Check if more than 1 existing bucket is configured

lib/plugins/aws/package/compile/events/s3/index.js

@@ -208,6 +208,7 @@ class AwsCompileS3Events {
 
     service.getAllFunctions().forEach(functionName => {
       let numEventsForFunc = 0;
+      let currentBucketName = null;
       let funcUsesExistingS3Bucket = false;
       const functionObj = service.getFunction(functionName);
       const FunctionName = functionObj.name;
@@ -221,6 +222,17 @@ class AwsCompileS3Events {
             const notificationEvent = event.s3.event || 's3:ObjectCreated:*';
             funcUsesExistingS3Bucket = true;
 
+            if (!currentBucketName) {
+              currentBucketName = bucket;
+            }
+            if (bucket !== currentBucketName) {
+              const errorMessage = [
+                'Only one S3 Bucket can be configured per function.',
+                ` In "${FunctionName}" you're attempting to configure "${currentBucketName}" and "${bucket}" at the same time.`,
+              ].join('');
+              throw new this.serverless.classes.Error(errorMessage);
+            }
+
             rules = _.map(event.s3.rules, rule => {
               const key = Object.keys(rule)[0];
               const value = rule[key];

lib/plugins/aws/package/compile/events/s3/index.test.js

@@ -741,5 +741,29 @@ describe('AwsCompileS3Events', () => {
         });
       });
     });
+
+    it('should throw if more than 1 S3 bucket is configured per function', () => {
+      awsCompileS3Events.serverless.service.functions = {
+        first: {
+          name: 'second',
+          events: [
+            {
+              s3: {
+                bucket: 'existing-s3-bucket',
+                existing: true,
+              },
+            },
+            {
+              s3: {
+                bucket: 'existing-s3-bucket-2',
+                existing: true,
+              },
+            },
+          ],
+        },
+      };
+
+      return expect(() => awsCompileS3Events.existingS3Buckets()).to.throw('Only one S3 Bucket');
+    });
   });
 });