feat(aws): add ApplyFamilyNUSizingRDSWithExpiry for rebuy-window RDS sizing

[cristim]

Summary by CodeRabbit

• New Features
  • Added expiry-aware sizing for RDS reservation family coverage. Reservations expiring within a specified rebuy window are accounted for when calculating coverage.
  • Reports the total reservation units deducted from coverage and the number of expiring reservations that could not be used in the calculation.
  • Existing RDS family sizing remains available without expiry adjustments.

[cristim]

Cross-link: LeanerCloud/cloud-commitments-cli#2132 (CLI fix follows after this merges and the pin is bumped).

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📥 Commits

Reviewing files that changed from the base of the PR and between 648e1c5 and 707ca12.

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📒 Files selected for processing (3)

• CHANGELOG.md
• providers/aws/recommendations/family_nu.go
• providers/aws/recommendations/family_nu_expiry_test.go

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📝 Walkthrough

📝 Walkthrough

Walkthrough

The change adds ApplyFamilyNUSizingRDSWithExpiry and FamilyExpiryReport. The new entry point adjusts RDS family coverage for eligible reservations expiring within a positive-day window, then applies family sizing. The existing sizing entry point uses a shared sizing helper.

Changes

RDS family expiry sizing

Layer / File(s)	Summary
Shared family sizing providers/aws/recommendations/family_nu.go	ApplyFamilyNUSizingRDS now delegates family grouping and sizing to sizeRDSFamilies, which accepts aggregated coverage.
Expiry-aware sizing and validation providers/aws/recommendations/family_nu.go, providers/aws/recommendations/family_nu_expiry_test.go, CHANGELOG.md	The new entry point adjusts family coverage for eligible expiring commitments and reports deducted normalized units and unusable commitments. Tests cover expiry-window cases, linked-account rows, usage caps, mixed sizes, and invalid targets. The changelog documents the new entry point.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Change: Feature

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Merge Risk: 🟡 Moderate · up to 648e1

The new expiry-aware RDS sizing can undercount rebuy recommendations when non-reservation commitments are present or when engines without size flexibility are involved. Its report can also overstate the deducted units. Existing sizing behavior is unaffected, but these issues should be resolved before the CLI starts relying on the new function.

Pre-merge checks | 4 | 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 63.64% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 2 files. (1 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly identifies the new ApplyFamilyNUSizingRDSWithExpiry function and its rebuy-window RDS sizing purpose. It matches the main change.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

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Full details: Docstring Coverage

Explanation

Docstring coverage is 63.64% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 11 functions across 2 files. (1 skipped: 1 unsupported.)

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[coderabbitai]

Actionable comments posted: 3

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• 🪄 Fix CodeRabbit comments on this PR

🤖 Prompt to fix review comments

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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
minimal, and validate.

Inline comments:
Review comments at @providers/aws/recommendations/family_nu.go:
- Line 457: Update rdsCommitmentFamilyUnits to require c.CommitmentType to equal
common.CommitmentReservedInstance in addition to its existing service and
active-commitment checks. Set expiryTestRI.CommitmentType to
common.CommitmentReservedInstance so the expiry test exercises the intended
commitment type.
- Line 447: Update the `ExpiringNU` accumulation near `CoveredNU` adjustment to
add only the amount actually deducted from `CoveredNU`, calculated as its value
before adjustment minus its value afterward. In the excess-reservation test,
assert that `ExpiringNU` is zero when no covered usage is deducted.
- Line 445: Update the coverage adjustment around `fc.CoveredNU` so RDS SQL
Server and Oracle License Included reservations are not counted across instance
sizes; use size-specific commitments for those engines, or skip this
family-level adjustment for them until size-specific coverage is available.

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📥 Commits

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📒 Files selected for processing (3)

• CHANGELOG.md
• providers/aws/recommendations/family_nu.go
• providers/aws/recommendations/family_nu_expiry_test.go

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[cristim]

Independent merge-gate review (Opus 5.5, claude-opus-5-5): CHANGES REQUESTED

Reviewed SHA: 648e1c5be57f617fc3d604825961a41cd7836d6f (base origin/main 9dae64b, branch up to date). Not merged.

Blocking findings

F1 (money path, over-purchase): the min(CoveredNU, activeNU - expiringNU) clamp deducts more than the expiring NU when the commitment list is incomplete.
family_nu.go:445. activeNU is built only from the commitments the caller supplies, while CoveredNU comes from org-wide Cost Explorer coverage (pool keys carry no account). The CLI's rebuy inventory today is one GetExistingCommitments call for the selected account (cli#2131), so RIs owned by other accounts that cover the same family are missing from activeNU. Whenever activeNU < CoveredNU, the clamp removes coverage that no supplied RI accounts for.

Reproduced at this SHA (scratch test, recorded fixtures, no AWS): usage 10 x db.r6g.xlarge (80 NU) at 80% (64 NU covered); account A supplies 2 x xlarge expiring in 15d (16 NU); account B's 6 x xlarge long-lived RIs are not in the inventory. True post-expiry coverage is 48 NU, so the gap is 16 NU = 2 x xlarge. Actual result:

count=8 existing=0.0% expiringNU=16 cost=800
over-purchase: bought 8 x xlarge (64 NU), true post-expiry gap is 2 x xlarge (16 NU); deduction 64 NU exceeds expiring 16 NU

That is a 4x over-buy, and it is worse than both the parent (which buys 0) and a plain CoveredNU - expiringNU deduction (which buys 2).

