fix(lambda-event-sources): cannot add sqs event source to an imported…

… function (aws#21970)

If an SQS event sources is added to an imported function it will throw an error if the function is not imported with an IAM role.

This PR updates the logic to only attempt to add permissions to the principal if the role exists, otherwise it will add a warning indicating that permissions were not added.

fixes aws#12607


----

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### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/main/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-lambda-event-sources/lib/sqs.ts

@@ -1,6 +1,6 @@
 import * as lambda from '@aws-cdk/aws-lambda';
 import * as sqs from '@aws-cdk/aws-sqs';
-import { Duration, Names, Token } from '@aws-cdk/core';
+import { Duration, Names, Token, Annotations } from '@aws-cdk/core';
 
 export interface SqsEventSourceProps {
   /**
@@ -84,7 +84,14 @@ export class SqsEventSource implements lambda.IEventSource {
     });
     this._eventSourceMappingId = eventSourceMapping.eventSourceMappingId;
 
-    this.queue.grantConsumeMessages(target);
+    // only grant access if the lambda function has an IAM role
+    // otherwise the IAM module will throw an error
+    if (target.role) {
+      this.queue.grantConsumeMessages(target);
+    } else {
+      Annotations.of(target).addWarning(`Function '${target.node.path}' was imported without an IAM role `+
+        `so it was not granted access to consume messages from '${this.queue.node.path}'`);
+    }
   }
 
   /**

packages/@aws-cdk/aws-lambda-event-sources/test/sqs.test.ts

@@ -1,7 +1,9 @@
 import { Template } from '@aws-cdk/assertions';
+import * as iam from '@aws-cdk/aws-iam';
 import * as lambda from '@aws-cdk/aws-lambda';
 import * as sqs from '@aws-cdk/aws-sqs';
 import * as cdk from '@aws-cdk/core';
+import { App } from '@aws-cdk/core';
 import * as sources from '../lib';
 import { TestFunction } from './test-function';
 
@@ -282,8 +284,115 @@ describe('SQSEventSource', () => {
     Template.fromStack(stack).hasResourceProperties('AWS::Lambda::EventSourceMapping', {
       'FunctionResponseTypes': ['ReportBatchItemFailures'],
     });
+  });
+
+  test('warning added if lambda function imported without role', () => {
+    const app = new App();
+    const stack = new cdk.Stack(app);
+    const fn = lambda.Function.fromFunctionName(stack, 'Handler', 'testFunction');
+    const q = new sqs.Queue(stack, 'Q');
+
+    // WHEN
+    fn.addEventSource(new sources.SqsEventSource(q));
+    const assembly = app.synth();
+
+    const messages = assembly.getStackArtifact(stack.artifactId).messages;
+
+    // THEN
+    expect(messages.length).toEqual(1);
+    expect(messages[0]).toMatchObject({
+      level: 'warning',
+      id: '/Default/Handler',
+      entry: {
+        data: expect.stringMatching(/Function 'Default\/Handler' was imported without an IAM role/),
+      },
+    });
 
+    // THEN
+    Template.fromStack(stack).resourceCountIs('AWS::Lambda::EventSourceMapping', 1);
+    Template.fromStack(stack).resourceCountIs('AWS::IAM::Policy', 0);
+  });
 
+  test('policy added to imported function role', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    const fn = lambda.Function.fromFunctionAttributes(stack, 'Handler', {
+      functionArn: stack.formatArn({
+        service: 'lambda',
+        resource: 'function',
+        resourceName: 'testFunction',
+      }),
+      role: iam.Role.fromRoleName(stack, 'Role', 'testFunctionRole'),
+    });
+    const q = new sqs.Queue(stack, 'Q');
+
+    // WHEN
+    fn.addEventSource(new sources.SqsEventSource(q));
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::IAM::Policy', {
+      'PolicyDocument': {
+        'Statement': [
+          {
+            'Action': [
+              'sqs:ReceiveMessage',
+              'sqs:ChangeMessageVisibility',
+              'sqs:GetQueueUrl',
+              'sqs:DeleteMessage',
+              'sqs:GetQueueAttributes',
+            ],
+            'Effect': 'Allow',
+            'Resource': {
+              'Fn::GetAtt': [
+                'Q63C6E3AB',
+                'Arn',
+              ],
+            },
+          },
+        ],
+        'Version': '2012-10-17',
+      },
+      'Roles': ['testFunctionRole'],
+    });
+
+    Template.fromStack(stack).hasResourceProperties('AWS::Lambda::EventSourceMapping', {
+      'EventSourceArn': {
+        'Fn::GetAtt': [
+          'Q63C6E3AB',
+          'Arn',
+        ],
+      },
+      'FunctionName': {
+        'Fn::Select': [
+          6,
+          {
+            'Fn::Split': [
+              ':',
+              {
+                'Fn::Join': [
+                  '',
+                  [
+                    'arn:',
+                    {
+                      'Ref': 'AWS::Partition',
+                    },
+                    ':lambda:',
+                    {
+                      'Ref': 'AWS::Region',
+                    },
+                    ':',
+                    {
+                      'Ref': 'AWS::AccountId',
+                    },
+                    ':function/testFunction',
+                  ],
+                ],
+              },
+            ],
+          },
+        ],
+      },
+    });
   });
 
   test('adding filter criteria', () => {