feat: add --default-subnets option

[1mwataru]

Issue

close #4046

Description

• Added --default-subnets option
  • When subnets are not explicitly specified through annotations or other methods, the subnets specified in --default-subnets will be selected

Background

• When subnets are not explicitly specified through annotations, subnets are selected in lexicographical order within each availability zone, and the load balancer is created with those subnets. (doc)

• Due to this specification, if there are specific subnets where ELBs should be launched by default, annotations need to be added to all load balancers, which is cumbersome.

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

Manual tests

• Prerequisites

  • AZ a

    • subnet-1a-public
    • subnet-2a-public
    • subnet-1a-private
    • subnet-2a-private

  • AZ b

    • subnet-1b-public
    • subnet-2b-public
    • subnet-1b-private
    • subnet-2b-private

  • AZ c

    • subnet-1c-public
    • subnet-2c-public
    • subnet-1c-private
    • subnet-2c-private

  • Default selection (lexicographical order)

    • Internet facing ELB is created with subnet-1a-public, subnet-1b-public, subnet-1c-public
    • Internal ELB is created with subnet-1a-private, subnet-1b-private, subnet-1c-private

• Pattern 1

  • Specified subnet-2a-public,subnet-2b-public,subnet-2a-private in --default-subnets option
  • result:
    • Internet facing ELB is created with subnet-2a-public,subnet-2b-public,subnet-1c-public
    • Internal ELB is created with subnet-2a-private, subnet-1b-private, subnet-1c-private

• Pattern 2

  • Specified subnet-2a-public,subnet-1a-public in --default-subnets option
  • result:
    • Internet facing ELB is created with subnet-2a-public,subnet-1b-public,subnet-1c-public
    • Internal ELB is created with subnet-1a-private, subnet-1b-private, subnet-1c-private
    • (when two subnets from the same AZ are specified, the first one takes precedence)

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: 1mwataru / name: Wataru (8d6e30a)

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[1mwataru]

Hello, maintainers.

Could you please review this?

Thanks!

[1mwataru]

Hi,

@M00nF1sh, @shraddhabang, @wweiwei-li, @zac-nixon

I looked at the OWNERS and mentioned you.

Could you please take a look at this PR when you have a moment?

If there are any issues in this PR, I'll fix them. Thanks!

[1mwataru]

I have resolved the conflict.

[1mwataru]

I have resolved the conflict :)

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: 1mwataru
Once this PR has been reviewed and has the lgtm label, please assign shraddhabang for approval. For more information see the Code Review Process.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: 1mwataru
Once this PR has been reviewed and has the lgtm label, please assign shraddhabang for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[1mwataru]

Hi,

@M00nF1sh, @oliviassss , @shraddhabang, @wweiwei-li, @zac-nixon

Could you please test and review this? (this is not tested yet by ci workflow).

Thanks!