perf(health): CDN-cache compact health, 5-min client cadence, idle-deferred first hydration (#4907) by koala73 · Pull Request #4908 · koala73/worldmonitor

koala73 · 2026-07-05T17:41:15Z

Fixes #4907. Follow-up to #4902 / PR #4905.

Problem

Every /api/health invocation runs a ~196-key Upstash pipeline (STRLEN+GET per check) and every response was no-store end to end — so origin probe cost scaled linearly with open dashboard tabs (60s cadence, runImmediately: true, all variants), and the first fetch sat in the startup critical window (relevant to field-LCP issue #4890). The underlying seed cadences are 6–24h; per-minute per-tab probing buys nothing.

Changes

CDN-cache the compact form (api/health.js): compact 200s get Cache-Control: public, max-age=0, must-revalidate + CDN-Cache-Control: public, s-maxage=60, and drop the hardcoded CF-Cache-Status: BYPASS marker. All tabs/users collapse onto ~one origin probe per cache window per edge region. Key-gated detailed responses, 401s, and the REDIS_DOWN 503 keep no-store — caching the detailed form could leak an operator view across a shared cache, caching a 401 pins an auth failure, caching a 503 masks recovery from HTTP monitors.
Client cadence 60s → 5min (src/config/variants/base.ts): safe margin under the 15-min FRESH_THRESHOLD, so synthesized-OK sources (age-less since PR fix(health-freshness): read the keyless compact health endpoint — stop the anon 401-per-minute flood (#4902) #4905) cannot decay to stale between polls. Staleness-onset detection goes ≤1min → ≤6min (poll + cache window) — noise at 6–24h seed cadences. The 15-min 401/403 suppression window from fix(health-freshness): read the keyless compact health endpoint — stop the anon 401-per-minute flood (#4902) #4905 still spans ~3 ticks.
Idle-defer the first hydration (src/App.ts): the health-freshness registration (including its immediate first run) now goes through scheduleAfterFirstPaint, keeping the fetch out of the LCP window. Freshness badges are below-the-fold decoration; the scheduler's pauseWhenHidden behavior is unchanged.

Verification

New tests/health-compact-cdn-cache.test.mjs (handler-level, mocked Upstash pipeline): compact-200 cache headers; no-store pinned on detailed-200 / keyless-401 / REDIS_DOWN-503. 4/4 pass.
Scheduler-shape pin in tests/data-freshness-health.test.mts updated to require the post-paint defer; 13/13 pass. Existing health server suites (11/11) green.
npm run typecheck, docs-stats --check, lint:api-contract clean; tiered pre-push gate green.
Post-deploy: will re-probe prod ?compact=1 headers (a Cloudflare cache rule is already active on this path — cf-cache-status: EXPIRED observed — so live behavior needs confirming; origin intent is now correct for Vercel edge cache + CF respect-origin either way).

https://claude.ai/code/session_01YKrVoDp8TfEKLYXo83kPFV

…, 5-min cadence, idle-deferred first hydration (#4907) Every /api/health call runs a ~196-key Upstash pipeline and responses were no-store end to end, so origin probe cost scaled linearly with open tabs (60s x per-tab x all variants) and the first fetch competed with the LCP window (#4890). - api/health.js: compact 200s (the public keyless form) get Cache-Control: public, max-age=0, must-revalidate + CDN-Cache-Control: public, s-maxage=60 — all tabs collapse onto ~one origin probe per cache window per edge region. Key-gated detailed responses, 401s, and the REDIS_DOWN 503 keep no-store (caching a 401 pins an auth failure; caching a 503 masks recovery). - REFRESH_INTERVALS.healthFreshness 60s -> 5min: seed cadences are 6-24h and badge decay is client-computed; 5min stays safely under the 15min FRESH_THRESHOLD so synthesized-OK sources (age-less since #4905) cannot decay to stale between polls. - App.ts: health-freshness registration (and its immediate first run) deferred via scheduleAfterFirstPaint — freshness badges are below-the-fold decoration and must not compete with LCP requests. New tests: compact-200 cache headers + no-store pins for detailed/401/503 (handler-level, mocked Upstash pipeline); scheduler-shape pin updated to require the post-paint defer. Fixes #4907 Claude-Session: https://claude.ai/code/session_01YKrVoDp8TfEKLYXo83kPFV

vercel · 2026-07-05T17:41:21Z

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
worldmonitor	Ready	Preview, Comment	Jul 5, 2026 5:44pm

greptile-apps · 2026-07-05T17:45:02Z

Greptile Summary

This PR reduces origin load and LCP-window cost for the /api/health polling path by three coordinated changes: CDN-caching the compact public form (60 s s-maxage), slowing the client poll from 60 s to 5 min, and deferring the first hydration fetch to post-paint idle time.

