Merge pull request #317 from hashicorp/f-create-before

Adding support for `lifecycle` and `create_before_destroy`

config/config.go

@@ -60,6 +60,13 @@ type Resource struct {
 	RawConfig    *RawConfig
 	Provisioners []*Provisioner
 	DependsOn    []string
+	Lifecycle    ResourceLifecycle
+}
+
+// ResourceLifecycle is used to store the lifecycle tuning parameters
+// to allow customized behavior
+type ResourceLifecycle struct {
+	CreateBeforeDestroy bool `hcl:"create_before_destroy"`
 }
 
 // Provisioner is a configured provisioner step on a resource.

config/loader_hcl.go

@@ -394,6 +394,7 @@ func loadResourcesHcl(os *hclobj.Object) ([]*Resource, error) {
 			delete(config, "count")
 			delete(config, "depends_on")
 			delete(config, "provisioner")
+			delete(config, "lifecycle")
 
 			rawConfig, err := NewRawConfig(config)
 			if err != nil {
@@ -457,6 +458,20 @@ func loadResourcesHcl(os *hclobj.Object) ([]*Resource, error) {
 				}
 			}
 
+			// Check if the resource should be re-created before
+			// destroying the existing instance
+			var lifecycle ResourceLifecycle
+			if o := obj.Get("lifecycle", false); o != nil {
+				err = hcl.DecodeObject(&lifecycle, o)
+				if err != nil {
+					return nil, fmt.Errorf(
+						"Error parsing lifecycle for %s[%s]: %s",
+						t.Key,
+						k,
+						err)
+				}
+			}
+
 			result = append(result, &Resource{
 				Name:         k,
 				Type:         t.Key,
@@ -464,6 +479,7 @@ func loadResourcesHcl(os *hclobj.Object) ([]*Resource, error) {
 				RawConfig:    rawConfig,
 				Provisioners: provisioners,
 				DependsOn:    dependsOn,
+				Lifecycle:    lifecycle,
 			})
 		}
 	}

config/loader_test.go

@@ -346,6 +346,43 @@ func TestLoad_connections(t *testing.T) {
 	}
 }
 
+func TestLoad_createBeforeDestroy(t *testing.T) {
+	c, err := Load(filepath.Join(fixtureDir, "create-before-destroy.tf"))
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	if c == nil {
+		t.Fatal("config should not be nil")
+	}
+
+	actual := resourcesStr(c.Resources)
+	if actual != strings.TrimSpace(createBeforeDestroyResourcesStr) {
+		t.Fatalf("bad:\n%s", actual)
+	}
+
+	// Check for the flag value
+	r := c.Resources[0]
+	if r.Name != "web" && r.Type != "aws_instance" {
+		t.Fatalf("Bad: %#v", r)
+	}
+
+	// Should enable create before destroy
+	if !r.Lifecycle.CreateBeforeDestroy {
+		t.Fatalf("Bad: %#v", r)
+	}
+
+	r = c.Resources[1]
+	if r.Name != "bar" && r.Type != "aws_instance" {
+		t.Fatalf("Bad: %#v", r)
+	}
+
+	// Should not enable create before destroy
+	if r.Lifecycle.CreateBeforeDestroy {
+		t.Fatalf("Bad: %#v", r)
+	}
+}
+
 const basicOutputsStr = `
 web_ip
   vars
@@ -523,3 +560,10 @@ foo (required)
   <>
   <>
 `
+
+const createBeforeDestroyResourcesStr = `
+aws_instance[bar] (x1)
+  ami
+aws_instance[web] (x1)
+  ami
+`

config/test-fixtures/create-before-destroy.tf

@@ -0,0 +1,14 @@
+
+resource "aws_instance" "web" {
+    ami = "foo"
+    lifecycle {
+        create_before_destroy = true
+    }
+}
+
+resource "aws_instance" "bar" {
+    ami = "foo"
+    lifecycle {
+        create_before_destroy = false
+    }
+}

