Adding sidecars to nodepools for any additional functionality

docs/designs/crd.md

@@ -550,6 +550,12 @@ Every NodePool is defining different Opensearch Nodes StatefulSet
         <td>Updates the probes timeouts and thresholds config</td>
         <td>false</td>
         <td>-</td>
+      </tr><tr>
+        <td><b>sidecars</b></td>
+        <td>[]object</td>
+        <td>List of sidecar containers to be attached to the OpenSearch node pods. Each sidecar follows the Kubernetes container spec.</td>
+        <td>false</td>
+        <td>-</td>
       </tr>
 </table>
 

docs/userguide/main.md

@@ -1432,3 +1432,45 @@ spec:
 ```
 
 Note: the `.spec.name` is immutable, meaning that it cannot be changed after the resources have been deployed to a Kubernetes cluster
+
+## Adding sidecar containers
+
+You can add sidecar containers to your OpenSearch node pods. This is useful for running additional services alongside OpenSearch, such as log collectors, metrics exporters, or custom monitoring agents. Here's an example:
+
+```yaml
+apiVersion: opensearch.opster.io/v1
+kind: OpenSearchCluster
+metadata:
+  name: my-cluster
+spec:
+  nodePools:
+    - component: masters
+      replicas: 3
+      diskSize: "5Gi"
+      sidecars:
+        - name: log-collector
+          image: fluent/fluent-bit:latest
+          resources:
+            requests:
+              memory: "64Mi"
+              cpu: "100m"
+            limits:
+              memory: "128Mi"
+              cpu: "200m"
+        - name: metrics-exporter
+          image: prom/node-exporter:latest
+          ports:
+            - containerPort: 9100
+              name: metrics
+```
+
+Each sidecar container follows the standard Kubernetes container specification, allowing you to configure:
+- Container image and version
+- Resource requests and limits
+- Environment variables
+- Volume mounts
+- Ports
+- Command and arguments
+- Security context
+
+Sidecar containers are deployed alongside the OpenSearch containers in the same pod, sharing the same network namespace and allowing for localhost communication.

opensearch-operator/api/v1/opensearch_types.go

@@ -124,6 +124,8 @@ type NodePool struct {
 	PriorityClassName         string                            `json:"priorityClassName,omitempty"`
 	Pdb                       *PdbConfig                        `json:"pdb,omitempty"`
 	Probes                    *ProbesConfig                     `json:"probes,omitempty"`
+	// Sidecars defines the sidecar containers to be added to the nodepool pods
+	Sidecars []corev1.Container `json:"sidecars,omitempty"`
 }
 
 // PersistencConfig defines options for data persistence

opensearch-operator/pkg/builders/cluster.go

@@ -465,7 +465,7 @@ func NewSTSForNodePool(
 					Annotations: annotations,
 				},
 				Spec: corev1.PodSpec{
-					Containers: []corev1.Container{
+					Containers: append([]corev1.Container{
 						{
 							Env: []corev1.EnvVar{
 								{
@@ -523,7 +523,7 @@ func NewSTSForNodePool(
 							VolumeMounts:    volumeMounts,
 							SecurityContext: securityContext,
 						},
-					},
+					}, node.Sidecars...),
 					InitContainers:            initContainers,
 					Volumes:                   volumes,
 					ServiceAccountName:        cr.Spec.General.ServiceAccount,

opensearch-operator/pkg/builders/cluster_test.go

@@ -401,6 +401,49 @@ var _ = Describe("Builders", func() {
 				Value: "-Xmx1024M -Xms1024M -Dopensearch.transport.cname_in_publish_address=true",
 			}))
 		})
+		It("should only use valid roles", func() {
+			clusterObject := ClusterDescWithVersion("2.2.1")
+			result := NewSTSForNodePool("foobar", &clusterObject, opsterv1.NodePool{
+				Roles: []string{"cluster_manager", "data", "invalid"},
+			}, "foobar", nil, nil, nil)
+			Expect(len(result.Spec.Template.Spec.Containers[0].Env)).To(Equal(8))
+			for _, env := range result.Spec.Template.Spec.Containers[0].Env {
+				if env.Name == "node.roles" {
+					Expect(env.Value).To(Equal("cluster_manager,data"))
+				}
+			}
+		})
+		It("should include sidecar containers when specified", func() {
+			clusterObject := ClusterDescWithVersion("2.2.1")
+			sidecar := corev1.Container{
+				Name:  "sidecar",
+				Image: "sidecar:latest",
+			}
+			result := NewSTSForNodePool("foobar", &clusterObject, opsterv1.NodePool{
+				Roles:    []string{"cluster_manager"},
+				Sidecars: []corev1.Container{sidecar},
+			}, "foobar", nil, nil, nil)
+			Expect(len(result.Spec.Template.Spec.Containers)).To(Equal(2))
+			Expect(result.Spec.Template.Spec.Containers[1].Name).To(Equal("sidecar"))
+		})
+		It("should include multiple sidecar containers when specified", func() {
+			clusterObject := ClusterDescWithVersion("2.2.1")
+			sidecar1 := corev1.Container{
+				Name:  "sidecar1",
+				Image: "sidecar1:latest",
+			}
+			sidecar2 := corev1.Container{
+				Name:  "sidecar2",
+				Image: "sidecar2:latest",
+			}
+			result := NewSTSForNodePool("foobar", &clusterObject, opsterv1.NodePool{
+				Roles:    []string{"cluster_manager"},
+				Sidecars: []corev1.Container{sidecar1, sidecar2},
+			}, "foobar", nil, nil, nil)
+			Expect(len(result.Spec.Template.Spec.Containers)).To(Equal(3))
+			Expect(result.Spec.Template.Spec.Containers[1].Name).To(Equal("sidecar1"))
+			Expect(result.Spec.Template.Spec.Containers[2].Name).To(Equal("sidecar2"))
+		})
 	})
 
 	When("Constructing a bootstrap pod", func() {