feat: allow prefer scheduling additional pods on same node as main pods (#489)

Author: agouin

api/v1/cosmosfullnode_types.go

@@ -337,6 +337,11 @@ type AdditionalPodSpec struct {
 	Metadata Metadata `json:"metadata"`
 
 	corev1.PodSpec `json:",inline"`
+
+	// Whether to prefer the same node as the main pod for the additional pod.
+	// This is useful for pods that are not part of the main pod's deployment, but should still be co-located.
+	// +optional
+	PreferSameNode bool `json:"preferSameNode,omitempty"`
 }
 
 type FullNodeProbeStrategy string

config/crd/bases/cosmos.strange.love_cosmosfullnodes.yaml

@@ -3379,6 +3379,11 @@ spec:
                                                 One of Never, PreemptLowerPriority.
                                                 Defaults to PreemptLowerPriority if unset.
                                             type: string
+                                        preferSameNode:
+                                            description: |-
+                                                Whether to prefer the same node as the main pod for the additional pod.
+                                                This is useful for pods that are not part of the main pod's deployment, but should still be co-located.
+                                            type: boolean
                                         priority:
                                             description: |-
                                                 The priority value. Various system components use this field to find the

internal/fullnode/pod_builder.go

@@ -560,6 +560,8 @@ func buildAdditionalPod(
 	labels := defaultLabels(crd)
 	labels[kube.NameLabel] = appName(crd) + "-" + podSpec.Name
 
+	belongsTo := instanceName(crd, ordinal)
+
 	pod := &corev1.Pod{
 		TypeMeta: metav1.TypeMeta{
 			Kind:       "Pod",
@@ -574,12 +576,30 @@ func buildAdditionalPod(
 		Spec: podSpec.PodSpec,
 	}
 
+	if podSpec.PreferSameNode {
+		pod.Spec.Affinity = &corev1.Affinity{
+			PodAffinity: &corev1.PodAffinity{
+				PreferredDuringSchedulingIgnoredDuringExecution: []corev1.WeightedPodAffinityTerm{
+					{
+						Weight: 100,
+						PodAffinityTerm: corev1.PodAffinityTerm{
+							LabelSelector: &metav1.LabelSelector{
+								MatchLabels: map[string]string{
+									kube.InstanceLabel: belongsTo,
+								},
+							},
+							TopologyKey: "kubernetes.io/hostname",
+						},
+					},
+				},
+			},
+		}
+	}
+
 	// Apply common labels and annotations
 	preserveMergeInto(pod.Labels, podSpec.Metadata.Labels)
 	preserveMergeInto(pod.Annotations, podSpec.Metadata.Annotations)
 
-	belongsTo := instanceName(crd, ordinal)
-
 	pod.Labels[kube.InstanceLabel] = name
 	pod.Labels[kube.BelongsToLabel] = belongsTo