depgraph/graph.go

@@ -357,3 +357,23 @@ func (g *Graph) Walk(fn WalkFunc) error {
 		return err
 	}
 }
+
+// DependsOn returns the set of nouns that have a
+// dependency on a given noun. This can be used to find
+// the incoming edges to a noun.
+func (g *Graph) DependsOn(n *Noun) []*Noun {
+	var incoming []*Noun
+OUTER:
+	for _, other := range g.Nouns {
+		if other == n {
+			continue
+		}
+		for _, d := range other.Deps {
+			if d.Target == n {
+				incoming = append(incoming, other)
+				continue OUTER
+			}
+		}
+	}
+	return incoming
+}

depgraph/graph_test.go

@@ -429,3 +429,39 @@ g -> h`)
 		}
 	}
 }
+
+func TestGraph_DependsOn(t *testing.T) {
+	nodes := ParseNouns(`a -> b
+a -> c
+b -> d
+b -> e
+c -> d
+c -> e`)
+
+	g := &Graph{
+		Name:  "Test",
+		Nouns: NounMapToList(nodes),
+	}
+
+	dNoun := g.Noun("d")
+	incoming := g.DependsOn(dNoun)
+
+	if len(incoming) != 2 {
+		t.Fatalf("bad: %#v", incoming)
+	}
+
+	var hasB, hasC bool
+	for _, in := range incoming {
+		switch in.Name {
+		case "b":
+			hasB = true
+		case "c":
+			hasC = true
+		default:
+			t.Fatalf("Bad: %#v", in)
+		}
+	}
+	if !hasB || !hasC {
+		t.Fatalf("missing incoming edge")
+	}
+}

terraform/context.go

@@ -1264,17 +1264,46 @@ func (c *walkContext) persistState(r *Resource) {
 	rs.Dependencies = r.Dependencies
 
 	// Assign the instance state to the proper location
-	if r.Flags&FlagTainted != 0 {
+	if r.Flags&FlagDeposed != 0 {
+		// We were previously the primary and have been deposed, so
+		// now we are the final tainted resource
+		r.TaintedIndex = len(rs.Tainted) - 1
+		rs.Tainted[r.TaintedIndex] = r.State
+
+	} else if r.Flags&FlagTainted != 0 {
 		if r.TaintedIndex >= 0 {
 			// Tainted with a pre-existing index, just update that spot
 			rs.Tainted[r.TaintedIndex] = r.State
+
+		} else if r.Flags&FlagReplacePrimary != 0 {
+			// We just replaced the primary, so restore the primary
+			rs.Primary = rs.Tainted[len(rs.Tainted)-1]
+
+			// Set ourselves as tainted
+			rs.Tainted[len(rs.Tainted)-1] = r.State
+
 		} else {
 			// Newly tainted, so append it to the list, update the
 			// index, and remove the primary.
 			rs.Tainted = append(rs.Tainted, r.State)
-			rs.Primary = nil
 			r.TaintedIndex = len(rs.Tainted) - 1
+			rs.Primary = nil
 		}
+
+	} else if r.Flags&FlagReplacePrimary != 0 {
+		// If the ID is blank (there was an error), then we leave
+		// the primary that exists, and do not store this as a tainted
+		// instance
+		if r.State.ID == "" {
+			return
+		}
+
+		// Push the old primary into the tainted state
+		rs.Tainted = append(rs.Tainted, rs.Primary)
+
+		// Set this as the new primary
+		rs.Primary = r.State
+
 	} else {
 		// The primary instance, so just set it directly
 		rs.Primary = r.State

terraform/context_test.go

@@ -582,6 +582,58 @@ func TestContextApply(t *testing.T) {
 	}
 }
 
+func TestContextApply_createBeforeDestroy(t *testing.T) {
+	m := testModule(t, "apply-good-create-before")
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.bar": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"require_new": "abc",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State: state,
+	})
+
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	mod := state.RootModule()
+	if len(mod.Resources) != 1 {
+		t.Fatalf("bad: %#v", mod.Resources)
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyCreateBeforeStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s", actual)
+	}
+}
+
 func TestContextApply_Minimal(t *testing.T) {
 	m := testModule(t, "apply-minimal")
 	p := testProvider("aws")
@@ -880,6 +932,168 @@ func TestContextApply_provisionerFail(t *testing.T) {
 	}
 }
 
