review: derive atenet's system namespace from POD_NAMESPACE

Same rationale as the prior atelet-namespace change: atenet, atenet-router,
and substrate's CoreDNS live in a single namespace in every supported
deployment topology, so a separate --system-namespace flag was dead
weight. Resolve from the POD_NAMESPACE env var (Kubernetes' downward
API) with installdefaults.SystemNamespace as the fallback for non-k8s
runs.

--router-service-name and --dns-service-name stay as flags because a
subchart deployment renames those Services with a release prefix, and
the binary can't derive that from pod metadata.

Author: jjamroga

charts/substrate/templates/atenet-dns.yaml

@@ -150,11 +150,16 @@ spec:
         - "--log-level=debug"
         - "--interval=10s"
         - "--corefile-path=/etc/coredns/Corefile"
-        # Pass the chart-resolved names/namespace so the controller looks up
-        # the correct Services when substrate is installed as a subchart.
-        - "--system-namespace={{ .Release.Namespace }}"
+        # Pass the chart-resolved Service names so the controller looks up the
+        # correct objects when substrate is installed as a subchart. The
+        # system namespace is read from POD_NAMESPACE below.
         - "--router-service-name={{ include "substrate.fullname" (list "atenet-router" .) }}"
         - "--dns-service-name={{ include "substrate.fullname" (list "dns" .) }}"
+        env:
+        - name: POD_NAMESPACE
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.namespace
         volumeMounts:
         - name: dns-config-volume
           mountPath: /etc/coredns

cmd/atenet/internal/dns.go

@@ -38,7 +38,6 @@ type DnsConfig struct {
 	Kubeconfig        string
 	ReconcileInterval time.Duration
 	CorefilePath      string
-	SystemNamespace   string
 	RouterServiceName string
 	DNSServiceName    string
 }
@@ -90,12 +89,22 @@ func NewDnsCmd() *cobra.Command {
 				return fmt.Errorf("failed to initialize cluster client: %w", err)
 			}
 
+			// atenet shares the system namespace with atenet-router and
+			// substrate's CoreDNS in every supported deployment topology.
+			// POD_NAMESPACE comes from Kubernetes' downward API; the install
+			// fallback keeps non-k8s invocations (tests, local dev) working.
+			systemNamespace := os.Getenv("POD_NAMESPACE")
+			if systemNamespace == "" {
+				systemNamespace = installdefaults.SystemNamespace
+			}
+			slog.InfoContext(ctx, "Resolved system namespace", slog.String("system-namespace", systemNamespace))
+
 			dnsController := &dns.Controller{
 				Client:            k8sClient,
 				Interval:          cfg.ReconcileInterval,
 				CorefilePath:      cfg.CorefilePath,
 				Reloader:          dns.NewConfigReloader(),
-				SystemNamespace:   cfg.SystemNamespace,
+				SystemNamespace:   systemNamespace,
 				RouterServiceName: cfg.RouterServiceName,
 				DNSServiceName:    cfg.DNSServiceName,
 			}
@@ -109,7 +118,6 @@ func NewDnsCmd() *cobra.Command {
 	cmd.Flags().StringVar(&cfg.Kubeconfig, "kubeconfig", "", "Absolute path to the kubeconfig configuration file")
 	cmd.Flags().DurationVar(&cfg.ReconcileInterval, "interval", 10*time.Second, "Interval for reconciling DNS configurations")
 	cmd.Flags().StringVar(&cfg.CorefilePath, "corefile-path", "/etc/coredns/Corefile", "Path to the local Corefile configuration on shared volume")
-	cmd.Flags().StringVar(&cfg.SystemNamespace, "system-namespace", installdefaults.SystemNamespace, "Namespace where atenet-router and substrate's CoreDNS Service live. Override when the deployment uses a different namespace.")
 	cmd.Flags().StringVar(&cfg.RouterServiceName, "router-service-name", installdefaults.RouterServiceName, "Service name of the atenet-router. Override when the deployment renames the Service.")
 	cmd.Flags().StringVar(&cfg.DNSServiceName, "dns-service-name", installdefaults.DNSServiceName, "Service name of substrate's CoreDNS. Override when the deployment renames the Service.")
 

manifests/ate-install/atenet-dns.yaml

@@ -170,11 +170,16 @@ spec:
         - "--log-level=debug"
         - "--interval=10s"
         - "--corefile-path=/etc/coredns/Corefile"
-        # Pass the chart-resolved names/namespace so the controller looks up
-        # the correct Services when substrate is installed as a subchart.
-        - "--system-namespace=ate-system"
+        # Pass the chart-resolved Service names so the controller looks up the
+        # correct objects when substrate is installed as a subchart. The
+        # system namespace is read from POD_NAMESPACE below.
         - "--router-service-name=atenet-router"
         - "--dns-service-name=dns"
+        env:
+        - name: POD_NAMESPACE
+          valueFrom:
+            fieldRef:
+              fieldPath: metadata.namespace
         volumeMounts:
         - name: dns-config-volume
           mountPath: /etc/coredns