Suggested fix (design call for the plan owner): never deduct more than the expiring NU, and keep the underutilization guard:

fc.CoveredNU = math.Max(0, math.Max(fc.CoveredNU-exp, math.Min(fc.CoveredNU, activeNU[fk]-exp)))

I checked this locally. All 8 PR subtests pass with it, and the reproduction above buys 2. Please add the incomplete-inventory case as a regression test, and update the godoc and CHANGELOG formula to match.

F2 (CI): Lint Code (providers/aws) fails at this SHA, and it is not the known flake.
family_nu.go:425:2: rangeValCopy: each iteration copies 224 bytes (consider pointers or indexing) (gocritic) on for _, c := range commitments. Use indexing (for i := range commitments { c := &commitments[i] ...), as expiringCountsByPool does.

Verified clean

• Additive. sizeRDSFamilies is a verbatim extraction. A golden test copied the parent ApplyFamilyNUSizingRDS body from main and ran 3000 seeded random cases (mixed sizes, engines, Multi-AZ, EC2 rows, unknown sizes, targets 0/50/80/100/101). The new ApplyFamilyNUSizingRDS, WithExpiry(nil commitments) and WithExpiry(window 0) all match the parent exactly, and the report stays zero. Full providers/aws suite passes locally (go1.26.9, GOWORK=off).
• Regression test is meaningful. With the adjustment disabled (parent behaviour), 4 subtests fail: large-RI/xlarge-usage, linked-account, mixed-size, unusable. The outside-window and non-RDS subtests are labelled controls.
• Semantics.
  • Family key comes from rdsFamilyKey, NU from rdsInstanceNUFromType.
  • The expiring filter (EndDate non-zero and not after cutoff) and commitmentIsActive are reused unchanged.
  • The mixed-size test (16 NU active, 8 NU expiring, 12 NU covered, result 8) checks NU, not counts.
  • Count is floored.
  • Linked-account rows are deducted once.
  • Unparsable classes and families missing from coverage are counted as Unusable and never read as "no expiry".
  • payment-pending RIs count as active, so a pending replacement reduces the deduction (conservative).

Non-blocking

• Mutation testing: one targeted mutant (disable the adjustment) was killed. No broader sweep was run.
• CHANGELOG and godoc state the old formula and need updating together with F1.

[cristim]

Addressed F1 and F2 in 707ca12: deduction now capped at expiring NU, max(covered - expiring, min(covered, active - expiring)), with the partial-inventory regression (64 NU covered, 16 expiring supplied, 48 NU missing => count 2, not 8); godoc and CHANGELOG updated; range loop iterates by index. Unit and golangci-lint for providers/aws pass locally.

[cristim]

Independent merge-gate re-review (Opus 5.5, claude-opus-5-5): APPROVED

Reviewed SHA: 707ca12e24174216a67f2a16500a1af6bbe2eb8a (base origin/main 9dae64b, up to date). The delta since 648e1c5 is one commit, 707ca12, which fixes F1 and F2. All evidence below comes from local runs at this SHA (go1.26.9, GOWORK=off) using fixture recs, coverage and commitments. No AWS calls were made.

F1 (over-purchase): fixed.

• The formula is now max(0, max(Covered-exp, min(Covered, active-exp)))) (family_nu.go:449).
• My original repro (64 NU covered, only A's 2 x xlarge (16 NU expiring) supplied) now gives count=2 existing=60.0%. Before the fix it gave 8.
• The new subtest "partial inventory: missing accounts' RIs never remove more than expires" fails when the 648e1c5 formula is put back (uncapped deduction would size 8) and passes at this SHA.

Extra cases (scratch probes, all pass):

case	result
active exceeds covered	count 3, 50% (unchanged)
active is a subset of org coverage (F1)	count 2, 60%
expiring > covered	count 8, 0% (all RIs expire)
zero active in family (only other-family RIs listed)	family dropped at target, Unusable=1
mixed sizes, partial inventory	count 2, 25%

Property check: 5000 random inventories through adjustFamilyCoverageForExpiry (sizes, counts, active and payment-pending states, window-edge end dates). The deduction always stays within [0, expiringNU] for each family. The capped formula cannot remove more coverage than actually expires.

Additive: I re-ran the golden comparison against the parent body copied verbatim from main, 3000 seeds. ApplyFamilyNUSizingRDS, WithExpiry with nil commitments and WithExpiry with window 0 all give identical results and a zero report.

F2 (lint): fixed. The loop now indexes the slice and rdsCommitmentFamilyUnits takes a pointer. CI Lint Code (providers/aws) is green.

Docs: the godoc formula, the CHANGELOG formula and the code agree. The partial-inventory rationale cites cli#2131.

Other checks:

• Full providers/aws suite passes locally.
• Labels match cli#2132.
• All required CI is green at this SHA.

Non-blocking:

• Remaining limitation (documented, owned by cli#2131): when an expiring RI belongs to an account outside the supplied inventory, it is never deducted. This errs toward buying less.
• Mutation testing: two targeted mutants were run (adjustment disabled, uncapped formula) and both were killed. No broader sweep.

CodeRabbit threads (triaged by the gate, replies on each thread): non-size-flexible engine pooling (errs toward under-buying) and the ExpiringNU report wording are non-blocking and tracked in #342. "Require RI commitment type" was dismissed because no RDS-service commitment carries a parseable db class except RIs (see the thread).

CI at 707ca12: all green, including the required checks CI Success and Run pre-commit hooks. The branch is up to date with main 9dae64b.