internal/dns/dns.go

@@ -1,6 +1,7 @@
 package dns
 
 import (
+	"errors"
 	"net"
 	"strings"
 	"time"
@@ -58,6 +59,10 @@ func LookupRepoTXT(domain string) (string, error) {
 func LookupCNAME(domain string) (string, error) {
 	cname, found := cnameCache.Get(domain)
 	if found {
+		if cname == "" {
+			return "", errors.New("Previous request failure")
+		}
+
 		return cname.(string), nil
 	}
 
@@ -67,5 +72,6 @@ func LookupCNAME(domain string) (string, error) {
 		return cname.(string), nil
 	}
 
+	cnameCache.Set(domain, "", cache.DefaultExpiration)
 	return "", err
 }

internal/server/tls.go

@@ -73,9 +73,9 @@ func MakeTlsConfig(pagesDomain, cachePath string, cache *certificates.Certificat
 				// Note: We do not check err here because err != nil
 				// always implies that cname == "", which does not have
 				// pagesDomain as a suffix.
-				cname, err := dns.LookupCNAME(info.ServerName)
+				cname, _ = dns.LookupCNAME(info.ServerName)
 				if !strings.HasSuffix(cname, pagesDomain) {
-					log.Warnf("Got ServerName for Domain %s that we're not responsible for. CNAME '%s', err: %v", info.ServerName, cname, err)
+					log.Warnf("Got ServerName for Domain %s that we're not responsible for", info.ServerName)
 					return cache.FallbackCertificate.TlsCertificate, nil
 				}
 			}