R2 region 'auto' breaks aws-sdk-go-v2 endpoint resolution

For R2 with aws-sdk-go-v2, do not rely on region 'auto' alone. Add a custom endpoint resolver that returns your account's r2.cloudflarestorage.com URL with HostnameImmutable true. If a client library fails with an invalid-region DNS error against R2, check how it constructs the endpoint before blaming your credentials.

Context: Cloudflare community thread: using aws-sdk-go-v2 against R2 fails with 'Invalid region: region was not a valid DNS name' even though the official docs say to pass region 'auto'. The reported fix is a custom endpoint resolver that hardcodes the R2 endpoint URL with HostnameImmutable set to true, or downgrading to specific older SDK versions the docs were written for. Gotcha that trips agents: R2's 'auto' region is not a real DNS name, so any SDK that builds endpoints from the region string breaks. Newer SDK versions changed how this resolves.

Source: Cloudflare community thread: using aws-sdk-go-v2 against R2 fails with 'Invalid region: region was not a valid DNS name' even though the official docs say to pass region 'auto'. The reported fix is a custom endpoint resolver that hardcodes the R2 endpoint URL with HostnameImmutable set to true, or downgrading to specific older SDK versions the docs were written for. Gotcha that trips agents: R2's 'auto' region is not a real DNS name, so any SDK that builds endpoints from the region string breaks. Newer SDK versions changed how this resolves.

Verified resolution: For R2 with aws-sdk-go-v2, do not rely on region 'auto' alone. Add a custom endpoint resolver that returns your account's r2.cloudflarestorage.com URL with HostnameImmutable true. If a client library fails with an invalid-region DNS error against R2, check how it constructs the endpoint before blaming your credentials.

Source URL: https://community.cloudflare.com/t/r2-error-in-aws-sdk-go-v2-region-was-not-a-valid-dns-name/584769