Azure backend: support snapshots/versioning

backend/remote-state/azure/backend.go

@@ -51,6 +51,13 @@ func New() backend.Backend {
 				DefaultFunc: schema.EnvDefaultFunc("ARM_SAS_TOKEN", ""),
 			},
 
+			"snapshot": {
+				Type:        schema.TypeBool,
+				Optional:    true,
+				Description: "Enable/Disable automatic blob snapshotting",
+				DefaultFunc: schema.EnvDefaultFunc("ARM_SNAPSHOT", false),
+			},
+
 			"resource_group_name": {
 				Type:        schema.TypeString,
 				Optional:    true,
@@ -150,6 +157,7 @@ type Backend struct {
 	containerName string
 	keyName       string
 	accountName   string
+	snapshot      bool
 }
 
 type BackendConfig struct {
@@ -180,6 +188,7 @@ func (b *Backend) configure(ctx context.Context) error {
 	b.containerName = data.Get("container_name").(string)
 	b.accountName = data.Get("storage_account_name").(string)
 	b.keyName = data.Get("key").(string)
+	b.snapshot = data.Get("snapshot").(bool)
 
 	// support for previously deprecated fields
 	clientId := valueFromDeprecatedField(data, "client_id", "arm_client_id")

backend/remote-state/azure/backend_state.go

@@ -90,6 +90,7 @@ func (b *Backend) StateMgr(name string) (state.State, error) {
 		containerName:      b.containerName,
 		keyName:            b.path(name),
 		accountName:        b.accountName,
+		snapshot:           b.snapshot,
 	}
 
 	stateMgr := &remote.State{Client: client}

backend/remote-state/azure/backend_test.go

@@ -21,6 +21,7 @@ func TestBackendConfig(t *testing.T) {
 		"storage_account_name": "tfaccount",
 		"container_name":       "tfcontainer",
 		"key":                  "state",
+		"snapshot":             false,
 		// Access Key must be Base64
 		"access_key": "QUNDRVNTX0tFWQ0K",
 	}
@@ -33,6 +34,9 @@ func TestBackendConfig(t *testing.T) {
 	if b.keyName != "state" {
 		t.Fatalf("Incorrect keyName was populated")
 	}
+	if b.snapshot != false {
+		t.Fatalf("Incorrect snapshot was populated")
+	}
 }
 
 func TestBackendAccessKeyBasic(t *testing.T) {

backend/remote-state/azure/client.go

@@ -5,11 +5,14 @@ import (
 	"encoding/base64"
 	"encoding/json"
 	"fmt"
+	"log"
+
 	"github.com/hashicorp/go-multierror"
 	"github.com/hashicorp/go-uuid"
+	"github.com/tombuildsstuff/giovanni/storage/2018-11-09/blob/blobs"
+
 	"github.com/hashicorp/terraform/state"
 	"github.com/hashicorp/terraform/state/remote"
-	"github.com/tombuildsstuff/giovanni/storage/2018-11-09/blob/blobs"
 )
 
 const (
@@ -24,6 +27,7 @@ type RemoteClient struct {
 	containerName      string
 	keyName            string
 	leaseID            string
+	snapshot           bool
 }
 
 func (c *RemoteClient) Get() (*remote.Payload, error) {
@@ -67,6 +71,18 @@ func (c *RemoteClient) Put(data []byte) error {
 	}
 
 	ctx := context.TODO()
+
+	if c.snapshot {
+		snapshotInput := blobs.SnapshotInput{LeaseID: options.LeaseID}
+
+		log.Printf("[DEBUG] Snapshotting existing Blob %q (Container %q / Account %q)", c.keyName, c.containerName, c.accountName)
+		if _, err := c.giovanniBlobClient.Snapshot(ctx, c.accountName, c.containerName, c.keyName, snapshotInput); err != nil {
+			return fmt.Errorf("error snapshotting Blob %q (Container %q / Account %q): %+v", c.keyName, c.containerName, c.accountName, err)
+		}
+
+		log.Print("[DEBUG] Created blob snapshot")
+	}
+
 	blob, err := c.giovanniBlobClient.GetProperties(ctx, c.accountName, c.containerName, c.keyName, getOptions)
 	if err != nil {
 		if blob.StatusCode != 404 {

website/docs/backends/types/azurerm.html.md

@@ -154,6 +154,8 @@ The following configuration options are supported:
 
 * `environment` - (Optional) The Azure Environment which should be used. This can also be sourced from the `ARM_ENVIRONMENT` environment variable. Possible values are `public`, `china`, `german`, `stack` and `usgovernment`. Defaults to `public`.
 
+* `snapshot` - (Optional) Should the Blob used to store the Terraform Statefile be snapshotted before use? Defaults to `false`. This value can also be sourced from the `ARM_SNAPSHOT` environment variable.
+
 * `endpoint` - (Optional) The Custom Endpoint for Azure Resource Manager. This can also be sourced from the `ARM_ENDPOINT` environment variable.
 
 ~> **NOTE:** An `endpoint` should only be configured when using Azure Stack.