don't fetch cluster domain from kubelet if the user has set it already

Author: razvan

crates/stackable-operator/CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+### Added
+
+- The default Kubernetes cluster domain name is now fetched from the kubelet API unless explicitely configured ([#1068]).
+
 ### Changed
 
 - Update `kube` to `1.1.0` ([#1049]).
@@ -23,6 +27,7 @@ All notable changes to this project will be documented in this file.
 [#1058]: https://github.com/stackabletech/operator-rs/pull/1058
 [#1060]: https://github.com/stackabletech/operator-rs/pull/1060
 [#1064]: https://github.com/stackabletech/operator-rs/pull/1064
+[#1068]: https://github.com/stackabletech/operator-rs/pull/1068
 
 ## [0.93.2] - 2025-05-26
 
@@ -148,7 +153,7 @@ All notable changes to this project will be documented in this file.
 ### Added
 
 - Add Deployments to `ClusterResource`s ([#992]).
-- Add `DeploymentConditionBuilder`  ([#993]).
+- Add `DeploymentConditionBuilder` ([#993]).
 
 ### Changed
 
@@ -369,7 +374,7 @@ All notable changes to this project will be documented in this file.
 ### Fixed
 
 - BREAKING: `KeyValuePairs::insert` (as well as `Labels::`/`Annotations::` via it) now overwrites
-  the old value if the key already exists. Previously, `iter()` would return *both* values in
+  the old value if the key already exists. Previously, `iter()` would return _both_ values in
   lexicographical order (causing further conversions like `Into<BTreeMap>` to prefer the maximum
   value) ([#888]).
 
@@ -634,7 +639,7 @@ All notable changes to this project will be documented in this file.
 
 ### Changed
 
-- Implement `PartialEq` for most *Snafu* Error enums ([#757]).
+- Implement `PartialEq` for most _Snafu_ Error enums ([#757]).
 - Update Rust to 1.77 ([#759])
 
 ### Fixed
@@ -1385,7 +1390,7 @@ This is a rerelease of 0.25.1 which some last-minute incompatible API changes to
 ### Changed
 
 - Objects are now streamed rather than polled when waiting for them to be deleted ([#452]).
-- serde\_yaml 0.8.26 -> 0.9.9 ([#450])
+- serde_yaml 0.8.26 -> 0.9.9 ([#450])
 
 [#450]: https://github.com/stackabletech/operator-rs/pull/450
 [#452]: https://github.com/stackabletech/operator-rs/pull/452

crates/stackable-operator/src/client.rs

@@ -657,10 +657,25 @@ pub async fn initialize_operator(
         .context(InferKubeConfigSnafu)?;
     let default_namespace = kubeconfig.default_namespace.clone();
     let client = kube::Client::try_from(kubeconfig).context(CreateKubeClientSnafu)?;
-    let kubelet_config = kubelet::KubeletConfig::fetch(&client)
-        .await
-        .context(KubeletConfigSnafu)?;
-    let cluster_info = KubernetesClusterInfo::new(&kubelet_config, cluster_info_opts);
+
+    let local_cluster_info_opts = match cluster_info_opts.kubernetes_cluster_domain {
+        None => {
+            trace!("Cluster domain not set, fetching kubelet config to determine cluster domain.");
+
+            let kubelet_config = kubelet::KubeletConfig::fetch(&client)
+                .await
+                .context(KubeletConfigSnafu)?;
+
+            KubernetesClusterInfoOpts {
+                kubernetes_cluster_domain: Some(kubelet_config.cluster_domain),
+            }
+        }
+        _ => KubernetesClusterInfoOpts {
+            kubernetes_cluster_domain: cluster_info_opts.kubernetes_cluster_domain.clone(),
+        },
+    };
+
+    let cluster_info = KubernetesClusterInfo::new(&local_cluster_info_opts);
 
     Ok(Client::new(
         client,

crates/stackable-operator/src/utils/cluster_info.rs

@@ -1,6 +1,9 @@
-use super::kubelet::KubeletConfig;
+use std::str::FromStr;
+
 use crate::commons::networking::DomainName;
 
+const KUBERNETES_CLUSTER_DOMAIN_DEFAULT: &str = "cluster.local";
+
 /// Some information that we know about the Kubernetes cluster.
 #[derive(Debug, Clone)]
 pub struct KubernetesClusterInfo {
@@ -18,19 +21,20 @@ pub struct KubernetesClusterInfoOpts {
 }
 
 impl KubernetesClusterInfo {
-    pub fn new(
-        kubelet_config: &KubeletConfig,
-        cluster_info_opts: &KubernetesClusterInfoOpts,
-    ) -> Self {
+    pub fn new(cluster_info_opts: &KubernetesClusterInfoOpts) -> Self {
         let cluster_domain = match &cluster_info_opts.kubernetes_cluster_domain {
             Some(cluster_domain) => {
                 tracing::info!(%cluster_domain, "Using configured Kubernetes cluster domain");
 
                 cluster_domain.clone()
             }
             None => {
-                let cluster_domain = kubelet_config.cluster_domain.clone();
-                tracing::info!(%cluster_domain, "Using kubelet config cluster domain");
+                // TODO(sbernauer): Do some sort of advanced auto-detection, see https://github.com/stackabletech/issues/issues/436.
+                // There have been attempts of parsing the `/etc/resolv.conf`, but they have been
+                // reverted. Please read on the linked issue for details.
+                let cluster_domain = DomainName::from_str(KUBERNETES_CLUSTER_DOMAIN_DEFAULT)
+                    .expect("KUBERNETES_CLUSTER_DOMAIN_DEFAULT constant must a valid domain");
+                tracing::info!(%cluster_domain, "Defaulting Kubernetes cluster domain as it has not been configured");
 
                 cluster_domain
             }

crates/stackable-operator/src/utils/kubelet.rs

@@ -43,7 +43,6 @@ pub struct KubeletConfig {
 }
 
 impl KubeletConfig {
-
     /// Fetches the kubelet configuration from the "first" node in the Kubernetes cluster.
     pub async fn fetch(client: &Client) -> Result<Self, Error> {
         let api: Api<Node> = Api::all(client.clone());