list-download-wrapper:md5sum-state-filename}
+config-filename = ${image-url-list-download-wrapper:md5sum-state-file}
+
+[image-url-list-download-state-promise]
+# promise to report errors during download
+<= empty-file-state-base-promise
+filename = ${image-url-list-download-wrapper:error-state-filename}
+config-filename = ${image-url-list-download-wrapper:error-state-file}
+## image-url-list support END
+{% endif %} {# if image_url_list_enabled #}
+
 [kvm-controller-parameter-dict]
 python-path = {{ python_eggs_executable }}
 vnc-passwd = ${gen-passwd:passwd}
@@ -85,6 +193,11 @@ vnc-ip = ${:ipv4}
 vnc-port = 5901
 
 default-cdrom-iso = {{ debian_amd64_netinst_location }}
+{% if image_url_list_enabled %}
+image-url-list-json-config = ${image-url-list-json-config:rendered}
+{% else %}
+image-url-list-json-config =
+{% endif %}
 nbd-host = ${slap-parameter:nbd-host}
 nbd-port = ${slap-parameter:nbd-port}
 nbd2-host = ${slap-parameter:nbd2-host}
@@ -708,6 +821,7 @@ nbd-port = 1024
 nbd-host =
 nbd2-port = 1024
 nbd2-host =
+image-url-list =
 
 enable-device-hotplug = False
 ram-size = 1024
@@ -759,6 +873,9 @@ keyboard-layout-language = fr
 {% set key_list =  v.split('\n') -%}
 {{ k }} =
   {{ key_list | join('\n  ') }}
+{% elif k == 'image-url-list' %}
+{# needs to decorate possibly multiline or maybe unsafe value #}
+{{ k }} = {{ dumps(v) }}
 {% else -%}
 {{ k }} = {{ v }}
 {% endif -%}
@@ -833,6 +950,13 @@ parts =
   cron-service
   cron-entry-logrotate
   frontend-promise
+{% if image_url_list_enabled %}
+  image-url-list-download-wrapper
+  image-url-list-config-state-promise
+  image-url-list-download-md5sum-promise
+  image-url-list-download-state-promise
+  image-url-list-processed-config-promise
+{% endif %}
 {% if additional_frontend %}
   frontend-additional-promise
 {% endif %}

software/kvm/instance.cfg.in

@@ -83,6 +83,8 @@ extra-context =
   raw dcron_executable_location ${dcron:location}/sbin/crond
   raw debian_amd64_netinst_location ${debian-amd64-netinst.iso:location}/${debian-amd64-netinst.iso:filename}
   raw file_download_script ${file-download-script:location}/${file-download-script:filename}
+  raw image_download_controller ${image-download-controller:target}
+  raw image_download_config_creator ${image-download-config-creator:target}
   raw logrotate_cfg ${template-logrotate-base:rendered}
   raw novnc_location ${noVNC:location}
   raw netcat_bin ${netcat:location}/bin/netcat

software/kvm/software.cfg

@@ -190,6 +190,14 @@ context =
     raw openssl_executable_location ${openssl:location}/bin/openssl
     raw template_apache_conf ${template-apache-conf:location}/${template-apache-conf:filename}
 
+[image-download-controller]
+recipe = slapos.recipe.build:download
+url = ${:_profile_base_location_}/${:_update_hash_filename_}
+mode = 640
+
+[image-download-config-creator]
+<= image-download-controller
+
 [versions]
 websockify = 0.9.0
 

