Merge pull request #12173 from hashicorp/b-remote-state-ds

providers/terraform: remote state data source supports backends

backend/init/init.go

@@ -0,0 +1,69 @@
+// Package init contains the list of backends that can be initialized and
+// basic helper functions for initializing those backends.
+package init
+
+import (
+	"sync"
+
+	"github.com/hashicorp/terraform/backend"
+
+	backendlegacy "github.com/hashicorp/terraform/backend/legacy"
+	backendlocal "github.com/hashicorp/terraform/backend/local"
+	backendconsul "github.com/hashicorp/terraform/backend/remote-state/consul"
+	backendinmem "github.com/hashicorp/terraform/backend/remote-state/inmem"
+)
+
+// backends is the list of available backends. This is a global variable
+// because backends are currently hardcoded into Terraform and can't be
+// modified without recompilation.
+//
+// To read an available backend, use the Backend function. This ensures
+// safe concurrent read access to the list of built-in backends.
+//
+// Backends are hardcoded into Terraform because the API for backends uses
+// complex structures and supporting that over the plugin system is currently
+// prohibitively difficult. For those wanting to implement a custom backend,
+// they can do so with recompilation.
+var backends map[string]func() backend.Backend
+var backendsLock sync.Mutex
+
+func init() {
+	// Our hardcoded backends. We don't need to acquire a lock here
+	// since init() code is serial and can't spawn goroutines.
+	backends = map[string]func() backend.Backend{
+		"local":  func() backend.Backend { return &backendlocal.Local{} },
+		"consul": func() backend.Backend { return backendconsul.New() },
+		"inmem":  func() backend.Backend { return backendinmem.New() },
+	}
+
+	// Add the legacy remote backends that haven't yet been convertd to
+	// the new backend API.
+	backendlegacy.Init(backends)
+}
+
+// Backend returns the initialization factory for the given backend, or
+// nil if none exists.
+func Backend(name string) func() backend.Backend {
+	backendsLock.Lock()
+	defer backendsLock.Unlock()
+	return backends[name]
+}
+
+// Set sets a new backend in the list of backends. If f is nil then the
+// backend will be removed from the map. If this backend already exists
+// then it will be overwritten.
+//
+// This method sets this backend globally and care should be taken to do
+// this only before Terraform is executing to prevent odd behavior of backends
+// changing mid-execution.
+func Set(name string, f func() backend.Backend) {
+	backendsLock.Lock()
+	defer backendsLock.Unlock()
+
+	if f == nil {
+		delete(backends, name)
+		return
+	}
+
+	backends[name] = f
+}

builtin/providers/terraform/data_source_state.go

@@ -1,11 +1,14 @@
 package terraform
 
 import (
+	"fmt"
 	"log"
 	"time"
 
+	backendinit "github.com/hashicorp/terraform/backend/init"
+	"github.com/hashicorp/terraform/config"
 	"github.com/hashicorp/terraform/helper/schema"
-	"github.com/hashicorp/terraform/state/remote"
+	"github.com/hashicorp/terraform/terraform"
 )
 
 func dataSourceRemoteState() *schema.Resource {
@@ -43,9 +46,11 @@ func dataSourceRemoteState() *schema.Resource {
 
 func dataSourceRemoteStateRead(d *schema.ResourceData, meta interface{}) error {
 	backend := d.Get("backend").(string)
-	config := make(map[string]string)
-	for k, v := range d.Get("config").(map[string]interface{}) {
-		config[k] = v.(string)
+
+	// Get the configuration in a type we want.
+	rawConfig, err := config.NewRawConfig(d.Get("config").(map[string]interface{}))
+	if err != nil {
+		return fmt.Errorf("error initializing backend: %s", err)
 	}
 
 	// Don't break people using the old _local syntax - but note warning above
@@ -55,15 +60,23 @@ func dataSourceRemoteStateRead(d *schema.ResourceData, meta interface{}) error {
 	}
 
 	// Create the client to access our remote state
-	log.Printf("[DEBUG] Initializing remote state client: %s", backend)
-	client, err := remote.NewClient(backend, config)
-	if err != nil {
-		return err
+	log.Printf("[DEBUG] Initializing remote state backend: %s", backend)
+	f := backendinit.Backend(backend)
+	if f == nil {
+		return fmt.Errorf("Unknown backend type: %s", backend)
 	}
+	b := f()
 
-	// Create the remote state itself and refresh it in order to load the state
-	log.Printf("[DEBUG] Loading remote state...")
-	state := &remote.State{Client: client}
+	// Configure the backend
+	if err := b.Configure(terraform.NewResourceConfig(rawConfig)); err != nil {
+		return fmt.Errorf("error initializing backend: %s", err)
+	}
+
+	// Get the state
+	state, err := b.State()
+	if err != nil {
+		return fmt.Errorf("error loading the remote state: %s", err)
+	}
 	if err := state.RefreshState(); err != nil {
 		return err
 	}

builtin/providers/terraform/data_source_state_test.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"testing"
 
