Add spec for the removal of Swift from the Undercloud
This spec has been submitted to enable us to remove Swift from the Undercloud. The Spec is a highlevel document which provides insight into the process we believe we can take to excise swift from the Undercloud. Change-Id: I7890f87acfb9d5aab47ee943ab85364d309867cb Signed-off-by: Kevin Carter <kecarter@redhat.com>
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Kevin Carter
Kevin Carter (cloudnull)
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specs/wallaby/excise-swift.rst
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specs/wallaby/excise-swift.rst
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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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Disable Swift from the Undercloud
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=================================
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The goal of this proposal is to introduce the community to the idea of
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disabling Swift on the TripleO Undercloud. Within this propose we intend
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to provide a high-level overview of how we can accomplish this goal.
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Problem Description
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===================
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Swift is being used to store objects related to the deployment which are
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managed entirely on the Undercloud. In the past, there was an API / UI to
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interact with the deployment tooling; however, with the deprecation of the UI
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and the removal of Mistral this is no longer the case. The Undercloud is
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assumed to be a single node which is used to deploy OpenStack clouds, and
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requires the user to login to the node to run commands. Because we're no longer
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attempting to make the Undercloud a distributed system there's no need for an
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API'able distributed storage service. Swift, in it's current state, is
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under-utilized and carries unnecessary operational and resource overhead.
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Proposed Change
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===============
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Overview
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--------
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Decommission Swift from the Undercloud.
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To decommission Swift, we'll start by removing all of the `tripleoclient` Swift
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interactions. These interactions are largely storing and retrieving YAML files
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which provide context to the user for current deployment status. To ensure
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we're not breaking deployment expectations, we'll push everything to the local
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file system and retain all of the file properties wherever possible. We will
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need coordinate with tripleo-ansible to ensure we're making all direct Swift
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client and module interactions optional.
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Once we're able to remove the `tripleoclient` Swift interactions, we'll move to
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disable Swift interactions from tripleo-common. These interactions are similar
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to the ones found within the `tripleoclient`, though tripleo-common has some
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complexity; we'll need to ensure we're not breaking expectations we've created
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with our puppet deployment methodologies which have some Swift assumptions.
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Alternatives
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------------
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We keep everything as-is.
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Security Impact
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---------------
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There should be no significant security implications when disabling Swift.
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It could be argued that disabling Swift might make the deployment more secure,
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it will lessen the attack surface; however, given the fact that Swift on the
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Undercloud is only used by director I would consider any benefit insignificant.
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Upgrade Impact
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--------------
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There will be no upgrade impact; this change will be transparent to the
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end-user.
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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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Disabling Swift could make some client interactions faster; however, the
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benefit should be negligible. That said, disabling Swift would remove a
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service on the Undercloud, which would make setup faster and reduce the
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resources required to run the Undercloud.
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Other Deployer Impact
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---------------------
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Operationally we should see an improvement as it will no longer be required to
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explore a Swift container, and download files to debug different parts of the
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deployment. All deployment related file artifacts housed within Swift will
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exist on the Undercloud using the local file system, and should be easily
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interacted with.
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Developer Impact
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----------------
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None, if anything disabling Swift should make the life of a TripleO developer
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easier.
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Implementation
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==============
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Excising Swift client interactions will be handled directly in as few reviews
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as possible; hopefully allowing us to backport this change, should it be deemed
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valuable to stable releases.
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All of the objects stored within Swift will be stored in
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`/var/lib/tripleo/{named_artifact_directories}`. This will allow us to
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implement all of the same core logic in our various libraries just without the
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use of the API call to store the object.
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In terms of enabling us to eliminate swift without having a significant impact
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on the internal API we'll first start by trying to replace the swift object
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functions within tripleo-common with local file system calls. By using the
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existing functions and replacing the backend we'll ensure API compatibility and
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lessen the likely hood of creating regressions.
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.. note::
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We'll need to collaborate with various groups to ensure we're porting assumed
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functionality correctly. While this spec will not go into the specifics
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implementation details for porting assumed functionality, it should be known
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that we will be accountable for ensuring existing functionality is ported
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appropriately.
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Assignee(s)
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-----------
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Primary assignee:
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cloudnull
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Other contributors:
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- emilien
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- ekultails
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Work Items
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----------
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The work items listed here are high level, and not meant to provide specific
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implementation details or timelines.
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* Enumerate all of the Swift interactions
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* Create a space on the Undercloud to house the files
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* This location will be on the local file system and will be created into a
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git archive; git is used for easier debug, rapid rollback, and will
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provide simple versioning.
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* Create an option to disable Swift on the Undercloud.
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* Convert client interactions to using the local file system
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* Ensure all tripleo-ansible Swift client calls are made optional
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* Convert tripleo-common Swift interactions to using the local file system
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* Disable Swift on the Undercloud
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Dependencies
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============
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Before Swift can be disabled on the Undercloud we will need ensure the
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deployment methodology has been changed to Metalsmith.
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Testing
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=======
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The Swift tests will need to be updated to use the local file system, however
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the existing tests and test structure will be reused.
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Documentation Impact
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====================
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There are several references to Swift in our documentation which we will need to
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update.
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References
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==========
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* https://etherpad.opendev.org/p/tripleo-heat-swift-removal-undercloud
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* http://paste.openstack.org/show/798208
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