software/kvm/template/image-download-config-creator.py

+#!/usr/bin/env python
+
+import hashlib
+import json
+import re
+import sys
+
+
+if __name__ == "__main__":
+  source_configuration, destination_configuration, \
+    destination_directory, error_state_file = sys.argv[1:]
+  md5sum_re = re.compile(r"^([a-fA-F\d]{32})$")
+  image_prefix = 'image_'
+  maximum_image_amount = 4
+
+  # build currently wanted list
+  configuration_dict = {
+    'destination-directory': destination_directory,
+  }
+  image_list = []
+  error_list = []
+  print('INF: Storing errors in %s' % (error_state_file,))
+  with open(source_configuration, 'rb') as fh:
+    image_number = 0
+    data = fh.read()
+    configuration_dict['config-md5sum'] = hashlib.md5(data).hexdigest()
+    for entry in data.decode('utf-8').split():
+      split_entry = entry.split('#')
+      if len(split_entry) != 2:
+        error_list.append('ERR: entry %r is incorrect' % (entry,))
+        continue
+      url, md5sum = split_entry
+      if not md5sum_re.match(md5sum):
+        error_list.append('ERR: checksum in entry %r is malformed' % (entry, ))
+        continue
+      if md5sum not in [q['md5sum'] for q in image_list]:
+        image_number += 1
+        image_list.append({
+          'md5sum': md5sum,
+          'url': url,
+          'destination': md5sum,
+          'destination-tmp': md5sum + '_tmp',
+          'link': 'image_%03i' % (image_number,),
+        })
+      else:
+        print('INF: checksum %s repeated, used url %s' % (url, ))
+  image_amount = len(image_list)
+  if image_amount > maximum_image_amount:
+    error_list.append(
+      'ERR: Amount of images is %s, which is bigger than maximum (%s)' % (
+        image_amount, maximum_image_amount))
+  else:
+    configuration_dict['image-list'] = image_list
+  error_amount = len(error_list)
+  configuration_dict['error-amount'] = error_amount
+  with open(destination_configuration, 'w') as fh:
+    json.dump(configuration_dict, fh, indent=2)
+  with open(error_state_file, 'w') as fh:
+    if error_amount == 0:
+      print('INF: Configuration generated without errors')
+      fh.write('')
+    else:
+      print('ERR: Configuration generated with %s errors' % (error_amount,))
+      fh.write('\n'.join(error_list))
+  sys.exit(error_amount)

software/kvm/template/image-download-controller.py

+#!/usr/bin/env python
+
+import hashlib
+import json
+import os
+import re
+import subprocess
+import sys
+
+
+# stolen from download_file.in
+def md5Checksum(file_path):
+  with open(file_path, 'rb') as fh:
+    m = hashlib.md5()
+    while True:
+      data = fh.read(8192)
+      if not data:
+          break
+      m.update(data)
+    return m.hexdigest()
+
+
+# Note: Assuring only one running instance is not done, as this script is only
+#       run from supervisord, which does it already
+if __name__ == "__main__":
+  configuration, curl, md5sum_fail_file, error_state_file, \
+    processed_md5sum = sys.argv[1:]
+  error_list = []
+  md5sum_re = re.compile(r"^([a-fA-F\d]{32})$")
+  image_prefix = 'image_'
+
+  # build currently wanted list
+  with open(configuration) as fh:
+    try:
+      config = json.load(fh)
+    except Exception as e:
+      print('ERR: Problem loading configuration: %s' % (e,))
+      sys.exit(1)
+
+  if config['error-amount'] != 0:
+    print('ERR: There are problems with configuration')
+
+  print('INF: Storing errors in %s' % (error_state_file,))
+  # clean the destination directory
+  file_to_keep_list = []
+  for image in config['image-list']:
+    file_to_keep_list.append(image['destination'])
+    file_to_keep_list.append(image['link'])
+  for fname in os.listdir(config['destination-directory']):
+    if fname not in file_to_keep_list:
+      print('INF: Removing obsolete %s' % (fname,))
+      os.remove(os.path.join(config['destination-directory'], fname))
+
+  # prepare state dicts
+  # current and new are used to remove not existing configurations
+  # and also to allow re-add some configuration
+  try:
+    with open(md5sum_fail_file) as fh:
+      md5sum_state_dict = json.load(fh)
+  except Exception:
+    md5sum_state_dict = {}
+  new_md5sum_state_dict = {}
+
+  # fetch the wanted list
+  for image in config['image-list']:
+    destination = os.path.join(
+      config['destination-directory'], image['destination'])
+    if os.path.exists(destination):
+      if md5Checksum(destination) == image['md5sum']:
+        print('INF: %s : already downloaded' % (image['url'],))
+        continue
+      else:
+        print('INF: %s : Removed, as expected checksum does not match %s' % (
+          image['url'], image['md5sum']))
+        os.remove(destination)
+    # key is str, as the dict is dumped to JSON which does not accept tuples
+    md5sum_state_key = '%s#%s' % (image['url'], image['md5sum'])
+    md5sum_state_amount = md5sum_state_dict.get(md5sum_state_key, 0)
+    if md5sum_state_amount >= 4:
+      new_md5sum_state_dict[md5sum_state_key] = md5sum_state_amount
+      error_list.append(
+        'ERR: %s : Checksum is incorrect after %s tries, will not retry' % (
+          image['url'], md5sum_state_amount))
+      continue
+    print('INF: %s : Downloading' % (image['url'],))
+    download_success = True
+    destination_tmp = os.path.join(
+      config['destination-directory'], image['destination-tmp'])
+    try:
+      subprocess.check_output([
+        curl,
+        '--insecure',  # allow any download
+        '--location',  # follow redirects
+        '--no-progress-meter',  # do not tell too much
+        '--max-time', '14400',  # maximum time for download is 4 hours
+        '--max-filesize', '5368709120',  # maximum 5G for an image
+        '--output', destination_tmp, image['url']],
+        stderr=subprocess.STDOUT)
+    except subprocess.CalledProcessError as e:
+      error_list.append('ERR: %s : Problem while downloading: %r' % (
+        image['url'], e.output.strip()))
+      continue
+    if not(os.path.exists(destination_tmp)):
+      error_list.append('ERR: %s : Image disappeared, will retry later')
+      continue
+    computed_md5sum = md5Checksum(destination_tmp)
+    if computed_md5sum != image['md5sum']:
+      try:
+        os.remove(destination_tmp)
+      except Exception:
+        pass
+      error_list.append(
+        'ERR: %s : MD5 mismatch expected is %s but got instead %s' % (
+          image['url'], image['md5sum'], computed_md5sum))
+      # Store yet another failure while computing md5sum for this
+      new_md5sum_state_dict[md5sum_state_key] = md5sum_state_amount + 1
+    else:
+      os.rename(destination_tmp, destination)
+      print('INF: %s : Stored with checksum %s' % (
+        image['url'], image['md5sum']))
+  for image in config['image-list']:
+    destination = os.path.join(
+      config['destination-directory'], image['destination'])
+    link = os.path.join(config['destination-directory'], image['link'])
+    if os.path.exists(destination):
+      if os.path.lexists(link):
+        if not os.path.islink(link):
+          os.remove(link)
+        if os.path.islink(link) and os.readlink(link) != destination:
+            os.remove(link)
+      if not os.path.lexists(link):
+        print('INF: %s : Symlinking %s -> %s' % (
+          image['url'], link, destination))
+        os.symlink(destination, link)
+  with open(md5sum_fail_file, 'w') as fh:
+    if new_md5sum_state_dict != {}:
+      json.dump(new_md5sum_state_dict, fh, indent=2)
+    else:
+      # if no problems reported, just empty the file
+      fh.write('')
+  with open(error_state_file, 'w') as fh:
+    fh.write('\n'.join(error_list))
+  with open(processed_md5sum, 'w') as fh:
+    fh.write(config['config-md5sum'])
+  sys.exit(len(error_list))