+	backendinit "github.com/hashicorp/terraform/backend/init"
 	"github.com/hashicorp/terraform/helper/resource"
 	"github.com/hashicorp/terraform/terraform"
 )
@@ -24,6 +25,25 @@ func TestState_basic(t *testing.T) {
 	})
 }
 
+func TestState_backends(t *testing.T) {
+	backendinit.Set("_ds_test", backendinit.Backend("local"))
+	defer backendinit.Set("_ds_test", nil)
+
+	resource.UnitTest(t, resource.TestCase{
+		PreCheck:  func() { testAccPreCheck(t) },
+		Providers: testAccProviders,
+		Steps: []resource.TestStep{
+			{
+				Config: testAccState_backend,
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckStateValue(
+						"data.terraform_remote_state.foo", "foo", "bar"),
+				),
+			},
+		},
+	})
+}
+
 func TestState_complexOutputs(t *testing.T) {
 	resource.UnitTest(t, resource.TestCase{
 		PreCheck:  func() { testAccPreCheck(t) },
@@ -72,6 +92,15 @@ data "terraform_remote_state" "foo" {
 	}
 }`
 
+const testAccState_backend = `
+data "terraform_remote_state" "foo" {
+	backend = "_ds_test"
+
+	config {
+		path = "./test-fixtures/basic.tfstate"
+	}
+}`
+
 const testAccState_complexOutputs = `
 resource "terraform_remote_state" "foo" {
 	backend = "local"

command/meta_backend.go

@@ -16,6 +16,7 @@ import (
 	"github.com/hashicorp/go-multierror"
 	"github.com/hashicorp/hcl"
 	"github.com/hashicorp/terraform/backend"
+	backendinit "github.com/hashicorp/terraform/backend/init"
 	clistate "github.com/hashicorp/terraform/command/state"
 	"github.com/hashicorp/terraform/config"
 	"github.com/hashicorp/terraform/state"
@@ -24,8 +25,6 @@ import (
 
 	backendlegacy "github.com/hashicorp/terraform/backend/legacy"
 	backendlocal "github.com/hashicorp/terraform/backend/local"
-	backendconsul "github.com/hashicorp/terraform/backend/remote-state/consul"
-	backendinmem "github.com/hashicorp/terraform/backend/remote-state/inmem"
 )
 
 // BackendOpts are the options used to initialize a backend.Backend.
@@ -1149,8 +1148,8 @@ func (m *Meta) backend_C_r_S_unchanged(
 	config := terraform.NewResourceConfig(rawC)
 
 	// Get the backend
-	f, ok := Backends[s.Backend.Type]
-	if !ok {
+	f := backendinit.Backend(s.Backend.Type)
+	if f == nil {
 		return nil, fmt.Errorf(strings.TrimSpace(errBackendSavedUnknown), s.Backend.Type)
 	}
 	b := f()
@@ -1300,8 +1299,8 @@ func (m *Meta) backendInitFromConfig(c *config.Backend) (backend.Backend, error)
 	config := terraform.NewResourceConfig(c.RawConfig)
 
 	// Get the backend
-	f, ok := Backends[c.Type]
-	if !ok {
+	f := backendinit.Backend(c.Type)
+	if f == nil {
 		return nil, fmt.Errorf(strings.TrimSpace(errBackendNewUnknown), c.Type)
 	}
 	b := f()
@@ -1374,8 +1373,8 @@ func (m *Meta) backendInitFromSaved(s *terraform.BackendState) (backend.Backend,
 	config := terraform.NewResourceConfig(rawC)
 
 	// Get the backend
-	f, ok := Backends[s.Type]
-	if !ok {
+	f := backendinit.Backend(s.Type)
+	if f == nil {
 		return nil, fmt.Errorf(strings.TrimSpace(errBackendSavedUnknown), s.Type)
 	}
 	b := f()
@@ -1397,27 +1396,6 @@ func (m *Meta) backendInitRequired(reason string) {
 // Output constants and initialization code
 //-------------------------------------------------------------------
 
-// Backends is the list of available backends. This is currently a hardcoded
-// list that can't be modified without recompiling Terraform. This is done
-// because the API for backends uses complex structures and supporting that
-// over the plugin system is currently prohibitively difficult. For those
-// wanting to implement a custom backend, recompilation should not be a
-// high barrier.
-var Backends map[string]func() backend.Backend
-
-func init() {
-	// Our hardcoded backends
-	Backends = map[string]func() backend.Backend{
-		"local":  func() backend.Backend { return &backendlocal.Local{} },
-		"consul": func() backend.Backend { return backendconsul.New() },
-		"inmem":  func() backend.Backend { return backendinmem.New() },
-	}
-
-	// Add the legacy remote backends that haven't yet been convertd to
-	// the new backend API.
-	backendlegacy.Init(Backends)
-}
-
 // errBackendInitRequired is the final error message shown when reinit
 // is required for some reason. The error message includes the reason.
 var errBackendInitRequired = errors.New(