fix(toolkit): 'cdk deploy' support updates to Outputs

packages/aws-cdk/lib/api/deploy-stack.ts

@@ -7,7 +7,7 @@ import { debug, error, print } from '../logging';
 import { toYAML } from '../serialize';
 import { Mode } from './aws-auth/credentials';
 import { ToolkitInfo } from './toolkit-info';
-import { describeStack, stackExists, stackFailedCreating, waitForChangeSet, waitForStack } from './util/cloudformation';
+import { changeSetHasNoChanges, describeStack, stackExists, stackFailedCreating, waitForChangeSet, waitForStack  } from './util/cloudformation';
 import { StackActivityMonitor } from './util/cloudformation/stack-activity-monitor';
 import { StackStatus } from './util/cloudformation/stack-status';
 import { SDK } from './util/sdk';
@@ -77,16 +77,17 @@ export async function deployStack(options: DeployStackOptions): Promise<DeploySt
   }).promise();
   debug('Initiated creation of changeset: %s; waiting for it to finish creating...', changeSet.Id);
   const changeSetDescription = await waitForChangeSet(cfn, deployName, changeSetName);
-  if (!changeSetDescription || !changeSetDescription.Changes || changeSetDescription.Changes.length === 0) {
-    debug('No changes are to be performed on %s, assuming success.', deployName);
+
+  if (changeSetHasNoChanges(changeSetDescription)) {
+    debug('No changes are to be performed on %s.', deployName);
     await cfn.deleteChangeSet({ StackName: deployName, ChangeSetName: changeSetName }).promise();
     return { noOp: true, outputs: await getStackOutputs(cfn, deployName), stackArn: changeSet.StackId! };
   }
 
   debug('Initiating execution of changeset %s on stack %s', changeSetName, deployName);
   await cfn.executeChangeSet({ StackName: deployName, ChangeSetName: changeSetName }).promise();
   // tslint:disable-next-line:max-line-length
-  const monitor = options.quiet ? undefined : new StackActivityMonitor(cfn, deployName, options.stack, changeSetDescription.Changes.length).start();
+  const monitor = options.quiet ? undefined : new StackActivityMonitor(cfn, deployName, options.stack, (changeSetDescription.Changes || []).length).start();
   debug('Execution of changeset %s on stack %s has started; waiting for the update to complete...', changeSetName, deployName);
   await waitForStack(cfn, deployName);
   if (monitor) { await monitor.stop(); }

packages/aws-cdk/lib/api/util/cloudformation.ts

@@ -86,32 +86,53 @@ async function waitFor<T>(valueProvider: () => Promise<T | null | undefined>, ti
 /**
  * Waits for a ChangeSet to be available for triggering a StackUpdate.
  *
+ * Will return a changeset that is either ready to be executed or has no changes.
+ * Will throw in other cases.
+ *
  * @param cfn       a CloudFormation client
  * @param stackName   the name of the Stack that the ChangeSet belongs to
  * @param changeSetName the name of the ChangeSet
  *
  * @returns       the CloudFormation description of the ChangeSet
  */
 // tslint:disable-next-line:max-line-length
-export async function waitForChangeSet(cfn: CloudFormation, stackName: string, changeSetName: string): Promise<CloudFormation.DescribeChangeSetOutput | undefined> {
+export async function waitForChangeSet(cfn: CloudFormation, stackName: string, changeSetName: string): Promise<CloudFormation.DescribeChangeSetOutput> {
   debug('Waiting for changeset %s on stack %s to finish creating...', changeSetName, stackName);
-  return waitFor(async () => {
+  const ret = await waitFor(async () => {
     const description = await describeChangeSet(cfn, stackName, changeSetName);
     // The following doesn't use a switch because tsc will not allow fall-through, UNLESS it is allows
     // EVERYWHERE that uses this library directly or indirectly, which is undesirable.
     if (description.Status === 'CREATE_PENDING' || description.Status === 'CREATE_IN_PROGRESS') {
       debug('Changeset %s on stack %s is still creating', changeSetName, stackName);
       return undefined;
-    } else if (description.Status === 'CREATE_COMPLETE') {
+    }
+
+    if (description.Status === 'CREATE_COMPLETE' || changeSetHasNoChanges(description)) {
       return description;
-    } else if (description.Status === 'FAILED') {
-      if (description.StatusReason && description.StatusReason.startsWith('The submitted information didn\'t contain changes.')) {
-        return description;
-      }
     }
+
     // tslint:disable-next-line:max-line-length
     throw new Error(`Failed to create ChangeSet ${changeSetName} on ${stackName}: ${description.Status || 'NO_STATUS'}, ${description.StatusReason || 'no reason provided'}`);
   });
+
+  if (!ret) {
+    throw new Error('Change set took too long to be created; aborting');
+  }
+
+  return ret;
+}
+
+/**
+ * Return true if the given change set has no changes
+ *
+ * This must be determined from the status, not the 'Changes' array on the
+ * object; the latter can be empty because no resources were changed, but if
+ * there are changes to Outputs, the change set can still be executed.
+ */
+export function changeSetHasNoChanges(description: CloudFormation.DescribeChangeSetOutput) {
+  return description.Status === 'FAILED'
+      && description.StatusReason
+      && description.StatusReason.startsWith('The submitted information didn\'t contain changes.');
 }
 
 /**