fix(CLI): cdk diff stack deletion causes a race condition

packages/@aws-cdk/cloudformation-diff/lib/diff-template.ts

@@ -37,7 +37,6 @@ const DIFF_HANDLERS: HandlerRegistry = {
  * @param currentTemplate the current state of the stack.
  * @param newTemplate     the target state of the stack.
  * @param changeSet       the change set for this stack.
- * @param isImport        if the stack is importing resources (a migrate stack).
  *
  * @returns a +types.TemplateDiff+ object that represents the changes that will happen if
  *      a stack which current state is described by +currentTemplate+ is updated with
@@ -47,7 +46,6 @@ export function fullDiff(
   currentTemplate: { [key: string]: any },
   newTemplate: { [key: string]: any },
   changeSet?: CloudFormation.DescribeChangeSetOutput,
-  isImport?: boolean,
 ): types.TemplateDiff {
 
   normalize(currentTemplate);
@@ -57,9 +55,6 @@ export function fullDiff(
     filterFalsePositives(theDiff, changeSet);
     addImportInformation(theDiff, changeSet);
   }
-  if (isImport) {
-    addImportInformation(theDiff);
-  }
 
   return theDiff;
 }
@@ -214,25 +209,13 @@ function deepCopy(x: any): any {
   return x;
 }
 
-/**
- * Sets import flag to true for resource imports.
- * When the changeset parameter is not set, the stack is a new migrate stack,
- * so all resource changes are imports.
- */
-function addImportInformation(diff: types.TemplateDiff, changeSet?: CloudFormation.DescribeChangeSetOutput) {
-  if (changeSet) {
-    const imports = findResourceImports(changeSet);
-    diff.resources.forEachDifference((logicalId: string, change: types.ResourceDifference) => {
-      if (imports.includes(logicalId)) {
-        change.isImport = true;
-      }
-    });
-  } else {
-    diff.resources.forEachDifference((logicalId: string, change: types.ResourceDifference) => {
-      logicalId; // dont know how to get past warning that this variable is not used.
+function addImportInformation(diff: types.TemplateDiff, changeSet: CloudFormation.DescribeChangeSetOutput) {
+  const imports = findResourceImports(changeSet);
+  diff.resources.forEachDifference((logicalId: string, change: types.ResourceDifference) => {
+    if (imports.includes(logicalId)) {
       change.isImport = true;
-    });
-  }
+    }
+  });
 }
 
 function filterFalsePositives(diff: types.TemplateDiff, changeSet: CloudFormation.DescribeChangeSetOutput) {

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

@@ -364,7 +364,7 @@ async function uploadBodyParameterAndCreateChangeSet(options: PrepareChangeSetOp
 }
 
 async function createChangeSet(options: CreateChangeSetOptions): Promise<CloudFormation.DescribeChangeSetOutput> {
-  await cleanupOldChangeset(options.exists, options.changeSetName, options.stack.stackName, options.cfn);
+  await cleanupOldChangeset(options.changeSetName, options.stack.stackName, options.cfn);
 
   debug(`Attempting to create ChangeSet with name ${options.changeSetName} for stack ${options.stack.stackName}`);
 
@@ -388,23 +388,16 @@ async function createChangeSet(options: CreateChangeSetOptions): Promise<CloudFo
   debug('Initiated creation of changeset: %s; waiting for it to finish creating...', changeSet.Id);
   // Fetching all pages if we'll execute, so we can have the correct change count when monitoring.
   const createdChangeSet = await waitForChangeSet(options.cfn, options.stack.stackName, options.changeSetName, { fetchAll: options.willExecute });
-  await cleanupOldChangeset(options.exists, options.changeSetName, options.stack.stackName, options.cfn);
+  await cleanupOldChangeset(options.changeSetName, options.stack.stackName, options.cfn);
 
   return createdChangeSet;
 }
 
-export async function cleanupOldChangeset(stackExists: boolean, changeSetName: string, stackName: string, cfn: CloudFormation) {
-  if (stackExists) {
-    // Delete any existing change sets generated by CDK since change set names must be unique.
-    // The delete request is successful as long as the stack exists (even if the change set does not exist).
-    debug(`Removing existing change set with name ${changeSetName} if it exists`);
-    await cfn.deleteChangeSet({ StackName: stackName, ChangeSetName: changeSetName }).promise();
-  } else {
-    // delete the stack since creating a changeset for a stack that doesn't exist leaves that stack in a REVIEW_IN_PROGRESS state
-    // that prevents other changesets from being created, even after the changeset has been deleted.
-    debug(`Removing stack with name ${stackName}`);
-    await cfn.deleteStack({ StackName: stackName }).promise();
-  }
+export async function cleanupOldChangeset(changeSetName: string, stackName: string, cfn: CloudFormation) {
+  // Delete any existing change sets generated by CDK since change set names must be unique.
+  // The delete request is successful as long as the stack exists (even if the change set does not exist).
+  debug(`Removing existing change set with name ${changeSetName} if it exists`);
+  await cfn.deleteChangeSet({ StackName: stackName, ChangeSetName: changeSetName }).promise();
 }
 
 /**

packages/aws-cdk/lib/cdk-toolkit.ts

@@ -136,22 +136,27 @@ export class CdkToolkit {
         throw new Error(`There is no file at ${options.templatePath}`);
       }
 
-      const stackExistsOptions = {
-        stack: stacks.firstStack,
-        deployName: stacks.firstStack.stackName,
-      };
-
-      const stackExists = await this.props.deployments.stackExists(stackExistsOptions);
+      let changeSet = undefined;
 