api/health.js: Compact 200 responses now carry Cache-Control: public, max-age=0, must-revalidate + CDN-Cache-Control: public, s-maxage=60; the hardcoded CF-Cache-Status: BYPASS marker is removed. Key-gated detailed responses, 401s, and REDIS_DOWN 503s all hit early-return paths before this block and keep no-store.
src/config/variants/base.ts: healthFreshness interval raised from 60 s to 5 min — a safe margin under the 15-min FRESH_THRESHOLD.
src/App.ts: Health-freshness scheduler registration wrapped in scheduleAfterFirstPaint, keeping the first Upstash pipeline out of the LCP window.

Confidence Score: 4/5

Safe to merge; all error paths (503, 401, key-gated 200) correctly bypass the new caching block and keep no-store.

The cache logic is correct and well-tested. The one notable gap is that the cacheable compact response is built by spreading getCorsHeaders() output, which injects Vary: Origin and a request-scoped Access-Control-Allow-Origin into the cached headers. CDNs that respect Vary will fragment the cache per distinct client origin rather than serving a single shared entry, partially working against the stated goal. getPublicCorsHeaders() exists in _cors.js for exactly this scenario. In production, with essentially one primary origin, the impact is small, but worth addressing before the CDN behavior is treated as fully resolved.

The CORS header selection in api/health.js around the compact caching block deserves a second look — using getPublicCorsHeaders() there instead of the per-request CORS headers would eliminate Vary: Origin cache fragmentation.

Important Files Changed

Filename	Overview
api/health.js	Adds CDN-cacheable headers for compact 200 responses; correctness is sound (503/401 early-return before the cache block), but the cacheable block spreads getCorsHeaders() which injects Vary: Origin, partially undermining the single-cache-entry-per-region goal.
src/App.ts	Wraps the health-freshness scheduler registration in scheduleAfterFirstPaint, deferring the first hydration out of the LCP window; runImmediately: true is preserved so the fetch fires right after paint.
src/config/variants/base.ts	Increases healthFreshness poll cadence from 60s to 5min; well within the 15-min FRESH_THRESHOLD boundary documented in the inline comment.
tests/health-compact-cdn-cache.test.mjs	New 4-case handler-level test: compact-200 cacheable, detailed-200 no-store, keyless-401 no-store, compact-503 no-store. Covers all stated caching invariants cleanly.
tests/data-freshness-health.test.mts	Updates the structural regex pin to require the new scheduleAfterFirstPaint wrapper; assertion message updated to reflect the post-paint intent.

Sequence Diagram

%%{init: {'theme': 'neutral'}}%%
sequenceDiagram
    participant Tab as Dashboard Tab
    participant Edge as CDN/Edge Cache
    participant Origin as Vercel Origin
    participant Redis as Upstash Redis

    Note over Tab: After first paint (idle-deferred)
    Tab->>Edge: "GET /api/health?compact=1"
    alt Cache MISS (or expired after 60s)
        Edge->>Origin: Forward request
        Origin->>Redis: Pipeline (196 keys)
        Redis-->>Origin: Results
        Origin-->>Edge: "200 + CDN-Cache-Control: s-maxage=60"
        Edge-->>Tab: 200 (cache MISS)
        Note over Edge: Cached for 60s
    else Cache HIT
        Edge-->>Tab: 200 (cache HIT, no Redis probe)
    end

    Note over Tab: Every 5 min (was every 60s)
    Tab->>Edge: "GET /api/health?compact=1"
    Edge-->>Tab: 200 (likely cache HIT)

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
sequenceDiagram
    participant Tab as Dashboard Tab
    participant Edge as CDN/Edge Cache
    participant Origin as Vercel Origin
    participant Redis as Upstash Redis

