Adding ignore_changes lifecycle meta property

config/config.go

@@ -84,8 +84,9 @@ type Resource struct {
 // ResourceLifecycle is used to store the lifecycle tuning parameters
 // to allow customized behavior
 type ResourceLifecycle struct {
- CreateBeforeDestroy bool `mapstructure:"create_before_destroy"`
- PreventDestroy bool `mapstructure:"prevent_destroy"`
+ CreateBeforeDestroy bool `mapstructure:"create_before_destroy"`
+ PreventDestroy bool `mapstructure:"prevent_destroy"`
+ IgnoreChanges []string `mapstructure:"ignore_changes"`
 }
 
 // Provisioner is a configured provisioner step on a resource.

config/loader_test.go

@@ -440,6 +440,54 @@ func TestLoadFile_createBeforeDestroy(t *testing.T) {
  }
 }
 
+func TestLoadFile_ignoreChanges(t *testing.T) {
+ c, err := LoadFile(filepath.Join(fixtureDir, "ignore-changes.tf"))
+ if err != nil {
+ t.Fatalf("err: %s", err)
+ }
+
+ if c == nil {
+ t.Fatal("config should not be nil")
+ }
+
+ actual := resourcesStr(c.Resources)
+ print(actual)
+ if actual != strings.TrimSpace(ignoreChangesResourcesStr) {
+ 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 populate ignore changes
+ if len(r.Lifecycle.IgnoreChanges) == 0 {
+ t.Fatalf("Bad: %#v", r)
+ }
+
+ r = c.Resources[1]
+ if r.Name != "bar" && r.Type != "aws_instance" {
+ t.Fatalf("Bad: %#v", r)
+ }
+
+ // Should not populate ignore changes
+ if len(r.Lifecycle.IgnoreChanges) > 0 {
+ t.Fatalf("Bad: %#v", r)
+ }
+
+ r = c.Resources[2]
+ if r.Name != "baz" && r.Type != "aws_instance" {
+ t.Fatalf("Bad: %#v", r)
+ }
+
+ // Should not populate ignore changes
+ if len(r.Lifecycle.IgnoreChanges) > 0 {
+ t.Fatalf("Bad: %#v", r)
+ }
+}
+
 func TestLoad_preventDestroyString(t *testing.T) {
  c, err := LoadFile(filepath.Join(fixtureDir, "prevent-destroy-string.tf"))
  if err != nil {
@@ -676,3 +724,12 @@ aws_instance[bar] (x1)
 aws_instance[web] (x1)
  ami
 `
+
+const ignoreChangesResourcesStr = `
+aws_instance[bar] (x1)
+ ami
+aws_instance[baz] (x1)
+ ami
+aws_instance[web] (x1)
+ ami
+`

config/test-fixtures/ignore-changes.tf

@@ -0,0 +1,17 @@
+resource "aws_instance" "web" {
+ ami = "foo"
+ lifecycle {
+ ignore_changes = ["ami"]
+ }
+}
+
+resource "aws_instance" "bar" {
+ ami = "foo"
+ lifecycle {
+ ignore_changes = []
+ }
+}
+
+resource "aws_instance" "baz" {
+ ami = "foo"
+}

terraform/eval_ignore_changes.go

@@ -0,0 +1,33 @@
+package terraform
+import (
+ "github.com/hashicorp/terraform/config"
+ "strings"
+)
+
+// EvalIgnoreChanges is an EvalNode implementation that removes diff
+// attributes if their name matches names provided by the resource's
+// IgnoreChanges lifecycle.
+type EvalIgnoreChanges struct {
+ Resource *config.Resource
+ Diff **InstanceDiff
+}
+
+func (n *EvalIgnoreChanges) Eval(ctx EvalContext) (interface{}, error) {
+ if n.Diff == nil || *n.Diff == nil || n.Resource == nil || n.Resource.Id() == "" {
+ return nil, nil
+ }
+
+ diff := *n.Diff
+ ignoreChanges := n.Resource.Lifecycle.IgnoreChanges
+
+ for _, ignoredName := range ignoreChanges {
+ for name := range diff.Attributes {
+ if strings.HasPrefix(name, ignoredName) {
+ delete(diff.Attributes, name)
+ diff.Attributes[name].GoString()
+ }
+ }
+ }
+
+ return nil, nil
+}

terraform/transform_resource.go

@@ -318,6 +318,10 @@ func (n *graphNodeExpandedResource) EvalTree() EvalNode {
  Resource: n.Resource,
  Diff: &diff,
  },
+ &EvalIgnoreChanges{
+ Resource: n.Resource,
+ Diff: &diff,
+ },
  &EvalWriteState{
  Name: n.stateId(),
  ResourceType: n.Resource.Type,

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

@@ -68,11 +68,20 @@ The `lifecycle` block allows the following keys to be set:
  destruction of a given resource. When this is set to `true`, any plan
  that includes a destroy of this resource will return an error message.
 
+ * `ignore_changes` (list of strings) - Customizes how diffs are evaluated for
+ resources, allowing individual attributes to be ignored through changes.
+ As an example, this can be used to ignore dynamic changes to the
+ resource from external resources. Other meta-parameters cannot be ignored.
+
 ~> **NOTE on create\_before\_destroy and dependencies:** Resources that utilize
 the `create_before_destroy` key can only depend on other resources that also
 include `create_before_destroy`. Referencing a resource that does not include
 `create_before_destroy` will result in a dependency graph cycle. 
 
+~> **NOTE on ignore\_changes:** Ignored attribute names can be matched by their
+name, not state ID. For example, if an `aws_route_table` has two routes defined
+and the `ignore_changes` list contains "route", both routes will be ignored.
+
 -------------
 
 Within a resource, you can optionally have a **connection block**.
@@ -191,6 +200,8 @@ where `LIFECYCLE` is:
 ```
 lifecycle {
  [create_before_destroy = true|false]
+ [prevent_destroy = true|false]
+ [ignore_changes = [ATTRIBUTE NAME, ...]]
 }
 ```