refactor: hardcode ScaleError message

We only construct this once in the production code - there's no need to
have it be variable.

Author: iainlane

lambdas/functions/control-plane/src/aws/runners.ts

@@ -213,7 +213,7 @@ async function processFleetResult(
   if (failedCount > 0) {
     logger.warn('Create fleet failed, ScaleError will be thrown to trigger retry for ephemeral runners.');
     logger.debug('Create fleet failed.', { data: fleet.Errors });
-    throw new ScaleError('Failed to create instance, create fleet failed.', failedCount);
+    throw new ScaleError(failedCount);
   }
 
   logger.warn('Create fleet failed, error not recognized as scaling error.', { data: fleet.Errors });

lambdas/functions/control-plane/src/lambda.test.ts

@@ -110,7 +110,7 @@ describe('Test scale up lambda wrapper.', () => {
   });
 
   it('Scale should create a batch failure message', async () => {
-    const error = new ScaleError('Scale should be rejected');
+    const error = new ScaleError();
     const mock = vi.fn() as MockedFunction<typeof scaleUp>;
     mock.mockImplementation(() => {
       return Promise.reject(error);
@@ -242,7 +242,7 @@ describe('Test scale up lambda wrapper.', () => {
       const records = createMultipleRecords(2);
       const multiRecordEvent: SQSEvent = { Records: records };
 
-      const error = new ScaleError('Critical scaling error', 2);
+      const error = new ScaleError(2);
       const mock = vi.fn(scaleUp);
       mock.mockImplementation(() => Promise.reject(error));
       vi.mocked(scaleUp).mockImplementation(mock);

lambdas/functions/control-plane/src/scale-runners/ScaleError.test.ts

@@ -5,15 +5,19 @@ import ScaleError from './ScaleError';
 describe('ScaleError', () => {
   describe('detailedMessage', () => {
     it('should format message for single instance failure', () => {
-      const error = new ScaleError('Failed to create fleet', 1);
+      const error = new ScaleError(1);
 
-      expect(error.detailedMessage).toBe('Failed to create fleet (Failed to create 1 instance)');
+      expect(error.detailedMessage).toBe(
+        'Failed to create instance, create fleet failed. (Failed to create 1 instance)',
+      );
     });
 
     it('should format message for multiple instance failures', () => {
-      const error = new ScaleError('Failed to create fleet', 3);
+      const error = new ScaleError(3);
 
-      expect(error.detailedMessage).toBe('Failed to create fleet (Failed to create 3 instances)');
+      expect(error.detailedMessage).toBe(
+        'Failed to create instance, create fleet failed. (Failed to create 3 instances)',
+      );
     });
   });
 
@@ -56,14 +60,14 @@ describe('ScaleError', () => {
       { failedCount: -1, expected: [], description: 'negative failed instances' },
       { failedCount: -10, expected: [], description: 'large negative failed instances' },
     ])('should handle $description (failedCount=$failedCount)', ({ failedCount, expected }) => {
-      const error = new ScaleError('Test error', failedCount);
+      const error = new ScaleError(failedCount);
       const failures = error.toBatchItemFailures(mockMessages);
 
       expect(failures).toEqual(expected);
     });
 
     it('should handle empty message array', () => {
-      const error = new ScaleError('Test error', 3);
+      const error = new ScaleError(3);
       const failures = error.toBatchItemFailures([]);
 
       expect(failures).toEqual([]);

lambdas/functions/control-plane/src/scale-runners/ScaleError.ts

@@ -2,11 +2,8 @@ import type { SQSBatchItemFailure } from 'aws-lambda';
 import type { ActionRequestMessageSQS } from './scale-up';
 
 class ScaleError extends Error {
-  constructor(
-    message: string,
-    public readonly failedInstanceCount: number = 1,
-  ) {
-    super(message);
+  constructor(public readonly failedInstanceCount: number = 1) {
+    super('Failed to create instance, create fleet failed.');
     this.name = 'ScaleError';
   }