software/kvm/template/template-kvm-run.in

@@ -15,6 +15,7 @@ import shutil
 from random import shuffle
 import glob
 import re
+import json
 
 import ssl
 
@@ -98,6 +99,8 @@ enable_device_hotplug = '{{ parameter_dict.get("enable-device-hotplug") }}'.lowe
 
 logfile = '{{ parameter_dict.get("log-file") }}'
 
+image_url_list_json_config = '{{ parameter_dict.get("image-url-list-json-config") }}'
+
 if hasattr(ssl, '_create_unverified_context') and url_check_certificate == 'false':
   opener = FancyURLopener(context=ssl._create_unverified_context())
 else:
@@ -366,11 +369,27 @@ for nbd_ip, nbd_port in nbd_list:
       kvm_argument_list.extend([
           '-drive',
           'file=nbd:[%s]:%s,media=cdrom' % (nbd_ip, nbd_port)])
-# If no NBD is specified/available: use internal disk image
 else:
+  image_url_list_used = False
+  if image_url_list_json_config:
+    # Support image-url-list
+    with open(image_url_list_json_config) as fh:
+      image_config = json.load(fh)
+    if image_config['error-amount'] == 0:
+      for image in sorted(image_config['image-list'], key=lambda k: k['link']):
+        link = os.path.join(image_config['destination-directory'], image['link'])
+        if os.path.exists(link) and os.path.islink(link):
+          image_url_list_used = True
+          kvm_argument_list.extend([
+            '-drive',
+            'file=%s,media=cdrom' % (link,)
+          ])
+  if not image_url_list_used:
+    # If no NBD is specified/available not downloadable image: use internal disk image
     kvm_argument_list.extend([
         '-drive', 'file=%s,media=cdrom' % default_cdrom_iso
     ])
 