+func TestContextApply_provisionerFail_createBeforeDestroy(t *testing.T) {
+	m := testModule(t, "apply-provisioner-fail-create-before")
+	p := testProvider("aws")
+	pr := testProvisioner()
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	pr.ApplyFn = func(*InstanceState, *ResourceConfig) error {
+		return fmt.Errorf("EXPLOSION")
+	}
+
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.bar": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"require_new": "abc",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		Provisioners: map[string]ResourceProvisionerFactory{
+			"shell": testProvisionerFuncFixed(pr),
+		},
+		State: state,
+	})
+
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := ctx.Apply()
+	if err == nil {
+		t.Fatal("should error")
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyProvisionerFailCreateBeforeDestroyStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s", actual)
+	}
+}
+
+func TestContextApply_error_createBeforeDestroy(t *testing.T) {
+	m := testModule(t, "apply-error-create-before")
+	p := testProvider("aws")
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.bar": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"require_new": "abc",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State: state,
+	})
+	p.ApplyFn = func(info *InstanceInfo, is *InstanceState, id *InstanceDiff) (*InstanceState, error) {
+		return nil, fmt.Errorf("error")
+	}
+	p.DiffFn = testDiffFn
+
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := ctx.Apply()
+	if err == nil {
+		t.Fatal("should have error")
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyErrorCreateBeforeDestroyStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s\n\n\n%s", actual, expected)
+	}
+}
+
+func TestContextApply_errorDestroy_createBeforeDestroy(t *testing.T) {
+	m := testModule(t, "apply-error-create-before")
+	p := testProvider("aws")
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.bar": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"require_new": "abc",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State: state,
+	})
+	p.ApplyFn = func(info *InstanceInfo, is *InstanceState, id *InstanceDiff) (*InstanceState, error) {
+		// Fail the destroy!
+		if id.Destroy {
+			return is, fmt.Errorf("error")
+		}
+
+		// Create should work
+		is = &InstanceState{
+			ID: "foo",
+		}
+		return is, nil
+	}
+	p.DiffFn = testDiffFn
+
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	state, err := ctx.Apply()
+	if err == nil {
+		t.Fatal("should have error")
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyErrorDestroyCreateBeforeDestroyStr)
+	if actual != expected {
+		t.Fatalf("bad: actual:\n%s\n\nexpected:\n%s", actual, expected)
+	}
+}
+
 func TestContextApply_provisionerResourceRef(t *testing.T) {
 	m := testModule(t, "apply-provisioner-resource-ref")
 	p := testProvider("aws")
@@ -1698,6 +1912,85 @@ func TestContextApply_vars(t *testing.T) {
 	}
 }
 
+func TestContextApply_createBefore_depends(t *testing.T) {
+	m := testModule(t, "apply-depends-create-before")
+	h := new(HookRecordApplyOrder)
+	p := testProvider("aws")
+	p.ApplyFn = testApplyFn
+	p.DiffFn = testDiffFn
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.web": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"require_new": "ami-old",
+							},
+						},
+					},
+					"aws_instance.lb": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "baz",
+							Attributes: map[string]string{
+								"instance": "bar",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	ctx := testContext(t, &ContextOpts{
+		Module: m,
+		Hooks:  []Hook{h},
+		Providers: map[string]ResourceProviderFactory{
+			"aws": testProviderFuncFixed(p),
+		},
+		State: state,
+	})
+
+	if _, err := ctx.Plan(nil); err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	h.Active = true
+	state, err := ctx.Apply()
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	mod := state.RootModule()
+	if len(mod.Resources) < 2 {
+		t.Fatalf("bad: %#v", mod.Resources)
+	}
+
+	actual := strings.TrimSpace(state.String())
+	expected := strings.TrimSpace(testTerraformApplyDependsCreateBeforeStr)
+	if actual != expected {
+		t.Fatalf("bad: \n%s\n%s", actual, expected)
+	}
+
+	// Test that things were managed _in the right order_
+	order := h.States
+	diffs := h.Diffs
+	if order[0].ID != "bar" || diffs[0].Destroy {
+		t.Fatalf("should create new instance first: %#v", order)
+	}
+
+	if order[1].ID != "baz" {
+		t.Fatalf("update must happen after create: %#v", order)
+	}
+
+	if order[2].ID != "bar" || !diffs[2].Destroy {
+		t.Fatalf("destroy must happen after update: %#v", order)
+	}
+}
+
 func TestContextPlan(t *testing.T) {
 	m := testModule(t, "plan-good")
 	p := testProvider("aws")
@@ -3121,6 +3414,9 @@ func testDiffFn(
 			New: v.(string),
 		}
 
