Add spec for Image Introspection blueprint
Related blueprint: introspection-of-images Change-Id: Iab766b2fff5ff08b06ce02a09ca03553e27f0cb2
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Ian Cordasco
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This work is licensed under a Creative Commons Attribution 3.0 Unported
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License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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===========================
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Introspection of Images
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===========================
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https://blueprints.launchpad.net/glance/+spec/introspection-of-images
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Several image formats include metadata inside the image data. This spec
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proposes that Glance expose that metadata through introspection of the image.
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For example, we can read the metadata from a ``vmdk`` formatted image to know
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that the disk type of the image is "streamOptimized". Allowing Glance to
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perform the introspection removes the burden from the administrator. Exposing
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this metadata also helps the consumer of the image; Nova's workflow is very
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different based on the disk type of the image.
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Problem description
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===================
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Several image formats include metadata inside the image data. A stream
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optimized ``vmdk`` image could be introspected like so:
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.. code::
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$ head -20 so-disk.vmdk
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# Disk DescriptorFile
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version=1
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CID=d5a0bce5
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parentCID=ffffffff
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createType="streamOptimized"
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# Extent description
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RDONLY 209714 SPARSE "generated-stream.vmdk"
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# The Disk Data Base
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#DDB
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ddb.adapterType = "buslogic"
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ddb.geometry.cylinders = "102"
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ddb.geometry.heads = "64"
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ddb.geometry.sectors = "32"
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ddb.virtualHWVersion = "4"
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When a user of the image looks at the metadata they will see important
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information like the required disk type, "streamOptimized". Extracting the
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metadata in Glance and exposing it through Glance's API, means that
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administrators and image users alike do not need to perform the introspection
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themselves. Consumers like Nova will have very different workflows based on
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disk type alone and could also optimize the rest of its workflow based on
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other image metadata.
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Proposed change
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===============
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Using `Glance's Asynchronous Workers`_, we can extract the image metadata
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without requiring a separate node and without suffering significant
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performance degradation.
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.. _Glance's Asynchronous Workers:
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https://blueprints.launchpad.net/glance/+spec/async-glance-workers
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Alternatives
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------------
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A separate worker node could ostensibly be controlled to prevent degradation
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on the Glance API nodes but is an unnecessary addition to the architecture.
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Data model impact
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-----------------
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None
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REST API impact
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---------------
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None
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Security impact
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---------------
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None
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Notifications impact
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--------------------
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None
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Other end user impact
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---------------------
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None
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Performance Impact
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------------------
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Based on the maximum number of workers and the size that the administrator has
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configured for the introspection workspace, performance could be negatively
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affected if the operator misconfigures their maximum number of workers and
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allocated workspace.
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Other deployer impact
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---------------------
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When configuring this feature, operators will need to know the average size of
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the images that they are managing and appropriately configure the
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``max_workers`` setting and an appropriate amount of space for the workers to
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use.
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Developer impact
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----------------
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None
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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flaper87
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Other contributors:
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jokke\_
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Reviewers
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---------
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Core reviewer(s):
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nikhil-komawar
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kragniz
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icordasc
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Work Items
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----------
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- Create specific workers for different introspection tasks
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- Create workflows for tasks
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- Update configuration files with additions
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- Update configuration documentation
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Dependencies
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============
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This depends on `Glance's Asynchronous Workers`_.
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Testing
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=======
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Unit testing will be needed for the introspection tasks and for the new task
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flows.
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Documentation Impact
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====================
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This may have an impact on the upgrade and installation parts of the
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documentation. For operators upgrading, they'll need to understand how to
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properly configure a system for image introspection. For new users, they'll
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need to be warned about appropriately allocating space for the workers to use
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and possibly choosing a more conservative maximum worker number than is
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default until they can determine the appropriate number.
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References
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==========
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None
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