fix: ensure ipv4 is checked, not sometimes ipv6

See coop-cloud/organising#490

pkg/dns/dns.go

@@ -7,11 +7,16 @@ import (
 
 // EnsureIPv4 ensures that an ipv4 address is set for a domain name
 func EnsureIPv4(domainName string) (string, error) {
-	ipv4, err := net.ResolveIPAddr("ip", domainName)
+	ipv4, err := net.ResolveIPAddr("ip4", domainName)
 	if err != nil {
 		return "", err
 	}
 
+	// NOTE(d1): e.g. when there is only an ipv6 record available
+	if ipv4 == nil {
+		return "", fmt.Errorf("unable to resolve ipv4 address for %s", domainName)
+	}
+
 	return ipv4.String(), nil
 }