+
 print('Starting KVM: \n %s' % ' '.join(kvm_argument_list))
 os.execv(qemu_path, kvm_argument_list)

software/kvm/test/test.py

@@ -28,15 +28,19 @@
 import six.moves.http_client as httplib
 import json
 import os
+import hashlib
+import psutil
 import requests
 import six
 import slapos.util
 import sqlite3
 from six.moves.urllib.parse import parse_qs, urlparse
 import unittest
+import subprocess
 
 from slapos.recipe.librecipe import generateHashFromFiles
 from slapos.testing.testcase import makeModuleSetUpAndTestCaseClass
+from slapos.slap.standalone import SlapOSNodeCommandError
 
 has_kvm = os.access('/dev/kvm', os.R_OK | os.W_OK)
 skipUnlessKvm = unittest.skipUnless(has_kvm, 'kvm not loaded or not allowed')
@@ -479,3 +483,192 @@ class TestInstanceNbdServer(InstanceTestCase):
     )
     self.assertIn('<title>Upload new File</title>', result.text)
     self.assertIn("WARNING", connection_parameter_dict['status_message'])
+
+
+@skipUnlessKvm
+class TestImageUrlList(InstanceTestCase):
+  __partition_reference__ = 'iul'
+
+  @classmethod
+  def getInstanceSoftwareType(cls):
+    return 'default'
+
+  @classmethod
+  def getInstanceParameterDict(cls):
+    # start with empty, but working configuration
+    return {}
+
+  def tearDown(self):
+    # clean up the instance for other tests
+    # 1st remove all images...
+    self.rerequestInstance({'image-url-list': ''})
+    self.slap.waitForInstance(max_retry=10)
+    # 2nd ...move instance to "default" state
+    self.rerequestInstance({})
+    self.slap.waitForInstance(max_retry=10)
+
+  def rerequestInstance(self, parameter_dict, state='started'):
+    software_url = self.getSoftwareURL()
+    software_type = self.getInstanceSoftwareType()
+    return self.slap.request(
+        software_release=software_url,
+        software_type=software_type,
+        partition_reference=self.default_partition_reference,
+        partition_parameter_kw=parameter_dict,
+        state=state)
+
+  fake_image, = (
+      "https://shacache.nxdcdn.com/shacache/05105cd25d1ad798b71fd46a206c9b73d"
+      "a2c285a078af33d0e739525a595886785725a68811578bc21f75d0a97700a66d5e75bc"
+      "e5b2721ca4556a0734cb13e65",)
+  fake_image_md5sum = "c98825aa1b6c8087914d2bfcafec3058"
+  fake_image2, = (
+      "https://shacache.nxdcdn.com/shacache/54f8a83a32bbf52602d9d211d592ee705"
+      "99f0c6b6aafe99e44aeadb0c8d3036a0e673aa994ffdb28d9fb0de155720123f74d814"
+      "2a74b7675a8d8ca20476dba6e",)
+  fake_image2_md5sum = "d4316a4d05f527d987b9d6e43e4c2bc6"
+  fake_image_wrong_md5sum = "c98825aa1b6c8087914d2bfcafec3057"
+
+  def raising_waitForInstance(self, max_retry):
+    with self.assertRaises(SlapOSNodeCommandError):
+      self.slap.waitForInstance(max_retry=max_retry)
+
+  def test(self):
+    partition_parameter_kw = {
+      'image-url-list': "%s#%s\n%s#%s" % (
+        self.fake_image, self.fake_image_md5sum, self.fake_image2,
+        self.fake_image2_md5sum)
+    }
+    self.rerequestInstance(partition_parameter_kw)
+    self.slap.waitForInstance(max_retry=10)
+    # check that image is correctly downloaded and linked
+    image_repository = os.path.join(
+      self.computer_partition_root_path, 'srv', 'image-repository')
+    image = os.path.join(image_repository, self.fake_image_md5sum)
+    image_link = os.path.join(image_repository, 'image_001')
+    self.assertTrue(os.path.exists(image))
+    with open(image, 'rb') as fh:
+      image_md5sum = hashlib.md5(fh.read()).hexdigest()
+    self.assertEqual(image_md5sum, self.fake_image_md5sum)
+    self.assertTrue(os.path.islink(image_link))
+    self.assertEqual(os.readlink(image_link), image)
+
+    image2 = os.path.join(image_repository, self.fake_image2_md5sum)
+    image2_link = os.path.join(image_repository, 'image_002')
+    self.assertTrue(os.path.exists(image2))
+    with open(image2, 'rb') as fh:
+      image2_md5sum = hashlib.md5(fh.read()).hexdigest()
+    self.assertEqual(image2_md5sum, self.fake_image2_md5sum)
+    self.assertTrue(os.path.islink(image2_link))
