Interoperable Image Import

updated: 2019-09-10 15:48

Interoperable Image Import¶

Version 2.6 of the Image Service API introduces new API calls that implement an interoperable image import process. These API calls, and the workflow for using them, are described in the Interoperable Image Import section of the Image Service API reference. That documentation explains the end user’s view of interoperable image import. In this section, we discuss what configuration options are available to operators.

The interoperable image import process uses Glance tasks, but does not require that the Tasks API be exposed to end users. Further, it requires the taskflow task executor. The following configuration options must be set:

in the [task] option group:
- task_executor must either be set to taskflow or be used in its default value
in the [taskflow_executor] options group:
- The default values are fine. It’s a good idea to read through the descriptions in the sample glance-api.conf file to see what options are available.
  
  Note
  
  You can find an example glance-api.conf file in the etc/ subdirectory of the Glance source code tree. Make sure that you are looking in the correct branch for the OpenStack release you are working with.
in the default options group:
- enable_image_import must be either absent or set to True (the default).
  
  Note
  
  In the Pike release, the default value for this option was False. This option is DEPRECATED and will be removed in the Rocky release.
  
  If enable_image_import is set False, requests to the v2 endpoint for URIs defined only in v2.6 will return 404 (Not Found) with a message in the response body stating “Image import is not supported at this site.” Additionally, the image-create response will not contain the “OpenStack-image-import-methods” header.
- node_staging_uri must specify a location writable by the glance user. If you have multiple Glance API nodes, this should be a reference to a shared filesystem available to all the nodes.
- enabled_import_methods must specify the import methods you are exposing at your installation. The default value for this setting is ['glance-direct','web-download']. See the next section for a description of these import methods.

Additionally, your policies must be such that an ordinary end user can manipulate tasks. In releases prior to Pike, we recommended that the task-related policies be admin-only so that end users could not access the Tasks API. In Pike, a new policy was introduced that controls access to the Tasks API. Thus it is now possible to keep the individual task policies unrestricted while not exposing the Tasks API to end users. Thus, the following is the recommended configuration for the task-related policies:

"get_task": "",
"get_tasks": "",
"add_task": "",
"modify_task": "",
"tasks_api_access": "role:admin",

Image Import Methods¶

Glance provides two import methods that you can make available to your users: glance-direct and web-download. By default, both methods are enabled.

The glance-direct import method allows your users to upload image data directly to Glance.
The web-download method allows an end user to import an image from a remote URL. The image data is retrieved from the URL and stored in the Glance backend. (In other words, this is a copy-from operation.)

Note

The web-download import method replaces the copy-from functionality that was available in the Image API v1 but previously absent from v2. This note is a gentle reminder that the Image API v1 is DEPRECATED and will be removed from Glance during the Rocky development cycle. The Queens release of Glance (16.x.x) is the final version in which you can expect to find the Image API v1.

You control which methods are available to API users by the enabled_import_methods configuration option in the default section of the glance-api.conf file.

Configuring the glance-direct method¶

For the glance-direct method, make sure that glance-direct is included in the list specified by your enabled_import_methods setting, and that all the options described above are set properly.

Configuring the web-download method¶

To enable the web-download import method, make sure that it is included in the list of methods in the enabled_import_methods option, and that all the options described above are set properly.

Note

You must configure the node_staging_uri for the web-download import method because that is where Glance will store the downloaded content. This gives you the opportunity to have the image data be processed by the same plugin chain for each of the import methods. See Customizing the image import process for more information.

Additionally, you have the following configuration available.

Depending on the nature of your cloud and the sophistication of your users, you may wish to restrict what URIs they may use for the web-download import method.

Note

You should be aware of OSSN-0078, “copy_from in Image Service API v1 allows network port scan”. The v1 copy_from feature does not have the configurability described here.

You can do this by configuring options in the [import_filtering_opts] section of the glance-image-import.conf file.

Note

The glance-image-import.conf is an optional file. (See below for a discussion of the default settings if you don’t include this file.)

You can find an example file named glance-image-import.conf.sample in the etc/ subdirectory of the Glance source code tree. Make sure that you are looking in the correct branch for the OpenStack release you are working with.

You can whitelist (“allow only these”) or blacklist (“do not allow these”) at three levels:

scheme (allowed_schemes, disallowed_schemes)
host (allowed_hosts, disallowed_hosts)
port (allowed_ports, disallowed_ports)

There are six configuration options, but the way it works is that if you specify both at any level, the whitelist is honored and the blacklist is ignored. (So why have both? Well, you may want to whitelist a scheme, but blacklist a host, and whitelist a particular port.)

Validation of a URI happens as follows:

The scheme is checked.
1. missing scheme: reject
2. If there’s a whitelist, and the scheme is not in it: reject. Otherwise, skip c and continue on to 2.
3. If there’s a blacklist, and the scheme is in it: reject.
The hostname is checked.
1. missing hostname: reject
2. If there’s a whitelist, and the host is not in it: reject. Otherwise, skip c and continue on to 3.
3. If there’s a blacklist, and the host is in it: reject.
If there’s a port in the URI, the port is checked.
1. If there’s a whitelist, and the port is not in it: reject. Otherwise, skip b and continue on to 4.
2. If there’s a blacklist, and the port is in it: reject.
The URI is accepted as valid.

Note that if you allow a scheme, either by whitelisting it or by not blacklisting it, any URI that uses the default port for that scheme by not including a port in the URI is allowed. If it does include a port in the URI, the URI will be validated according to the above rules.

