fix(cassandra): repack exporter with patched Netty

[sbaum1994]

TL;DR

Replace the Cassandra exporter's shaded Netty 4.1.135.Final modules with checksum-pinned Netty 4.1.137.Final artifacts during the image build. This clears the exporter's four fixed Netty advisories without changing the Java agent contract or redistributing its source jar.

Additional Details

• Add a build-only repack stage that replaces the exact eight-module Netty set found in the supplied exporter jar.
• Verify every Maven Central artifact by SHA-256, reject unexpected input module layouts, update scanner-visible Netty metadata, and normalize timestamps for deterministic output.
• Preserve the exporter implementation, Java agent manifest, and unrelated shaded dependencies. Only Netty-owned entries and Netty version declarations change.
• Add a synthetic-jar regression test covering payload preservation, removal of old classes and metadata, the exact replacement module count, and the security version floor.
• This PR is stacked on fix(cassandra): refresh vulnerable runtime dependencies #1611 because that PR updates the same Cassandra runtime image. After fix(cassandra): refresh vulnerable runtime dependencies #1611 merges, this PR can be retargeted to main without changing its exporter-only diff.
• Netty is an existing Apache-2.0 dependency. This updates 4.1.135.Final to 4.1.137.Final, adds no dependency or license, and requires no NOTICE change.

For the Reviewer

Please focus on repack-exporter-netty.sh: its module-set guard and path filters are the controls that prevent a partial or over-broad fat-jar rewrite.

For QA

• infra/cassandra/scripts/repack-exporter-netty-test.sh
• shellcheck infra/cassandra/scripts/repack-exporter-netty.sh infra/cassandra/scripts/repack-exporter-netty-test.sh
• Repacked the release exporter twice; both outputs had SHA-256 d4495c8d19f58f8da56a0c40cb8605062c2fb2e7c336cdfa8be29470a0016608.
• Compared the real input and output jars; every non-Netty entry and the Java agent manifest were byte-identical, with only Netty version declarations normalized in the exporter POM metadata.
• Built the real exporter overlay for linux/amd64 and linux/arm64 with docker buildx build.
• Ran io.netty.util.Version in the built image; all eight embedded modules reported 4.1.137.Final.
• Started Cassandra from the built image and fetched live Prometheus metrics from port 9500.

No additional QA is required beyond the image build and existing Cassandra validation.

Issues

Closes #1606

Checklist

• I am familiar with the Contributing Guidelines.
• I have signed off my commits for Developer Certificate of Origin (DCO) compliance.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

Summary by CodeRabbit

• Improvements

  • Cassandra exporter images now use checksum-verified Netty 4.1.137.Final modules.
  • Exporter packaging preserves application content and metadata while replacing bundled Netty components.
  • Builds validate exporter archive structure and fail when unexpected Netty modules or layouts are detected.

• Documentation

  • Added guidance for providing required metrics build arguments together and configuring exporter repackaging.

• Tests

  • Added coverage for module replacement, metadata updates, archive validation, and preservation of exporter contents.

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• infra/cassandra/AGENTS.md
• infra/cassandra/Dockerfile
• infra/cassandra/README.md

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• infra/cassandra/AGENTS.md

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📝 Walkthrough

Walkthrough

The Cassandra exporter build now repacks its JAR with checksum-pinned Netty 4.1.137.Final modules. The build validates input and output layouts, preserves exporter content, and uses the repacked artifact in the final image.

Changes

Cassandra exporter Netty replacement

Layer / File(s)	Summary
Pinned Netty repackaging infra/cassandra/scripts/repack-exporter-netty.sh	Adds checksum verification, input layout validation, Netty replacement, metadata rewriting, completeness checks, and reproducible archive creation.
Repackaging validation infra/cassandra/scripts/repack-exporter-netty-test.sh, infra/cassandra/AGENTS.md	Adds a synthetic JAR test that verifies preserved exporter content, replacement Netty classes, eight modules, and pinned metadata. Documents the dependency test command.
Docker build integration and documentation infra/cassandra/Dockerfile, infra/cassandra/README.md, infra/cassandra/AGENTS.md	Adds the repacker build stage, copies the repacked agent into the final image, and documents build arguments and replacement behavior.

