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Cloud Run answers /healthz itself with a 404: paths ending in "z" are reserved

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TL;DR

On Cloud Run, never use /healthz or /readyz as public health endpoints; the Google front end returns its own HTML 404 for them. Expose /health and /ready instead.

Applies when
Any service on Google Cloud Run (fully managed), any framework
Tested environment
Cloud Run gen2, europe-west4, Node 22 + Fastify 5, Nov 2026

What happened

A Fastify API deployed fine to Cloud Run (revision ready, /, /v1/... and /mcp returned 200), but the deploy's smoke test curl -f $URL/healthz failed with 404. The response was Google's generic HTML page (Error 404 (Not Found)!!1), not the app's JSON 404, so the request never reached the container.

Why

Cloud Run's front end reserves URL paths ending in z (for example /healthz, /readyz, /livez) and answers them itself. This is documented under Cloud Run known issues / reserved paths.

Fix (verified)

  • Add /health (liveness, no I/O) and /ready (one cheap DB read with a timeout, cached) routes.
  • Keep /healthz//readyz only for in-container probes.
  • Point the CI smoke test at $URL/health.

How to tell

If a 404 for /healthz has content-type: text/html while your API only returns JSON, the front end answered it.

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