+		if k == "require_new" {
+			attrDiff.RequiresNew = true
+		}
 		diff.Attributes[k] = attrDiff
 	}
 

terraform/graph.go

@@ -299,6 +299,15 @@ func graphEncodeDependencies(g *depgraph.Graph) {
 		}
 		r := rn.Resource
 
+		// If we are using create-before-destroy, there
+		// are some special depedencies injected on the
+		// deposed node that would cause a circular depedency
+		// chain if persisted. We must only handle the new node,
+		// node the deposed node.
+		if r.Flags&FlagDeposed != 0 {
+			continue
+		}
+
 		// Update the dependencies
 		var inject []string
 		for _, dep := range n.Deps {
@@ -482,6 +491,7 @@ func graphAddConfigResources(
 // these nodes for you.
 func graphAddDiff(g *depgraph.Graph, d *ModuleDiff) error {
 	var nlist []*depgraph.Noun
+	injected := make(map[*depgraph.Dependency]struct{})
 	for _, n := range g.Nouns {
 		rn, ok := n.Meta.(*GraphNodeResource)
 		if !ok {
@@ -530,13 +540,70 @@ func graphAddDiff(g *depgraph.Graph, d *ModuleDiff) error {
 			newDiff.Destroy = false
 			rd = newDiff
 
-			// Add to the new noun to our dependencies so that the destroy
-			// happens before the apply.
-			n.Deps = append(n.Deps, &depgraph.Dependency{
+			// The dependency ordering depends on if the CreateBeforeDestroy
+			// flag is enabled. If so, we must create the replacement first,
+			// and then destroy the old instance.
+			if rn.Config != nil && rn.Config.Lifecycle.CreateBeforeDestroy && !rd.Empty() {
+				dep := &depgraph.Dependency{
+					Name:   n.Name,
+					Source: newN,
+					Target: n,
+				}
+
+				// Add the old noun to the new noun dependencies so that
+				// the create happens before the destroy.
+				newN.Deps = append(newN.Deps, dep)
+
+				// Mark that this dependency has been injected so that
+				// we do not invert the direction below.
+				injected[dep] = struct{}{}
+
+				// Add a depedency from the root, since the create node
+				// does not depend on us
+				g.Root.Deps = append(g.Root.Deps, &depgraph.Dependency{
+					Name:   newN.Name,
+					Source: g.Root,
+					Target: newN,
+				})
+
+				// Set the ReplacePrimary flag on the new instance so that
+				// it will become the new primary, and Diposed flag on the
+				// existing instance so that it will step down
+				rn.Resource.Flags |= FlagReplacePrimary
+				newNode.Resource.Flags |= FlagDeposed
+
+				// This logic is not intuitive, but we need to make the
+				// destroy depend upon any resources that depend on the
+				// create. The reason is suppose you have a LB depend on
+				// a web server. You need the order to be create, update LB,
+				// destroy. Without this, the update LB and destroy can
+				// be executed in an arbitrary order (likely in parallel).
+				incoming := g.DependsOn(n)
+				for _, inc := range incoming {
+					// Ignore the root...
+					if inc == g.Root {
+						continue
+					}
+					dep := &depgraph.Dependency{
+						Name:   inc.Name,
+						Source: newN,
+						Target: inc,
+					}
+					injected[dep] = struct{}{}
+					newN.Deps = append(newN.Deps, dep)
+				}
+
+			} else {
+				dep := &depgraph.Dependency{
 					Name:   newN.Name,
 					Source: n,
 					Target: newN,
-			})
+				}
+
+				// Add the new noun to our dependencies so that
+				// the destroy happens before the apply.
+				n.Deps = append(n.Deps, dep)
+			}
 		}
 
 		rn.Resource.Diff = rd
@@ -544,7 +611,6 @@ func graphAddDiff(g *depgraph.Graph, d *ModuleDiff) error {
 