Estimated code review effort: 4 (Complex) | ~45 minutes

Merge Risk: ⚪ Minimal · up to 527fb

The Cassandra exporter image now embeds the patched Netty modules through a validated, deterministic repack step while preserving the agent payload and manifest. No concrete current-head merge-blocking risk remains.

Sequence Diagram(s)

sequenceDiagram
  participant DockerBuild
  participant RepackScript
  participant MavenCentral
  DockerBuild->>RepackScript: Invoke repack-exporter-netty.sh with exporter JAR
  RepackScript->>MavenCentral: Download checksum-pinned Netty modules
  MavenCentral-->>RepackScript: Return Netty artifacts
  RepackScript-->>DockerBuild: Copy validated repacked exporter JAR into final image

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🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (3 skipped: 3 …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title uses valid Conventional Commits syntax, includes the required cassandra scope for a fix, and accurately describes the Netty repacking change.
Linked Issues check	✅ Passed	The changes satisfy issue #1606 by repacking the exporter with Netty 4.1.137.Final, verifying checksums, rejecting unexpected module layouts, removing the affected version, preserving the exporter and…
Out of Scope Changes check	✅ Passed	All changes are directly related to rebuilding the Cassandra exporter with patched Netty. The documentation, repacking script, build-stage changes, and regression test support the linked issue objecti…

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 2 files. (3 skipped: 3 unsupported.)

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/cassandra-exporter-netty-1606

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[sbaum1994]

Risk assessment: Medium

Component delta:

• Exporter-shaded Netty modules: 4.1.135.Final to 4.1.137.Final for buffer, codec, codec-http, common, handler, resolver, transport, and transport-native-unix-common.
• Exporter implementation: unchanged.
• Java agent manifest and unrelated shaded dependencies: unchanged.
• No API, chart, data-model, or metrics-contract change. Supported build modes are unchanged; mismatched exporter arguments now fail at build time.

Change size and nature:

• The exporter-only diff adds one build stage, a fail-closed argument-pair guard, a 180-line repack script, an 89-line regression test, and small documentation updates.
• The script downloads the exact eight replacement jars with pinned SHA-256 values, replaces only Netty-owned jar entries, updates Netty version declarations, and produces deterministic output.
• This PR is stacked on fix(cassandra): refresh vulnerable runtime dependencies #1611. That base PR has its own Cassandra runtime dependency updates; this assessment covers only the exporter delta shown against fix/1605-cassandra-runtime.

Primary risks and mitigations:

• Netty binary compatibility: the update stays within the 4.1 patch line. The actual combined image started Cassandra successfully and served the existing Prometheus metrics endpoint.
• Partial fat-jar replacement: the build rejects any input whose embedded Netty module set differs from the pinned eight modules, then verifies every output module reports 4.1.137.Final.
• Supply-chain availability or tampering: Maven Central download or checksum failure stops the build before an image is produced.
• Build-argument compatibility: established builds that pass both exporter arguments, or neither argument, are unchanged. Either one-argument combination now fails early instead of producing an image with disabled metrics or an invalid Java agent.
• Base/exporter classpath interaction: fix(cassandra): refresh vulnerable runtime dependencies #1611 supplies Cassandra's standalone Netty 4.1.136.Final jars while the exporter contains 4.1.137.Final. The live smoke used that exact combination and exercised exporter collection through port 9500.

Rollback is a single commit revert, but doing so restores the affected 4.1.135.Final exporter payload. A new Cassandra image release and vulnerability scan are required to confirm production closure.

[sbaum1994]

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Actionable comments posted: 1

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Inline comments:
In `@infra/cassandra/AGENTS.md`:
- Line 20: Correct the argument-behavior statement in AGENTS.md: document that
only EXPORTER_JAR alone runs without metrics, while EXPORTER_JAVAAGENT alone is
invalid because it causes the empty placeholder to be loaded as a Java agent;
alternatively, update the build validation to reject mismatched arguments.

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📒 Files selected for processing (5)

• infra/cassandra/AGENTS.md
• infra/cassandra/Dockerfile
• infra/cassandra/README.md
• infra/cassandra/scripts/repack-exporter-netty-test.sh
• infra/cassandra/scripts/repack-exporter-netty.sh

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[sbaum1994]

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