    Note over Tab: After first paint (idle-deferred)
    Tab->>Edge: "GET /api/health?compact=1"
    alt Cache MISS (or expired after 60s)
        Edge->>Origin: Forward request
        Origin->>Redis: Pipeline (196 keys)
        Redis-->>Origin: Results
        Origin-->>Edge: "200 + CDN-Cache-Control: s-maxage=60"
        Edge-->>Tab: 200 (cache MISS)
        Note over Edge: Cached for 60s
    else Cache HIT
        Edge-->>Tab: 200 (cache HIT, no Redis probe)
    end

    Note over Tab: Every 5 min (was every 60s)
    Tab->>Edge: "GET /api/health?compact=1"
    Edge-->>Tab: 200 (likely cache HIT)

_{Reviews (1): Last reviewed commit: "perf(health): collapse health polling co..." | Re-trigger Greptile}

greptile-apps · 2026-07-05T17:45:06Z

+  let responseHeaders = headers;
+  if (compact) {
+    const { 'CF-Cache-Status': _bypassMarker, ...cacheable } = headers;
+    responseHeaders = {
+      ...cacheable,
+      'Cache-Control': 'public, max-age=0, must-revalidate',
+      'CDN-Cache-Control': 'public, s-maxage=60',
+    };
+  }


Vary: Origin fragments the CDN cache per client origin

The cacheable spread includes getCorsHeaders(req) output, which sets Access-Control-Allow-Origin: <request-origin> and Vary: Origin. Any CDN that respects Vary (including Cloudflare and Vercel edge) will create a separate cache entry per distinct Origin value — so preview deployments, tauri://localhost, and the production origin each get their own entry. The stated goal of "one origin probe per cache window per edge region" is partially defeated.

_cors.js already exports getPublicCorsHeaders() designed exactly for public cacheable responses: it sets ACAO: *, omits Vary: Origin, and its docstring explains the same fragmentation concern. Since isDisallowedOrigin() already blocks unauthorized origins earlier in the handler and the compact form is keyless (no credentials needed), the cacheable block can safely use getPublicCorsHeaders() to produce a single cache entry per path per region.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

… would oscillate synthesized-OK sources to stale (#4910) (#4912) Cloudflare's zone Browser-Cache-TTL override rewrites the compact health endpoint's max-age=0 to 30min (observed live post-#4908). Synthesized-OK sources compute freshness from checkedAt against the 15-min FRESH_THRESHOLD, so a browser-cached body 15-30min old flips every healthy badge to stale, then back on the next cache window — oscillating ~30min waves. fetch cache: 'no-cache' forces revalidation on every poll; Cloudflare answers from its 60s edge cache, so the #4907 origin collapse is intact and checkedAt stays well under threshold. Fixes #4910 Claude-Session: https://claude.ai/code/session_01YKrVoDp8TfEKLYXo83kPFV

koala73 enabled auto-merge (squash) July 5, 2026 17:41

vercel Bot deployed to Preview July 5, 2026 17:44 View deployment

koala73 merged commit c6db71f into main Jul 5, 2026
26 checks passed

greptile-apps Bot reviewed Jul 5, 2026

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

perf(health): CDN-cache compact health, 5-min client cadence, idle-deferred first hydration (#4907)#4908

perf(health): CDN-cache compact health, 5-min client cadence, idle-deferred first hydration (#4907)#4908
koala73 merged 1 commit into
mainfrom
perf/health-polling-cost

koala73 commented Jul 5, 2026

Uh oh!

vercel Bot commented Jul 5, 2026 •

edited

Loading

Uh oh!

Uh oh!

greptile-apps Bot commented Jul 5, 2026

Uh oh!

greptile-apps Bot Jul 5, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

Conversation

koala73 commented Jul 5, 2026

Problem

Changes

Verification

Uh oh!

vercel Bot commented Jul 5, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

greptile-apps Bot commented Jul 5, 2026

Greptile Summary

Confidence Score: 4/5

Important Files Changed

Sequence Diagram

Uh oh!

greptile-apps Bot Jul 5, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

vercel Bot commented Jul 5, 2026 •

edited

Loading