v1beta1 -> v1beta2 migration tool

[fabriziopandini]

What would you like to be added (User Story)?

As a user I would like something helping me in the migration v1beta1 -> v1beta2

Detailed Description

It could be useful to add to clusterctl an alpha command performing v1beta1 -> v1beta2 migration of a given input file (reads a file/reads from stdin, call conversions for all the objects in the file, prints the output to stdout).

Anything else you would like to add?

Some limitation applies:

• Only core CAPI resources can be migrated
• Migration will be "mechanical", calling top level conversion func without any additional context
• Output will be serialized using standard yaml librearies, and this implies loosing comments or changing fields order
• API version for references will be dropped in most cases (as expected) with a few notable exceptions like external remediation and cluster class references
• ClusterClass patches will not me migrated (same as cluster class references)

Those limitation should be documented in the command help

Label(s) to be applied

/kind feature
One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels.

[sbueringer]

/triage accepted

[fabriziopandini]

/help

[k8s-ci-robot]

@fabriziopandini:
This request has been marked as needing help from a contributor.

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[ramessesii2]

/assign

[ramessesii2]

Here's the proposed command for this cli feature-
clusterctl alpha migrate [SOURCE] where SOURCE: optional path to a manifest; defaults to - (stdin) when omitted.

Keeping migrate under the existing alpha command tree.

Flags

--output, -o: path for migrated YAML; defaults to stdout.
-h, --help - show help

Proposed Behavior

• Process all resources in the input
• Convert supported CAPI v1beta1 resources to v1beta2
• Pass through unsupported/non-CAPI resources unchanged
• Write warnings to stderr for any issues
• Always output results to stdout (or --output file)
• Exit code 0 for success, non-zero if critical errors