 	// Go through each noun and make sure we calculate all the dependencies
 	// properly.
-	injected := make(map[*depgraph.Dependency]struct{})
 	for _, n := range nlist {
 		deps := n.Deps
 		num := len(deps)
@@ -948,6 +1014,7 @@ func graphAddRoot(g *depgraph.Graph) {
 		})
 	}
 	g.Nouns = append(g.Nouns, root)
+	g.Root = root
 }
 
 // graphAddVariableDeps inspects all the nouns and adds any dependencies

terraform/graph_test.go

@@ -652,6 +652,81 @@ func TestGraphAddDiff_module(t *testing.T) {
 	}
 }
 
+func TestGraphAddDiff_createBeforeDestroy(t *testing.T) {
+	m := testModule(t, "graph-diff-create-before")
+	diff := &Diff{
+		Modules: []*ModuleDiff{
+			&ModuleDiff{
+				Path: rootModulePath,
+				Resources: map[string]*InstanceDiff{
+					"aws_instance.bar": &InstanceDiff{
+						Destroy: true,
+						Attributes: map[string]*ResourceAttrDiff{
+							"ami": &ResourceAttrDiff{
+								Old:         "abc",
+								New:         "xyz",
+								RequiresNew: true,
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+	state := &State{
+		Modules: []*ModuleState{
+			&ModuleState{
+				Path: rootModulePath,
+				Resources: map[string]*ResourceState{
+					"aws_instance.bar": &ResourceState{
+						Type: "aws_instance",
+						Primary: &InstanceState{
+							ID: "bar",
+							Attributes: map[string]string{
+								"ami": "abc",
+							},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	diffHash := checksumStruct(t, diff)
+
+	g, err := Graph(&GraphOpts{
+		Module: m,
+		Diff:   diff,
+		State:  state,
+	})
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+
+	actual := strings.TrimSpace(g.String())
+	expected := strings.TrimSpace(testTerraformGraphDiffCreateBeforeDestroyStr)
+	if actual != expected {
+		t.Fatalf("bad:\n\n%s\n\nexpected:\n\n%s", actual, expected)
+	}
+
+	// Verify the flags are set
+	r := g.Noun("aws_instance.bar")
+	if r.Meta.(*GraphNodeResource).Resource.Flags&FlagReplacePrimary == 0 {
+		t.Fatalf("missing FlagReplacePrimary")
+	}
+
+	r = g.Noun("aws_instance.bar (destroy)")
+	if r.Meta.(*GraphNodeResource).Resource.Flags&FlagDeposed == 0 {
+		t.Fatalf("missing FlagDeposed")
+	}
+
+	// Verify that our original structure has not been modified
+	diffHash2 := checksumStruct(t, diff)
+	if diffHash != diffHash2 {
+		t.Fatal("diff has been modified")
+	}
+}
+
 func TestGraphAddDiff_moduleDestroy(t *testing.T) {
 	m := testModule(t, "graph-diff-module")
 	diff := &Diff{
@@ -1044,8 +1119,19 @@ aws_load_balancer.weblb
   aws_load_balancer.weblb -> provider.aws
 provider.aws
 root
-  root -> aws_load_balancer.weblb
-`
+  root -> aws_load_balancer.weblb`
+
+const testTerraformGraphDiffCreateBeforeDestroyStr = `
+root: root
+aws_instance.bar
+  aws_instance.bar -> provider.aws
+aws_instance.bar (destroy)
+  aws_instance.bar (destroy) -> aws_instance.bar
+  aws_instance.bar (destroy) -> provider.aws
+provider.aws
+root
+  root -> aws_instance.bar
+  root -> aws_instance.bar (destroy)`
 
 const testTerraformGraphStateStr = `
 root: root

terraform/resource.go

@@ -47,6 +47,8 @@ const (
 	FlagTainted
 	FlagOrphan
 	FlagHasTainted
+	FlagReplacePrimary
+	FlagDeposed
 )
 
