feat: improve DNS lookup performance

Author: dervoeti

crates/stackable-operator/src/commons/networking.rs

@@ -17,8 +17,11 @@ impl FromStr for DomainName {
     type Err = validation::Errors;
 
     fn from_str(value: &str) -> Result<Self, Self::Err> {
+        // Remove optional trailing dot before validation, logic taken from https://github.com/kubernetes/kubernetes/blob/30de989fb57fb5921a7ae3e3203cf7ecac9cf3f0/staging/src/k8s.io/apimachinery/pkg/util/validation/validation.go#L100
+        let value = value.strip_suffix('.').unwrap_or(value);
         validation::is_rfc_1123_subdomain(value)?;
-        Ok(DomainName(value.to_owned()))
+        // Append trailing dot to make the domain name a FQDN to improve DNS lookup performance, see https://github.com/stackabletech/issues/issues/656
+        Ok(DomainName(format!("{}.", value)))
     }
 }