Add exact match check to use specified addon versions

[aoshi2000]

Add exact match check to use specified addon versions

Description

The current addon version selection logic uses partial string matching to find the latest version among all matching candidates. This causes unexpected behavior when users specify exact versions.

For example, when a user runs:

eksctl update addon --cluster my-cluster --name coredns --version v1.0.0-eksbuild.2

The current implementation incorrectly selects v1.0.0-eksbuild.20 instead of the specified v1.0.0-eksbuild.2 , because strings.Contains("v1.0.0-eksbuild.20", "v1.0.0-eksbuild.2") returns true.

This Pull Request adds an exact match check before the partial matching logic in getLatestMatchingVersion().

Manual Test Results

before

eksctl update addon --name coredns --version v1.11.4-eksbuild.1 --cluster <cluster-name> --force
2025-08-24 10:29:50 [!]  no IAM OIDC provider associated with cluster, try 'eksctl utils associate-iam-oidc-provider --region=ap-northeast-1 --cluster=<cluster-name>'
2025-08-24 10:29:50 [ℹ]  Kubernetes version "1.33" in use by cluster "<cluster-name>"
2025-08-24 10:29:50 [ℹ]  new version provided v1.11.4-eksbuild.14
2025-08-24 10:29:50 [ℹ]  updating addon

after

./eksctl update addon --name coredns --version v1.11.4-eksbuild.1 --cluster <cluster-name> --force
2025-08-24 10:27:27 [!]  no IAM OIDC provider associated with cluster, try 'eksctl utils associate-iam-oidc-provider --region=ap-northeast-1 --cluster=<cluster-name>'
2025-08-24 10:27:27 [ℹ]  Kubernetes version "1.33" in use by cluster "<cluster-name>"
2025-08-24 10:27:28 [ℹ]  new version provided v1.11.4-eksbuild.1
2025-08-24 10:27:28 [ℹ]  updating addon

Checklist

• Added tests that cover your change (if possible)
• Added/modified documentation as required (such as the README.md, or the userdocs directory)
  => I think no documentation changes are required as the modified behavior aligns with existing documentation expectations.

The addon version can be set to latest. Alternatively, the version can be set with the EKS build tag specified, such as v1.7.5-eksbuild.1 or v1.7.5-eksbuild.2. It can also be set to the release version of the addon, such as v1.7.5 or 1.7.5, and the eksbuild suffix tag will be discovered and set for you.

https://eksctl.io/usage/addons/

• Manually tested
• Made sure the title of the PR is a good description that can go into the release notes
• (Core team) Added labels for change area (e.g. area/nodegroup) and kind (e.g. kind/improvement)

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 🌟

[github-actions]

Hello aoshi2000 👋 Thank you for opening a Pull Request in eksctl project. The team will review the Pull Request and aim to respond within 1-10 business days. Meanwhile, please read about the Contribution and Code of Conduct guidelines here. You can find out more information about eksctl on our website

[sapphirew]

LGTM. Thanks for submitting this fix!