docs(adr): document the fail-closed dependency contract (ADR-0030) - #487
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docs(adr): document the fail-closed dependency contract (ADR-0030)#487Destynova2 wants to merge 1 commit into
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Competitive analysis of LiteLLM et al. shows silent fail-open (a security dependency becomes unavailable and the request proceeds anyway) is the deadliest gateway defect — LiteLLM's own P0 was budget enforcement failing open on a Redis outage. Audited grob's hot path: budget, DLP, HIT authorization, secret resolution and config load are all already fail-closed (budget reserves in-memory with no external counter store to fail open on; HIT denies on explicit-no, dropped channel AND timeout; invalid config never starts). No behaviour change — this ADR records the classification (authorizing → block, observing → continue) so a future refactor cannot re-introduce a fail-open by accident, and gives reviewers a line to hold. The remaining gap is test coverage of the dependency-unavailable variants, tracked in the fail-closed-granularity issue (#485). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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What
Turns the competitive-analysis finding into a durable contract. The deadliest
gateway defect the analysis surfaces is silent fail-open — LiteLLM's own P0
was budget enforcement failing open on a Redis outage.
I audited grob's hot path for the same class and found it is already
fail-closed on every authorizing dependency:
config.rs:204BudgetExceeded)budget.rs:164/176— spend is in-memory, no external counter store to fail open on?)dispatch/mod.rs:331— deterministic, no "unavailable" stateretry.rs:794-806Notably grob avoids the LiteLLM Redis fail-open structurally (in-memory
synchronous reservation), not by patching around it.
Why an ADR and not a code change
There is no bug to fix — the behaviour is correct. The risk is that a future
refactor silently re-introduces a fail-open (exactly how LiteLLM regressed).
ADR-0030 records the
authorizing → block/observing → continueclassification so reviewers have an explicit line to hold, and flags the one real
gap: test coverage of the dependency-unavailable variants (poisoned mutex,
wedged policy backend), tracked in #485.
Part of the #484/#485/#486 backlog from the competitive analysis.
🤖 Generated with Claude Code