feat: add support for empty directory

api/v1alpha2/minicluster_types.go

@@ -250,6 +250,15 @@ type ContainerVolume struct {
 	// +default=false
 	// +optional
 	ReadOnly bool `json:"readOnly,omitempty"`
+
+	// Add an empty directory custom type
+	// +optional
+	EmptyDirMedium string `json:"emptyDirMedium,omitempty"`
+
+	// +kubebuilder:default=false
+	// +default=false
+	// +optional
+	EmptyDir bool `json:"emptyDir,omitempty"`
 }
 
 type FluxSpec struct {

api/v1alpha2/swagger.json

@@ -121,6 +121,14 @@
           "description": "Config map name if the existing volume is a config map You should also define items if you are using this",
           "type": "string"
         },
+        "emptyDir": {
+          "type": "boolean",
+          "default": false
+        },
+        "emptyDirMedium": {
+          "description": "Add an empty directory custom type",
+          "type": "string"
+        },
         "hostPath": {
           "description": "An existing hostPath to bind to path",
           "type": "string"

chart/templates/minicluster-crd.yaml

@@ -227,6 +227,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string
@@ -720,6 +726,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string

config/crd/bases/flux-framework.org_miniclusters.yaml

@@ -226,6 +226,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string
@@ -723,6 +729,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string

controllers/flux/containers.go

@@ -97,10 +97,21 @@ func getContainers(
 
 		// Add on existing volumes/claims
 		for volumeName, volume := range container.Volumes {
-			mount := corev1.VolumeMount{
-				Name:      volumeName,
-				MountPath: volume.Path,
-				ReadOnly:  volume.ReadOnly,
+
+			var mount corev1.VolumeMount
+			if volume.EmptyDir {
+
+				// We assume bindings to /dev/shm
+				mount = corev1.VolumeMount{
+					Name:      volumeName,
+					MountPath: "/dev/shm",
+				}
+			} else {
+				mount = corev1.VolumeMount{
+					Name:      volumeName,
+					MountPath: volume.Path,
+					ReadOnly:  volume.ReadOnly,
+				}
 			}
 			mounts = append(mounts, mount)
 		}

controllers/flux/volumes.go

@@ -132,11 +132,27 @@ func getExistingVolumes(existing map[string]api.ContainerVolume) []corev1.Volume
 				},
 			}
 
+		} else if volumeMeta.EmptyDir {
+
+			// The Flux Operator supports default and memory
+			medium := corev1.StorageMediumDefault
+			if volumeMeta.EmptyDirMedium == "memory" {
+				medium = corev1.StorageMediumMemory
+			}
+			newVolume = corev1.Volume{
+				Name: volumeName,
+				VolumeSource: corev1.VolumeSource{
+					EmptyDir: &corev1.EmptyDirVolumeSource{
+						Medium: medium,
+					},
+				},
+			}
+
 		} else if volumeMeta.HostPath != "" {
 			newVolume = corev1.Volume{
 				Name: volumeName,
 				VolumeSource: corev1.VolumeSource{
-					// Empath path for type means no checks are done
+					// Empty path for type means no checks are done
 					HostPath: &corev1.HostPathVolumeSource{
 						Path: volumeMeta.Path,
 					},

docs/getting_started/custom-resource-definition.md

@@ -1115,6 +1115,7 @@ We did this because volumes are complex and it was challenging to support every
 the volumes and persistent volume claims that the MiniCluster needs, and simply tell it about them. A volume (that must exist) can be:
 
  - a hostpath (good for local development)
+ - an empty directory (and of a particular custom type, such as Memory)
  - a persistent volume claim (PVC) and persistent volume (PV) that you've created
  - a secret that you've created
  - a config map that you've created
@@ -1171,6 +1172,66 @@ spec:
 
 An example is provided in the [volumes test](https://github.com/flux-framework/flux-operator/tree/main/examples/tests/volumes).
 