Default settings¶

The glance-image-import.conf is an optional file. Here are the default settings for these options:

allowed_schemes - ['http', 'https']
disallowed_schemes - empty list
allowed_hosts - empty list
disallowed_hosts - empty list
allowed_ports - [80, 443]
disallowed_ports - empty list

Thus if you use the defaults, end users will only be able to access URIs using the http or https scheme. The only ports users will be able to specify are 80 and 443. (Users do not have to specify a port, but if they do, it must be either 80 or 443.)

Note

The glance-image-import.conf is an optional file. You can find an example file named glance-image-import.conf.sample in the etc/ subdirectory of the Glance source code tree. Make sure that you are looking in the correct branch for the OpenStack release you are working with.

Customizing the image import process¶

When a user issues the image-import call, Glance retrieves the staged image data, processes it, and saves the result in the backing store. You can customize the nature of this processing by using plugins. Some plugins are provided by the Glance project team, you can use third-party plugins, or you can write your own.

Technical information¶

The import step of interoperable image import is performed by a Taskflow “flow” object. This object, provided by Glance, will call any plugins you have specified in the glance-image-import.conf file. The plugins are loaded by Stevedore and must be listed in the entry point registry in the namespace glance.image_import.plugins. (If you are using only plugins provided by the Glance project team, these are already registered for you.)

A plugin must be written in Python as a Taskflow “Task” object. The file containing this object must be present in the glance/async/flows/plugins directory. The plugin file must contain a get_flow function that returns a Taskflow Task object wrapped in a linear flow. See the no_op plugin, located at glance/async/flows/plugins/no_op.py for an example of how to do this.

Specifying the plugins to be used¶

First, the plugin code must exist in the directory glance/async/flows/plugins. The name of a plugin is the filename (without extension) of the file containing the plugin code. For example, a file named fred_mertz.py would contain the plugin fred_mertz.

Second, the plugin must be listed in the entry point list for the glance.image_import.plugins namespace. (If you are using only plugins provided with Glance, this will have already been done for you, but it never hurts to check.) The entry point list is in setup.cfg. Find the section with the heading [entry_points] and look for the line beginning with glance.image_import.plugins =. It will be followed by a series of lines of the form:

<plugin-name> = <module-package-name>:get_flow

For example:

no_op = glance.async.flows.plugins.no_op:get_flow

Make sure any plugin you want to use is included here.

Third, the plugin must be listed in the glance-image-import.conf file as one of the plugin names in the list providing the value for the image_import_plugins option. Plugins are executed in the order they are specified in this list.

The Image Property Injection Plugin¶

release introduced	Queens (Glance 16.0.0)
configuration file	`glance-image-import.conf`
configuration file section	`[inject_metadata_properties]`

This plugin implements the Glance spec Inject metadata properties automatically to non-admin images. One use case for this plugin is a situation where an operator wants to put specific metadata on images imported by end users so that virtual machines booted from these images will be located on specific compute nodes. Since it’s unlikely that an end user (the image owner) will know the appropriate properties or values, an operator may use this plugin to inject the properties automatically upon image import.

Note

This plugin may only be used as part of the interoperable image import workflow (POST v2/images/{image_id}/import). It has no effect on the image data upload call (PUT v2/images/{image_id}/file).

You can guarantee that your end users must use interoperable image import by restricting the upload_image policy appropriately in the Glance policy.json file. By default, this policy is unrestricted (that is, any authorized user may make the image upload call).

For example, to allow only admin or service users to make the image upload call, the policy could be restricted as follows:

"upload_image": "role:admin or (service_user_id:<uuid of nova user>) or
   (service_roles:<service user role>)"

where “service_role” is the role which is created for the service user and assigned to trusted services.

To use the Image Property Injection Plugin, the following configuration is required.

You will need to configure ‘glance-image-import.conf’ file as shown below:
```
[image_import_opts]
image_import_plugins = [inject_image_metadata]

[inject_metadata_properties]
ignore_user_roles = admin,...
inject = "property1":"value1","property2":"value2",...
```
The first section, image_import_opts, is used to enable the plugin by specifying the plugin name as one of the elements of the list that is the value of the image_import_plugins parameter. The plugin name is simply the module name under glance/async/flows/plugins/

The second section, inject_metadata_properties, is where you set the parameters for the injection plugin. (Note that the values you specify here only have an effect if the plugin has been enabled in the image_import_plugins list as described above.)
- ignore_user_roles is a comma-separated list of Keystone roles that the plugin will ignore. In other words, if the user making the image import call has any of these roles, the plugin will not inject any properties into the image.
- inject is a comma-separated list of properties and values that will be injected into the image record for the imported image. Each property and value should be quoted and separated by a colon (‘:’) as shown in the example above.
If your use case is such that you don’t want to allow end-users to create, modify, or delete metadata properties that you are injecting during the interoperable image import process, you will need to protect these properties using the Glance property protection feature (available since the Havana release).

For example, suppose there is a property named ‘property1’ that you want injected during import, but you only want an administrator or service user to be able to create this property, and you want only an administrator to be able to modify or delete it. You could accomplish this by adding the following to the property protection configuration file:
```
[property1]
create = admin,service_role
read = admin,service_role,member,_member_
update = admin
delete = admin
```
See the Property Protections section of this Guide for more information.

updated: 2019-09-10 15:48

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