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---
title: "Proposal: Rollback IPv6 internal Node IP exposure"
version: if applicable
authors: @ivankatliarchuk, @szuecs, @mloiseleur
creation-date: 2025-01-01
status: approved
---

Introduce Feature Flag for IPv6 Internal Node IP Handling in ‘’external-dns’’ and Change the behavior

Summary

This proposal aims to introduce a feature flag in ‘external-dns’ to control the handling of IPv6 internal node IPs.
In the current version, the feature flag will default to the existing behavior. In the next minor or minor+N version, the default behavior will be reversed, encouraging users to adopt the new behavior while providing a transition period.

Motivation

The discussion in issue#4566 and the
subsequent pr#4574 and pr#4808 highlighted concerns regarding the treatment of IPv6 internal node IPs.
To address these concerns without causing immediate disruption, a feature flag will allow users to opt-out the current behavior, providing flexibility during the transition.

Goals

  • Introduce feature to toggle the handling of IPv6 internal node IPs

Non-Goals

  • Propose/Add an annotation for this specific use case
  • Provide support for external-dns.alpha.kubernetes.io/expose-internal-ipv6 in follow-up releases.
  • Managing dual annotation and flag may introduce complexity.

Proposal

  • Introduce Feature Flag
  • Add a feature flag, e.g., --expose-internal-ipv6=true, to control the handling of IPv6 internal node IPs.

  • In the current version, this flag will default to true, maintaining the existing behavior.

  • Flip Default Behavior in Next Minor Version

  • In the subsequent minor release, change the default value of --expose-internal-ipv6 to false, adopting the new behavior by default.
  • Users can still override this behavior by explicitly setting the flag as needed.

Proposed Changes in source/node.go file.

// IPv6 addresses are labeled as NodeInternalIP despite being usable externally as well.
if addr.Type == v1.NodeInternalIP && ns.exposeInternalIP && ... {
    pv6Addresses = append(ipv6Addresses, addr.Address)
}

User Stories

  • As a cluster Operator or Administrator, I want to control the handling of IPv6 internal node IPs to align with defined network topology and configuration.

  • As a SecDevOps, I want to ensure that external-dns does not expose internal IPv6 node addresses via public DNS records, so that I can prevent unintended data leaks and reduce the attack surface of my Kubernetes cluster.

  • As a SecDevOps, I want to use a feature flag to selectively enable or disable the new IPv6 behavior in external-dns, so that I can evaluate its security impact before it becomes the default setting in future releases.

  • As a SecDevOps, I want to use a feature flag to selectively enable or disable the new IPv6 behavior in external-dns, so that I can detect misconfigurations, act on potential security incidents, and ensure compliance with security policies.

Implementation Steps

  • Code Changes:

  • Implement the feature flag in the ‘external-dns’ codebase to toggle the handling of IPv6 internal node IPs.

  • Documentation:

  • Update the ‘external-dns’ documentation to include information about the feature flag, its purpose, and usage examples.

Drawbacks

  • Introducing a feature flag adds complexity to the configuration and codebase.
  • Changing default behavior in a future release may still cause issues for users who are unaware of the change.

Alternatives

  • Immediate Behavior Change
  • Directly change the behavior without a feature flag, which could lead to unexpected issues for users.
  • No Change
  • Maintain the current behavior, potentially leaving the concerns unaddressed.
  • Users may not be able to update an external-dns version due to security, compliance or any other concerns.