Fixed redundant multiple mounting clusters

Fixes #445

Author: nfx

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## 0.3.0
 
+* Fixed redundant multiple mounting clusters ([#445](https://github.com/databrickslabs/terraform-provider-databricks/issues/445))
 * Added optional parameter azure_environment to provider config which defaults to public ([#437](https://github.com/databrickslabs/terraform-provider-databricks/pull/437)).
 * Added [databricks_service_principal](https://github.com/databrickslabs/terraform-provider-databricks/pull/386) resource.
 * `skip_validation` from `databricks_instance_profile` was removed and is always set to `true`.

compute/clusters.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"sort"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/databrickslabs/databricks-terraform/common"
@@ -293,8 +294,16 @@ func (a ClustersAPI) ListNodeTypes() (l NodeTypeList, err error) {
 	return
 }
 
+// getOrCreateClusterMutex guards "mounting" cluster creation to prevent multiple
+// redundant instances created at the same name. Compute package private property.
+// https://github.com/databrickslabs/terraform-provider-databricks/issues/445
+var getOrCreateClusterMutex sync.Mutex
+
 // GetOrCreateRunningCluster creates an autoterminating cluster if it doesn't exist
 func (a ClustersAPI) GetOrCreateRunningCluster(name string, custom ...Cluster) (c ClusterInfo, err error) {
+	getOrCreateClusterMutex.Lock()
+	defer getOrCreateClusterMutex.Unlock()
+
 	if len(custom) > 1 {
 		err = fmt.Errorf("You can only specify 1 custom cluster conf, not %d", len(custom))
 		return

storage/mounts.go

@@ -112,11 +112,16 @@ func getMountingClusterID(ctx context.Context, client *common.DatabricksClient,
 		r := compute.Cluster{
 			NumWorkers:  0,
 			ClusterName: "terraform-mount",
-			SparkVersion: clustersAPI.LatestSparkVersionOrDefault(compute.SparkVersionRequest{
-				Latest:          true,
-				LongTermSupport: true,
-			}),
-			NodeTypeID:             clustersAPI.GetSmallestNodeType(compute.NodeTypeRequest{LocalDisk: true}),
+			SparkVersion: clustersAPI.LatestSparkVersionOrDefault(
+				compute.SparkVersionRequest{
+					Latest:          true,
+					LongTermSupport: true,
+				}),
+			NodeTypeID: clustersAPI.GetSmallestNodeType(
+				compute.NodeTypeRequest{
+					LocalDisk: true,
+				}),
+
 			AutoterminationMinutes: 10,
 			SparkConf: map[string]string{
 				"spark.master":                     "local[*]",