IPv6-only domains do not resolve, cannot be scanned

[Barnoux]

What information was incorrect, unhelpful, or incomplete?

When attempting to scan https://vaultwarden.one4all.icu:35689, I receive an HTTP 422 error with the following response:

{
    "error": "invalid-hostname-lookup",
    "message": "www.vaultwarden.one4all.icu cannot be resolved"
}

How my website is setup ?

• The hostname I provided was: vaultwarden.one4all.icu:35689,
• The error message references: www.vaultwarden.one4all.icu,
• The site vaultwarden.one4all.icu:35689 is working fine with DNS resolution and HTTPS accessibility,
• The site uses IPv6.

What input did i provide ?

• vaultwarden.one4all.icu:35689
• https://vaultwarden.one4all.icu:35689

Actual Behavior

• The system appears to be prepending "www." to the hostname,
• Since www.vaultwarden.one4all.icu doesn't have a record DNS, the scan fails.

Impact

• I cannot scan my hostname,
• Error messages are misleading and don't reflect what input from the user is expected.

What did you expect to see?

The system should be able to scan the hostname vaultwarden.one4all.icu on port 35689 with HTTPS protocol.

[caugner]

Can reprodcue:

$ curl https://observatory-api.mdn.allizom.net/api/v2/analyze\?host\=vaultwarden.one4all.icu:35689   
{"error":"invalid-hostname-lookup","message":"www.vaultwarden.one4all.icu cannot be resolved"}

It works locally:

$ npx @mdn/mdn-http-observatory vaultwarden.one4all.icu:35689
{
  "scan": {
    "algorithmVersion": 4,
    "grade": "B+",
    "error": null,
    "score": 80,
    "statusCode": 200,
    "testsFailed": 1,
    "testsPassed": 9,
    "testsQuantity": 10,
    // ...
}

This suggests we have an IPv6 issue in our setup.

[globau]

Thank you for the report; from some quick checks of other IPv6-only domains (including ones with a www. subdomain) it appears that IPv6 is not functional currently. We'll investigate and get this addressed, if possible.

[caugner]

I filed an internal ticket (SREIN-950) to verify the outgoing IPv6 connectivity of the Observatory API.

[caugner]

The infra team has confirmed that this is a known limitation, and they have plans to resolve this with an upcoming migration.

For now, I will mark this issue as blocked.

[globau]

The infra team are expecting this to be viable in Q3 2026.