fix(events): event bus fails with duplicate policy resource (#28521)

#27340 introduced the ability to create multiple event bus policies on a single event bus. To facilitate this, the logical Id was changed from `"Policy"` to the statementId. This triggers a replacement, which fails in CloudFormation because the statement ID does not change. The idea behind this PR is simple -- we are updating the statement ID of the policy to trigger a change for anyone who updates to the new version.

I think we are okay with this change because no one should be depending on the statementIds of their policies. And since the policy is not a stateful resource, updating the policy should not harm anyone. I have checked the feasibility of this PR on my own, hence the lack of an integ test.

closes #28520 

----

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

packages/@aws-cdk-testing/framework-integ/test/aws-events/test/integ.eventbus.js.snapshot/Stack.template.json

@@ -6,7 +6,7 @@
     "Name": "StackBusAA0A1E4B"
    }
   },
-  "BusStatement1B4D0336C": {
+  "BuscdkStatement1D7D87B9D": {
    "Type": "AWS::Events::EventBusPolicy",
    "Properties": {
     "EventBusName": {
@@ -39,12 +39,12 @@
        "Arn"
       ]
      },
-     "Sid": "Statement1"
+     "Sid": "cdk-Statement1"
     },
-    "StatementId": "Statement1"
+    "StatementId": "cdk-Statement1"
    }
   },
-  "BusStatement2B5FB314B": {
+  "BuscdkStatement2341A5B58": {
    "Type": "AWS::Events::EventBusPolicy",
    "Properties": {
     "EventBusName": {
@@ -77,9 +77,9 @@
        "Arn"
       ]
      },
-     "Sid": "Statement2"
+     "Sid": "cdk-Statement2"
     },
-    "StatementId": "Statement2"
+    "StatementId": "cdk-Statement2"
    }
   }
  },

packages/aws-cdk-lib/aws-events/lib/event-bus.ts

@@ -341,10 +341,13 @@ export class EventBus extends EventBusBase {
       throw new Error('Event Bus policy statements must have a sid');
     }
 
-    const policy = new EventBusPolicy(this, statement.sid, {
+    // In order to generate new statementIDs for the change in https://github.com/aws/aws-cdk/pull/27340
+    const statementId = `cdk-${statement.sid}`.slice(0, 64);
+    statement.sid = statementId;
+    const policy = new EventBusPolicy(this, statementId, {
       eventBus: this,
       statement: statement.toJSON(),
-      statementId: statement.sid,
+      statementId,
     });
 
     return { statementAdded: true, policyDependable: policy };

packages/aws-cdk-lib/aws-events/test/event-bus.test.ts

@@ -548,7 +548,7 @@ describe('event bus', () => {
 
     // THEN
     Template.fromStack(stack).hasResourceProperties('AWS::Events::EventBusPolicy', {
-      StatementId: '123',
+      StatementId: 'cdk-123',
       EventBusName: {
         Ref: 'BusEA82B648',
       },
@@ -569,7 +569,7 @@ describe('event bus', () => {
             ],
           },
         },
-        Sid: '123',
+        Sid: 'cdk-123',
         Resource: {
           'Fn::GetAtt': [
             'BusEA82B648',