-      const changeSet = (stackExists && options.changeSet) ? await createDiffChangeSet({
-        stack: stacks.firstStack,
-        uuid: uuid.v4(),
-        willExecute: false,
-        deployments: this.props.deployments,
-        sdkProvider: this.props.sdkProvider,
-        parameters: Object.assign({}, parameterMap['*'], parameterMap[stacks.firstStack.stackName]),
-        stream,
-      }) : undefined;
+      if (options.changeSet) {
+        const stackExists = await this.props.deployments.stackExists({
+          stack: stacks.firstStack,
+          deployName: stacks.firstStack.stackName,
+        });
+        if (stackExists) {
+          changeSet = await createDiffChangeSet({
+            stack: stacks.firstStack,
+            uuid: uuid.v4(),
+            deployments: this.props.deployments,
+            willExecute: false,
+            sdkProvider: this.props.sdkProvider,
+            parameters: Object.assign({}, parameterMap['*'], parameterMap[stacks.firstStack.stackName]),
+            stream,
+          });
+        } else {
+          debug(`the stack '${stacks.firstStack.stackName}' does not exist, skipping changeset creation.`);
+        }
+      }
 
       const template = deserializeStructure(await fs.readFile(options.templatePath, { encoding: 'UTF-8' }));
       diffs = options.securityOnly
@@ -175,36 +180,37 @@ export class CdkToolkit {
           removeNonImportResources(stack);
         }
 
-        const stackExistsOptions = {
-          stack,
-          deployName: stack.stackName,
-        };
+        let changeSet = undefined;
 
-        const stackExists = await this.props.deployments.stackExists(stackExistsOptions);
-
-        // if the stack does not already exist, do not do a changeset
-        // this prevents race conditions between deleting the dummy changeset stack and deploying the real changeset stack
-        // migrate stacks that import resources will not previously exist and default to old diff logic
-        const changeSet = (stackExists && options.changeSet) ? await createDiffChangeSet({
-          stack,
-          uuid: uuid.v4(),
-          deployments: this.props.deployments,
-          willExecute: false,
-          sdkProvider: this.props.sdkProvider,
-          parameters: Object.assign({}, parameterMap['*'], parameterMap[stacks.firstStack.stackName]), // should this be stack?
-          resourcesToImport,
-          stream,
-        }) : undefined;
+        if (options.changeSet) {
+          const stackExists = await this.props.deployments.stackExists({
+            stack: stack,
+            deployName: stack.stackName,
+          });
+          if (stackExists) {
+            changeSet = await createDiffChangeSet({
+              stack,
+              uuid: uuid.v4(),
+              deployments: this.props.deployments,
+              willExecute: false,
+              sdkProvider: this.props.sdkProvider,
+              parameters: Object.assign({}, parameterMap['*'], parameterMap[stacks.firstStack.stackName]),
+              resourcesToImport,
+              stream,
+            });
+          } else {
+            debug(`the stack '${stack.stackName}' does not exist, skipping changeset creation.`);
+          }
+        }
 
         if (resourcesToImport) {
           stream.write('Parameters and rules created during migration do not affect resource configuration.\n');
         }
 
-        // pass a boolean to print if the stack is a migrate stack in order to set all resource diffs to import
         const stackCount =
         options.securityOnly
           ? (numberFromBool(printSecurityDiff(currentTemplate, stack, RequireApproval.Broadening, changeSet)))
-          : (printStackDiff(currentTemplate, stack, strict, contextLines, quiet, changeSet, stream, nestedStacks, !!resourcesToImport));
+          : (printStackDiff(currentTemplate, stack, strict, contextLines, quiet, changeSet, stream, nestedStacks));
 
         diffs += stackCount;
       }

packages/aws-cdk/lib/diff.ts

@@ -26,10 +26,9 @@ export function printStackDiff(
   quiet: boolean,
   changeSet?: CloudFormation.DescribeChangeSetOutput,
   stream: cfnDiff.FormatStream = process.stderr,
-  nestedStackTemplates?: { [nestedStackLogicalId: string]: NestedStackTemplates },
-  isImport?: boolean): number {
+  nestedStackTemplates?: { [nestedStackLogicalId: string]: NestedStackTemplates }): number {
 
-  let diff = cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet, isImport);
+  let diff = cfnDiff.fullDiff(oldTemplate, newTemplate.template, changeSet);
 
   // detect and filter out mangled characters from the diff
   let filteredChangesCount = 0;

packages/aws-cdk/test/diff.test.ts

@@ -67,6 +67,7 @@ describe('imports', () => {
     });
 
     cloudFormation = instanceMockFrom(Deployments);
+    cloudFormation.stackExists = jest.fn().mockReturnValue(Promise.resolve(true));
 
     toolkit = new CdkToolkit({
       cloudExecutable,
@@ -306,6 +307,24 @@ describe('non-nested stacks', () => {
     expect(buffer.data.trim()).not.toContain('There were no differences');
     expect(exitCode).toBe(0);
   });
+
+  test('diff does not check for stack existance when --no-changeset is passed', async () => {
+    // GIVEN
+    const buffer = new StringWritable();
+
+    // WHEN
+    const exitCode = await toolkit.diff({
+      stackNames: ['A', 'A'],
+      stream: buffer,
+      fail: false,
+      quiet: true,
+      changeSet: false,
+    });
+
+    // THEN
+    expect(exitCode).toBe(0);
+    expect(cloudFormation.stackExists).not.toHaveBeenCalled();
+  });
 });
 
 describe('nested stacks', () => {