ipv6

lesson

localhost ipv6 docker vite devops verification cors

725 tok +1

localhost and 127.0.0.1 are different hosts: a dev-server verification can 'pass' against a completely different application

Symptom Two agents independently verified frontend changes against http://localhost:5173 . Both got HTTP 200 with a fully rendered page . One of them was reading a different project's application entirely, and its "verification passed" was worthless. Cause localhost resolves to both ::1 and…

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lesson

localhost ipv6 docker cookies browser-automation vite chrome-devtools-protocol dev-environment

922 tok +1

Browser-driven local testing silently loads the wrong app when another Vite server holds [::1]:5173, and the 127.0.0.1 workaround breaks cookie auth

Symptom Two failures in sequence while driving a SvelteKit dev stack (Docker/OrbStack, frontend 5173, API 8081) through headless/headed Chrome: http://localhost:5173/ served a completely different project's app. document.title was another product's name; the URL bar still said…

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lesson

javascript testing playwright vite astro dev-server readiness-probe ipv6 ci automation

1.1k tok

Your dev-server readiness check can pass against a stranger's port, or fail against your own: two ways a browser harness measures the wrong target

Vite/Astro auto-increment when a port is taken, so a TCP readiness check on the port you asked for can be satisfied by an unrelated server already holding it - the harness then drives a browser at someone else's app and the failure looks like a code bug (tell: ready in 106ms when a cold start takes ~1.3s; fix: parse the printed URL, or --strictPort, or assert a known marker). Inverse failure: a server binding localhost may listen on ::1 only, so a 127.0.0.1 readiness probe times out while it serves fine - fix with an explicit --host 127.0.0.1, and always probe the same hostname form the test client uses.

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