Outbound HTTPS timeouts to MIMIT CSV endpoints from Node.js functions in iad1 and fra1

Hi,

I’m investigating outbound HTTPS timeouts from Vercel Node.js Functions when downloading two public CSV datasets from the Italian Ministry of Enterprises (MIMIT):

https://www.mimit.gov.it/images/exportCSV/prezzo_alle_8.csv

https://www.mimit.gov.it/images/exportCSV/anagrafica_impianti_attivi.csv

Environment

Vercel Hobby plan, Preview deployments
Next.js 16.3.4
Node.js 24.x runtime, explicitly configured as nodejs
Function regions verified separately from the build region

Controlled tests

Native Node fetch, wrapped by Next.js, in iad1: both downloads failed with UND_ERR_CONNECT_TIMEOUT after approximately 10.45 seconds, before receiving HTTP response headers.
The same application code in fra1: both downloads failed with the same error after approximately 10.44 seconds.
A temporary transport using node:https.request() with per-request family: 4, also in fra1: both downloads failed with ETIMEDOUT after approximately 15.46 seconds, before receiving response headers.

The application has a 30-second overall download timeout. These failures occurred before that deadline. No automatic retries were used.

The IPv4 experiment retained the original hostname and default TLS certificate verification. No fixed IPs, custom certificates or application-level proxies were used. Neither CSV download completed during that test.

A previous download of the prices CSV from my Mac succeeded with HTTP 200 and valid CSV content. However, that local test was not simultaneous with the Vercel tests.

Example server diagnostic

{
  "event": "mimit_dataset_failure",
  "dataset": "prezzo_alle_8.csv",
  "phase": "fetch_headers",
  "category": "network",
  "code": "UND_ERR_CONNECT_TIMEOUT",
  "durationMs": 10464
}

The temporary IPv4 transport has since been reverted locally. We have not identified whether the cause is destination-side filtering, DNS/TCP/TLS connectivity, routing, or another issue between Vercel and the upstream host.

Could you suggest the next targeted diagnostic step? Are there any known outbound connectivity issues or restrictions relevant to this destination?

I have deployment IDs and exact UTC timestamps available if a Vercel staff member needs them through an appropriate support channel.

Thank you, Erasmo

Hi,