Align revalidate seconds with cache behaviour#17
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* It is now explicit that it only controls the metrics cache
* Next, we'll rename it so that future contributors do not run into
the same confusion
* This drops the Next.js "revalidate" terminology and makes it clearer
that this is its own thing unrelated to Next.js revalidation
* Extract the calculation into a function to avoid drift
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kilemensi
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Mostly looks good to me ... Only thing I can think of is a metricsCacheSeconds < revalidate is pointless because pages will still show old data until revalidate expires.
METRICS_CACHE_SECONDS was documented as *the* bound on data freshness for all routes. That is wrong for the overview page: `/` is cached by a fixed `revalidate = 60` ISR literal and only regenerates on that interval, so its effective freshness is max(revalidate, METRICS_CACHE_SECONDS). Lowering the metrics cache below 60s buys no extra freshness on `/` — it only speeds up the on-demand detail route.
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@kilemensi I've captured that more clearly in the docs. |
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What & why
REVALIDATE_SECONDSwas documented as controlling both the server-side Prometheus/data cache and the ISR page-revalidation window, but the two layers never actually agreed:/) hardcodedexport const revalidate = 60, ignoring the configured value./site/[id]) also exportedrevalidate = 60, but readssearchParams, so it's server-rendered on demand — the export was dead.unstable_cache+ Prometheusfetch) honored the configured value.Next.js 16 requires a route's
revalidateto be a statically-analyzable literal, so an env var cannot drive route ISR — meaning the "both layers" contract was impossible to satisfy. On top of that, the overview'supdatedtimestamp was stamped at render time, so it could advance while showing older cached metrics.This PR gives the setting one accurate meaning and makes the timestamp honest:
REVALIDATE_SECONDS→METRICS_CACHE_SECONDS(andconfig.revalidate→config.metricsCacheSeconds). The old name echoed Next's route-segmentrevalidate— exactly the layer it does not control. No back-compat fallback (codebase is still young; a clean break was chosen deliberately).METRICS_CACHE_SECONDSnow means only the data-cache window — how often Grafana is queried. Route rendering is documented as separate:/keeps a fixedrevalidate = 60literal;/site/[id]drops its dead export and is dynamic.updatedvalue now reflects real data-fetch time.getOverview()returns a newOverviewData({ checks, fetchedAt }), withfetchedAtcaptured inside the cached function so it only advances on a cache miss.README.md,docs/configuration.md,docs/architecture.md,.env.example,AGENTS.md) updated to match.Closes #11
Type of change
Checklist
[AGENTS.md](https://claude.ai/AGENTS.md)and[CONTRIBUTING.md](https://claude.ai/CONTRIBUTING.md)pnpm checkpasses — ranpnpm lint:ci(the check-only variant) which passes; did not run the autofixingpnpm checkpnpm testpasses — 103 passingpnpm test:typespassespnpm buildsucceeds — please run in CI; a fullpnpm buildwas verified against an earlier state of the branch but not re-run after the final rename (types + tests + lint pass on the final state)lib/synthetics.test.tsandlib/prometheus.test.tsupdated for the new return shape and config field; assertsfetchedAtis presentdocs/) if behaviour or configuration changedNEXT_PUBLIC_prefixNotes for reviewers
REVALIDATE_SECONDSis removed, not aliased. Any deployment still setting it will silently fall back to the60s default until it's renamed toMETRICS_CACHE_SECONDS. Intentional given the project's age — call out if you'd prefer a deprecation window.METRICS_CACHE_SECONDS=300, the build still reports/atRevalidate 1m. That's now correct and documented — the route re-renders at most every 60s but reads cached data, andupdatedshows the true fetch time (up to 300s old) rather than lying.fetchedAt; the detail page has no "updated" label, sogetSiteHistoryintentionally doesn't carry it.updatedtimestamp — no screenshots needed.Acceptance criteria
REVALIDATE_SECONDShas one accurate, consistently documented meaning.updatedvalue represents metric freshness rather than only render time.README.md,.env.example,docs/configuration.md, anddocs/architecture.mdmatch production behavior.