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kubernetes/migration: support simple downgrade cases (#172)

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* support basic downgrades

* add unit test for validDownMigration

* add no-op test for downward migration

* document
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Chris O'Haver 2019-05-20 16:11:03 -04:00 • committed by GitHub
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13
kubernetes/migration/README.md
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@ -30,15 +30,22 @@ any new default plugins that would be added in a migration. Notices
`Migrate(fromCoreDNSVersion, toCoreDNSVersion, corefileStr string, deprecations bool) (string, error)`
Migrate returns a migrated version of the Corefile, or an error if it cannot. It will:
Migrate returns a migrated version of the Corefile, or an error if it cannot. The _to_ version
must be >= the _from_ version. It will:
* replace/convert any plugins/options that have replacements (e.g. _proxy_ -> _forward_)
* return an error if replacable plugins/options cannot be converted (e.g. proxy _options_ not available in _forward_)
* remove plugins/options that do not have replacements (e.g. kubernetes `upstream`)
* add in any new default plugins where applicable if they are not already present (e.g. adding _loop_ plugin when it was added).
This will have to be case by case, and could potentially get complicated.
* add in any new default plugins where applicable if they are not already present.
* If deprecations is true, deprecated plugins/options will be migrated as soon as they are deprecated.
* If deprecations is false, deprecated plugins/options will be migrated only once they become removed or ignored.
`MigrateDown(fromCoreDNSVersion, toCoreDNSVersion, corefileStr string) (string, error)`
MigrateDown returns a downward migrated version of the Corefile, or an error if it cannot. The _to_ version
must be <= the _from_ version.
* It will handle the removal of plugins and options that no longer exist in the destination
version when downgrading.
* It will not restore plugins/options that might have been removed or altered during an upward migration.
`Unsupported(fromCoreDNSVersion, toCoreDNSVersion, corefileStr string) ([]Notice, error)`