+    self.assertEqual(os.readlink(image2_link), image2)
+
+    # check that the image is NOT YET available in kvm
+    with self.slap.instance_supervisor_rpc as instance_supervisor:
+      kvm_pid = [q for q in instance_supervisor.getAllProcessInfo()
+                 if 'kvm-' in q['name']][0]['pid']
+      kvm_process = psutil.Process(kvm_pid)
+      cmd_line = ''.join(kvm_process.cmdline())
+      self.assertNotIn(
+        'srv/image-repository/image_001,media=cdrom',
+        cmd_line
+      )
+      self.assertNotIn(
+        'srv/image-repository/image_002,media=cdrom',
+        cmd_line
+      )
+
+    # mimic the requirement: restart the instance by requesting it stopped and
+    # then started started, like user have to do it
+    self.rerequestInstance(partition_parameter_kw, state='stopped')
+    self.slap.waitForInstance(max_retry=1)
+    self.rerequestInstance(partition_parameter_kw, state='started')
+    self.slap.waitForInstance(max_retry=1)
+
+    # now the image is available in the kvm
+    with self.slap.instance_supervisor_rpc as instance_supervisor:
+      kvm_pid = [q for q in instance_supervisor.getAllProcessInfo()
+                 if 'kvm-' in q['name']][0]['pid']
+      kvm_process = psutil.Process(kvm_pid)
+      cmd_line = ''.join(kvm_process.cmdline())
+      self.assertIn(
+        'srv/image-repository/image_001,media=cdrom',
+        cmd_line
+      )
+      self.assertIn(
+        'srv/image-repository/image_002,media=cdrom',
+        cmd_line
+      )
+
+    # cleanup of images works, also asserts that configuration changes are
+    # reflected
+    self.rerequestInstance({'image-url-list': ''})
+    self.slap.waitForInstance(max_retry=2)
+    self.assertEqual(
+      os.listdir(image_repository),
+      []
+    )
+
+  def assertPromiseFails(self, promise):
+    monitor_run_promise = os.path.join(
+      self.computer_partition_root_path, 'software_release', 'bin',
+      'monitor.runpromise'
+    )
+    monitor_configuration = os.path.join(
+      self.computer_partition_root_path, 'etc', 'monitor.conf')
+
+    self.assertNotEqual(
+      0,
+      subprocess.call([
+        monitor_run_promise, '-c', monitor_configuration, '-a', '-f',
+        '--run-only', promise])
+    )
+
+  def test_bad_parameter(self):
+    self.rerequestInstance({
+      'image-url-list': "jsutbad"
+    })
+    self.raising_waitForInstance(3)
+    self.assertPromiseFails('image-url-list-config-state-promise.py')
+
+  def test_incorrect_md5sum(self):
+    self.rerequestInstance({
+      'image-url-list': "%s#" % (self.fake_image,)
+    })
+    self.raising_waitForInstance(3)
+    self.assertPromiseFails('image-url-list-config-state-promise.py')
+    self.rerequestInstance({
+      'image-url-list': "url#asdasd"
+    })
+    self.raising_waitForInstance(3)
+    self.assertPromiseFails('image-url-list-config-state-promise.py')
+
+  def test_not_matching_md5sum(self):
+    self.rerequestInstance({
+      'image-url-list': "%s#%s" % (
+        self.fake_image, self.fake_image_wrong_md5sum)
+    })
+    self.raising_waitForInstance(3)
+    self.assertPromiseFails('image-url-list-download-md5sum-promise.py')
+    self.assertPromiseFails('image-url-list-download-state-promise.py')
+
+  def test_unreachable_host(self):
+    self.rerequestInstance({
+      'image-url-list': "evennotahost#%s" % (
+        self.fake_image_md5sum,)
+    })
+    self.raising_waitForInstance(3)
+    self.assertPromiseFails('image-url-list-download-state-promise.py')
+
+  def test_too_many_images(self):
+    self.rerequestInstance({
+      'image-url-list': """
+      image1#11111111111111111111111111111111
+      image2#22222222222222222222222222222222
+      image3#33333333333333333333333333333333
+      image4#44444444444444444444444444444444
+      image5#55555555555555555555555555555555
+      image6#66666666666666666666666666666666
+      """
+    })
+    self.raising_waitForInstance(3)
+    self.assertPromiseFails('image-url-list-config-state-promise.py')