OCPBUGS-66104: Fine tune CoreDNS pod configuration to improve performance

[sadasu]

Make updates to the Cloud platform CoreDNS Corefile to increase buffersize from 512 to the default of 1232 (by removing the configuration so the default value could take effect).
And prefer UDP for contacting upstream platform upstream DNS servers to reduce load on them.

- What I did

- How to verify it

- Description for the changelog

Summary by CodeRabbit

• Configuration Updates
  • Removed a restrictive DNS UDP buffer setting to allow improved handling of larger responses.
  • Enabled forced TCP for DNS forwarding to improve reliability when responses are truncated.

[openshift-ci-robot]

@sadasu: This pull request references Jira Issue OCPBUGS-66104, which is valid.

3 validation(s) were run on this bug

• bug is open, matching expected state (open)
• bug target version (4.22.0) matches configured target version for branch (4.22.0)
• bug is in the state POST, which is one of the valid states (NEW, ASSIGNED, POST)

Requesting review from QA contact:
/cc @gpei

The bug has been updated to refer to the pull request using the external bug tracker.

Details

In response to this:

Make updates to the Cloud platform CoreDNS Corefile to increase buffersize for 512 to the default of 1232.
And prefer UDP for contacting upstream platform upstream DNS servers to reduce load on them.

- What I did

- How to verify it

- Description for the changelog

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[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: sadasu
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[gpei]

/testwith openshift/installer/master/e2e-aws-custom-dns-techpreview

[sadasu]

/retest-required

[sadasu]

/testwith openshift/installer/master/e2e-aws-custom-dns-techpreview

[sadasu]

/testwith e2e-aws-custom-dns-techpreview

[gpei]

@sadasu seems the command /testwith <installer_pre_submit_job> can't work without an installer PR - https://docs.ci.openshift.org/how-tos/multi-pr-presubmit-testing/#testwith-command, it's requiring the specified test must be defined in a repo to which one of these included PRs belongs.
So I'm running the aws/azure custom-dns e2e job test in openshift/release#73998 separately, but the installations were both failed, will continue the investigating today.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository: openshift/coderabbit/.coderabbit.yaml

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Plan: Pro

Run ID: 07d0f1a4-4801-4679-b7ac-5f5c8fbdcecc

📥 Commits

Reviewing files that changed from the base of the PR and between 86e4155 and 8ddb17b.

📒 Files selected for processing (1)

• templates/common/cloud-platform-alt-dns/files/coredns-corefile.yaml

🚧 Files skipped from review as they are similar to previous changes (1)

• templates/common/cloud-platform-alt-dns/files/coredns-corefile.yaml

---

Walkthrough

CoreDNS Corefile modified: the bufsize 512 directive was removed and force_tcp was added inside the forward block. No other functional changes.

Changes

Cohort / File(s)	Summary
CoreDNS Configuration templates/common/cloud-platform-alt-dns/files/coredns-corefile.yaml	Removed bufsize 512 directive; added force_tcp within the forward block.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title references a Jira bug (OCPBUGS-66104) and mentions CoreDNS pod performance tuning, which aligns with the actual changes to the Corefile configuration for improving DNS performance.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Stable And Deterministic Test Names	✅ Passed	PR modifies only CoreDNS YAML configuration files with no Ginkgo test declarations added or changed.
Test Structure And Quality	✅ Passed	The custom check for Ginkgo test code quality is not applicable to this PR. The PR exclusively modifies a CoreDNS configuration file and contains no test code.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

---

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[openshift-ci-robot]

@sadasu: This pull request references Jira Issue OCPBUGS-66104, which is valid.

3 validation(s) were run on this bug

• bug is open, matching expected state (open)
• bug target version (4.22.0) matches configured target version for branch (4.22.0)
• bug is in the state POST, which is one of the valid states (NEW, ASSIGNED, POST)

No GitHub users were found matching the public email listed for the QA contact in Jira (gpei@redhat.com), skipping review request.

Details

In response to this:

Make updates to the Cloud platform CoreDNS Corefile to increase buffersize from 512 to the default of 1232 (by removing the configuration so the default value could take effect).
And prefer UDP for contacting upstream platform upstream DNS servers to reduce load on them.

- What I did

- How to verify it

- Description for the changelog

Summary by CodeRabbit

Release Notes

• Chores
• Modified DNS configuration to enforce TCP protocol for upstream DNS forwarding
• Updated DNS server list to include an additional resolver for improved redundancy

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the openshift-eng/jira-lifecycle-plugin repository.

[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against the current code and only fix it if needed.

Inline comments:
In `@templates/common/cloud-platform-alt-dns/files/coredns-corefile.yaml`:
- Around line 8-10: In the CoreDNS Corefile inside the forward block (the stanza
starting with "forward . {{`{{- range $upstream := .DNSUpstreams}}
{{$upstream}}{{- end}}`}} {"), remove the force_tcp directive and either replace
it with prefer_udp or omit the line entirely so upstream queries will prefer UDP
and only fall back to TCP on truncation; update the forward block accordingly to
use prefer_udp if you want explicit behavior.

In
`@templates/common/cloud-platform-alt-dns/files/usr-local-bin-update-dns-server.yaml`:
- Line 17: The script hard-codes a public DNS (8.8.8.8) in the servers variable
assignment (servers=$(ip --json route get 8.8.8.8 | jq -r
".[0].prefsrc"),$1,8.8.8.8) which can break private/disconnected installs and
leak queries; change the logic in the servers assignment to stop appending
8.8.8.8 and instead use a configurable fallback or none: read a fallback from an
environment/config variable (e.g., FALLBACK_DNS or platform-provided upstreams)
and only append it when set and allowed, or simply build servers from the local
preferred source and $1 without the hard-coded public resolver.

---

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⚙️ Run configuration

Configuration used: Repository: openshift/coderabbit/.coderabbit.yaml

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Run ID: eea4363e-a62c-4f35-8d64-147cc309dd13

📥 Commits

Reviewing files that changed from the base of the PR and between 7a8a698 and 7281d8e.

📒 Files selected for processing (2)

• templates/common/cloud-platform-alt-dns/files/coredns-corefile.yaml
• templates/common/cloud-platform-alt-dns/files/usr-local-bin-update-dns-server.yaml

[openshift-ci]

@sadasu: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
ci/prow/e2e-gcp-op-ocl	86e4155	link	false	/test e2e-gcp-op-ocl
ci/prow/unit	86e4155	link	true	/test unit

Full PR test history. Your PR dashboard.

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