Allow empty_dir volume shared across containers in container group

internal/services/containers/container_group_resource.go

@@ -867,6 +867,7 @@ func expandContainerGroupContainers(d *pluginsdk.ResourceData) (*[]containerinst
 	containerInstancePorts := make([]containerinstance.Port, 0)
 	containerGroupPorts := make([]containerinstance.Port, 0)
 	containerGroupVolumes := make([]containerinstance.Volume, 0)
+	addedEmptyDirs := map[string]bool{}
 
 	for _, containerConfig := range containersConfig {
 		data := containerConfig.(map[string]interface{})
@@ -964,7 +965,17 @@ func expandContainerGroupContainers(d *pluginsdk.ResourceData) (*[]containerinst
 			}
 			container.VolumeMounts = volumeMounts
 			if containerGroupVolumesPartial != nil {
-				containerGroupVolumes = append(containerGroupVolumes, *containerGroupVolumesPartial...)
+				for _, cgVol := range *containerGroupVolumesPartial {
+					if cgVol.EmptyDir != nil {
+						if addedEmptyDirs[*cgVol.Name] {
+							// empty_dir-volumes are allowed to overlap across containers, in fact that is their primary purpose,
+							// but the containerGroup must not declare same name of such volumes twice.
+							continue
+						}
+						addedEmptyDirs[*cgVol.Name] = true
+					}
+					containerGroupVolumes = append(containerGroupVolumes, cgVol)
+				}
 			}
 		}
 

internal/services/containers/container_group_resource_test.go

@@ -491,6 +491,21 @@ func TestAccContainerGroup_emptyDirVolume(t *testing.T) {
 	})
 }
 
+func TestAccContainerGroup_emptyDirVolumeShared(t *testing.T) {
+	data := acceptance.BuildTestData(t, "azurerm_container_group", "test")
+	r := ContainerGroupResource{}
+
+	data.ResourceTest(t, r, []acceptance.TestStep{
+		{
+			Config: r.emptyDirVolumeShared(data),
+			Check: acceptance.ComposeTestCheckFunc(
+				check.That(data.ResourceName).ExistsInAzure(r),
+			),
+		},
+		data.ImportStep(),
+	})
+}
+
 func TestAccContainerGroup_secretVolume(t *testing.T) {
 	data := acceptance.BuildTestData(t, "azurerm_container_group", "test")
 	r := ContainerGroupResource{}
@@ -1553,6 +1568,66 @@ resource "azurerm_container_group" "test" {
 `, data.RandomInteger, data.Locations.Primary, data.RandomInteger, data.RandomInteger)
 }
 
+func (ContainerGroupResource) emptyDirVolumeShared(data acceptance.TestData) string {
+	return fmt.Sprintf(`
+provider "azurerm" {
+  features {}
+}
+
+resource "azurerm_resource_group" "test" {
+  name     = "acctestRG-%d"
+  location = "%s"
+}
+
+resource "azurerm_container_group" "test" {
+  name                = "acctestcontainergroupemptyshared-%d"
+  location            = "${azurerm_resource_group.test.location}"
+  resource_group_name = "${azurerm_resource_group.test.name}"
+  ip_address_type     = "public"
+  dns_name_label      = "acctestcontainergroup-%d"
+  os_type             = "Linux"
+  restart_policy      = "Never"
+
+  container {
+    name     = "writer"
+    image    = "ubuntu:20.04"
+    cpu      = "1"
+    memory   = "1.5"
+    commands = ["touch", "/sharedempty/file.txt"]
+
+    # Dummy port not used, workaround for https://github.com/hashicorp/terraform-provider-azurerm/issues/1697
+    ports {
+      port     = 80
+      protocol = "TCP"
+    }
+
+    volume {
+      name       = "logs"
+      mount_path = "/sharedempty"
+      read_only  = false
+      empty_dir  = true
+    }
+  }
+
+  container {
+    name   = "reader"
+    image  = "ubuntu:20.04"
+    cpu    = "1"
+    memory = "1.5"
+
+    volume {
+      name       = "logs"
+      mount_path = "/sharedempty"
+      read_only  = false
+      empty_dir  = true
+    }
+
+    commands = ["/bin/bash", "-c", "timeout 30 watch --interval 1 --errexit \"! cat /sharedempty/file.txt\""]
+  }
+}
+`, data.RandomInteger, data.Locations.Primary, data.RandomInteger, data.RandomInteger)
+}
+
 func (ContainerGroupResource) secretVolume(data acceptance.TestData) string {
 	return fmt.Sprintf(`
 provider "azurerm" {