81 lines
4.4 KiB
Markdown
81 lines
4.4 KiB
Markdown
# ADR-MONGO-ADV-001 — Advanced capability promotion
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- **Status:** Accepted
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- **Date:** 2026-08-13
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- **Design source:** design §2 (D-15), §3.2–§3.3; Advanced expansion plan Task 15
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## Context
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Sharding, time series, CSFLE, Queryable Encryption, search, vector search and multi-tenancy each work
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in a demo within an afternoon. What they do not do is behave the same way in production, and the
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differences are not discovered by functional tests:
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- Sharding changes which queries are efficient. A query that misses the shard key becomes
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scatter-gather, which passes every test on a one-shard cluster.
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- Encryption's failure modes are KMS failure modes — wrong key, revoked permission, mid-rotation —
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none of which occur against a local key provider.
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- Search and vector search can be functionally correct and useless: the index returns results, and
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the results are not relevant. Recall is not visible in a pass/fail assertion.
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- Database-per-tenant works until the tenant count crosses what the connection and file-handle
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budget supports, which is an operational property, not a code property.
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The failure mode this ADR prevents is a capability marked "done" on the strength of a green test that
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never touched the environment where it will run.
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## Decision
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Every Advanced and Experimental capability is an **opt-in module behind its own flag**, and promotion
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requires evidence, not confidence.
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### Enablement
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`MongoAdvancedCapabilityFlags` gates construction of every Advanced entry point. A disabled capability
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does not produce a runtime warning — the type refuses to be constructed, naming the property that
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enables it (`MongoAdvancedCapabilityFlags.propertyFor(capability)`). Being on the classpath is not
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being enabled, and `stableNeverDependsOnAdvanced` (ArchUnit) keeps the Stable surface free of them.
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### Promotion evidence
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`MongoAdvancedPromotionGate.verify(evidence)` requires every category:
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| Category | Means |
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|---|---|
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| `stable-platform` | The Stable release gate passed on the same revision. |
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| `actual-topology` | The capability ran on the real topology — a real sharded cluster, the real KMS, the actual target deployment. Atlas Local is a pull-request convenience and explicitly not release evidence (`MongoAtlasCapabilityContractSuite.Environment.ATLAS_LOCAL`). |
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| `security` | Privileges reviewed; the capability's admin role is separate from the application role. |
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| `migration` | A documented path in and, where the capability is irreversible, an explicit statement that there is no path back. |
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| `failure` | Negative cases fail closed: wrong key, missing permission, rotation, non-ready index, unrouted query. |
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| `runbook` | A runbook exists for the capability's characteristic incident. |
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### Additional per-capability requirements
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- **Search / vector search:** relevance and performance evidence, not functional success alone.
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`MongoVectorSearchBenchmarkGate` requires recall alongside latency and index size; a gate that
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measures only latency certifies a fast wrong answer.
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- **Database-per-tenant and reshard orchestration remain Experimental** until operational scale
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evidence exists. Both are correct in the small and unbounded in the large.
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- **Reshard requires an explicit `ReshardApproval`** — a named approver and a stated window. It
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rewrites the collection.
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### Promotion does not change the dependency boundary
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A capability promoted to Stable **remains an opt-in module** unless a later starter ADR changes the
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dependency boundary. Promotion is a statement about evidence, not an invitation to add a transitive
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dependency to every service.
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## Consequences
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**Positive.** No capability reaches production on the strength of a container-only test. The evidence
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list is the same for every capability, so promotion is reviewable rather than negotiated.
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**Negative.** Promotion requires access to real infrastructure — a sharded cluster, a real KMS, the
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target deployment. That is the cost of the guarantee: the alternative is finding out in production,
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where encryption and sharding are both expensive to reverse.
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## Verification
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`scripts/verify-mongodb-advanced.sh` enforced this ADR until it was removed on 2026-08-15. The
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promotion evidence categories this ADR requires are therefore no longer checked by any automated
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gate; they are a review obligation until one is rebuilt. See `docs/mongodb/repository-adaptation.md`
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§5 for the Gradle lanes the script wrapped.
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