 // InstanceInfo is used to hold information about the instance and/or

terraform/terraform_test.go

@@ -150,6 +150,27 @@ aws_instance.foo:
   type = aws_instance
 `
 
+const testTerraformApplyDependsCreateBeforeStr = `
+aws_instance.lb:
+  ID = foo
+  instance = foo
+  type = aws_instance
+
+  Dependencies:
+    aws_instance.web
+aws_instance.web:
+  ID = foo
+  require_new = ami-new
+  type = aws_instance
+`
+
+const testTerraformApplyCreateBeforeStr = `
+aws_instance.bar:
+  ID = foo
+  require_new = xyz
+  type = aws_instance
+`
+
 const testTerraformApplyCancelStr = `
 aws_instance.foo:
   ID = foo
@@ -218,6 +239,13 @@ aws_instance.foo:
   type = aws_instance
 `
 
+const testTerraformApplyProvisionerFailCreateBeforeDestroyStr = `
+aws_instance.bar: (1 tainted)
+  ID = bar
+  require_new = abc
+  Tainted ID 1 = foo
+`
+
 const testTerraformApplyProvisionerResourceRefStr = `
 aws_instance.bar:
   ID = foo
@@ -247,6 +275,18 @@ aws_instance.foo:
   num = 2
 `
 
+const testTerraformApplyErrorCreateBeforeDestroyStr = `
+aws_instance.bar:
+  ID = bar
+  require_new = abc
+`
+
+const testTerraformApplyErrorDestroyCreateBeforeDestroyStr = `
+aws_instance.bar: (1 tainted)
+  ID = foo
+  Tainted ID 1 = bar
+`
+
 const testTerraformApplyErrorPartialStr = `
 aws_instance.bar:
   ID = bar

terraform/test-fixtures/apply-depends-create-before/main.tf

@@ -0,0 +1,11 @@
+
+resource "aws_instance" "web" {
+    require_new = "ami-new"
+    lifecycle {
+        create_before_destroy = true
+    }
+}
+
+resource "aws_instance" "lb" {
+    instance = "${aws_instance.web.id}"
+}

terraform/test-fixtures/apply-error-create-before/main.tf

@@ -0,0 +1,6 @@
+resource "aws_instance" "bar" {
+    require_new = "xyz"
+    lifecycle {
+        create_before_destroy = true
+    }
+}

terraform/test-fixtures/apply-good-create-before/main.tf

@@ -0,0 +1,6 @@
+resource "aws_instance" "bar" {
+    require_new = "xyz"
+    lifecycle {
+        create_before_destroy = true
+    }
+}

terraform/test-fixtures/apply-provisioner-fail-create-before/main.tf

@@ -0,0 +1,7 @@
+resource "aws_instance" "bar" {
+    require_new = "xyz"
+    provisioner "shell" {}
+    lifecycle {
+        create_before_destroy = true
+    }
+}

terraform/test-fixtures/graph-diff-create-before/main.tf

@@ -0,0 +1,8 @@
+provider "aws" {}
+
+resource "aws_instance" "bar" {
+    ami = "abc"
+    lifecycle {
+        create_before_destroy = true
+    }
+}

website/source/docs/configuration/resources.html.md

@@ -49,6 +49,17 @@ There are **meta-parameters** available to all resources:
       resource. The dependencies are in the format of `TYPE.NAME`,
       for example `aws_instance.web`.
 
+  * `lifecycle` (configuration block) - Customizes the lifecycle
+      behavior of the resource. The specific options are documented
+      below.
+
+The `lifecycle` block allows the following keys to be set:
+
+  * `create_before_destroy` (bool) - This flag is used to ensure
+      the replacement of a resource is created before the original
+      instance is destroyed. As an example, this can be used to
+      create an new DNS record before removing an old record.
+
 -------------
 
 Within a resource, you can optionally have a **connection block**.
@@ -88,6 +99,7 @@ resource TYPE NAME {
 	CONFIG ...
 	[count = COUNT]
     [depends_on = [RESOURCE NAME, ...]]
+    [LIFECYCLE]
 
 	[CONNECTION]
 	[PROVISIONER ...]
@@ -104,6 +116,14 @@ KEY {
 }
 ```
 
+where `LIFECYCLE` is:
+
+```
+lifecycle {
+    [create_before_destroy = true|false]
+}
+```
+
 where `CONNECTION` is:
 
 ```