atenet/dns: return NODATA for non-A queries on actor zone

cmd/atenet/internal/dns/corefile.go

@@ -42,13 +42,30 @@ func buildTemplate() string {
 	// Construct match pattern for <ActorName>.<atespace>.<dnsDomain>. Both the
 	// actor name and the atespace are DNS-1123 labels (same regex).
 	directives = append(directives, fmt.Sprintf("template IN A %s {", resources.ActorDNSSuffix))
-	// Escape the suffix's dots so they match literally; the final \. matches the FQDN's trailing dot.
+	// Escape the suffix's dots so they match literally; the final \\. matches the FQDN's trailing dot.
 	escapedSuffix := strings.ReplaceAll(resources.ActorDNSSuffix, ".", `\.`)
 	directives = append(directives, fmt.Sprintf(`  match "^%s\.%s\.%s\.$"`, resources.ResourceNameRegexPattern, resources.ResourceNameRegexPattern, escapedSuffix))
 	// Note the %s -- this will be filled with the router IP.
 	directives = append(directives, `  answer "{{ .Name }} 60 IN A %s"`)
 	directives = append(directives, "}")
 
+	// Non-A queries for valid actor names must return NODATA (NOERROR with an
+	// empty answer section), not SERVFAIL. CoreDNS's template plugin returns
+	// SERVFAIL when a template's zone matches a query name but no template
+	// block matches the query type (see plugin/template README: "Without
+	// fallthrough, when the template's ZONE matches a query but no regex match
+	// then a SERVFAIL response is returned"). Strict POSIX resolvers query A
+	// and AAAA in parallel and treat SERVFAIL as a hard failure, breaking
+	// intra-cluster resolution for actor images that don't have AAAA records.
+	//
+	// template IN ANY matches every type, and specifying no answer results in
+	// a response with an empty answer section and the default rcode NOERROR —
+	// exactly the NODATA response RFC 8020 expects for a name that exists but
+	// has no records of the requested type.
+	directives = append(directives, fmt.Sprintf("template IN ANY %s {", resources.ActorDNSSuffix))
+	directives = append(directives, fmt.Sprintf(`  match "^%s\.%s\.%s\.$"`, resources.ResourceNameRegexPattern, resources.ResourceNameRegexPattern, escapedSuffix))
+	directives = append(directives, "}")
+
 	// Generate the template.
 	b := strings.Builder{}
 	fmt.Fprintf(&b, "# Generated at %s\n", time.Now())

cmd/atenet/internal/dns/corefile_test.go

@@ -40,6 +40,8 @@ func TestMakeCoreFile(t *testing.T) {
 				"template IN A actors.resources.substrate.ate.dev {",
 				`match "^` + resources.ResourceNameRegexPattern + `\.` + resources.ResourceNameRegexPattern + `\.actors\.resources\.substrate\.ate\.dev\.$"`,
 				`answer "{{ .Name }} 60 IN A 10.240.0.10"`,
+				// Non-A queries must return NODATA, not SERVFAIL.
+				"template IN ANY actors.resources.substrate.ate.dev {",
 			},
 		},
 		{