+#### emptyDir example
+
+A standard empty directory might look like this:
+
+```yaml
+apiVersion: flux-framework.org/v1alpha2
+kind: MiniCluster
+metadata:
+  name: flux-sample
+spec:
+  size: 2
+  containers:
+    - image: rockylinux:9
+      command: df -h /dev/shm
+      volumes:
+        # must be lowercase!
+        my-empty-dir:
+          emptyDir: true
+```
+
+And one for shared memory (to inherit the host) like this:
+
+
+```yaml
+apiVersion: flux-framework.org/v1alpha2
+kind: MiniCluster
+metadata:
+  name: flux-sample
+spec:
+  size: 2
+  containers:
+    - image: rockylinux:9
+      command: ls /data
+      volumes:
+        # must be lowercase!
+        my-empty-dir:
+          emptyDir: true
+          emptyDirMedium: "memory"
+```
+
+The default binds to the path `/dev/shm` and is not customizable. This can be changed if needed. When you have the "memory" medium added,
+you should see all the shared memory from the host, which is [calculated here](https://github.com/kubernetes/kubernetes/blob/e6616033cb844516b1e91b3ec7cd30f8c5d1ea50/pkg/volume/emptydir/empty_dir.go#L148-L157).
+As an example, here is output from a local run with kind when shared memory is added:
+
+```console
+$ kubectl logs flux-sample-0-smflk 
+Defaulted container "flux-sample" out of: flux-sample, flux-view (init)
+Filesystem      Size  Used Avail Use% Mounted on
+tmpfs            32G     0   32G   0% /dev/shm
+```
+
+And here is the same MiniCluster with the volume removed (64M is the default):
+
+```console
+$ kubectl logs flux-sample-0-4bwjf -f
+Defaulted container "flux-sample" out of: flux-sample, flux-view (init)
+Filesystem      Size  Used Avail Use% Mounted on
+shm              64M     0   64M   0% /dev/shm
+```
+
 #### persistent volume claim example
 
 As an example, the IBM plugin we use to setup takes this approach, and then we define the existing volume on the level of the container:

examples/dist/flux-operator-arm.yaml

@@ -232,6 +232,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string
@@ -729,6 +735,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string

examples/dist/flux-operator.yaml

@@ -232,6 +232,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string
@@ -729,6 +735,12 @@ spec:
                               Config map name if the existing volume is a config map
                               You should also define items if you are using this
                             type: string
+                          emptyDir:
+                            default: false
+                            type: boolean
+                          emptyDirMedium:
+                            description: Add an empty directory custom type
+                            type: string
                           hostPath:
                             description: An existing hostPath to bind to path
                             type: string

examples/tests/emptydir/minicluster-without.yaml

@@ -0,0 +1,13 @@
+apiVersion: flux-framework.org/v1alpha2
+kind: MiniCluster
+metadata:
+  name: flux-sample
+spec:
+  size: 2
+  logging:
+    quiet: true
+
+  # This example shows the default shared memory (64M) without the empty dir
+  containers:
+    - image: rockylinux:9
+      command: df -h /dev/shm

examples/tests/emptydir/minicluster.yaml

@@ -0,0 +1,18 @@
+apiVersion: flux-framework.org/v1alpha2
+kind: MiniCluster
+metadata:
+  name: flux-sample
+spec:
+  size: 2
+  logging:
+    quiet: true
+
+  # This example should show all the shared memory available on the node
+  containers:
+    - image: rockylinux:9
+      command: df -h /dev/shm
+      volumes:
+        # This must be all lowercase!
+        my-empty-dir:
+          emptyDir: true
+          emptyDirMedium: "memory"

sdk/python/v1alpha2/docs/ContainerVolume.md

@@ -6,6 +6,8 @@ Name | Type | Description | Notes
 ------------ | ------------- | ------------- | -------------
 **claim_name** | **str** | Claim name if the existing volume is a PVC | [optional] 
 **config_map_name** | **str** | Config map name if the existing volume is a config map You should also define items if you are using this | [optional] 
+**empty_dir** | **bool** |  | [optional] [default to False]
+**empty_dir_medium** | **str** | Add an empty directory custom type | [optional] 
 **host_path** | **str** | An existing hostPath to bind to path | [optional] 
 **items** | **dict[str, str]** | Items (key and paths) for the config map | [optional] 
 **path** | **str** | Path and claim name are always required if a secret isn't defined | [optional]