EC2: validate pagination parameters (#6293)

moto/ec2/responses/instances.py

@@ -14,6 +14,12 @@ from ._base_response import EC2BaseResponse
 class InstanceResponse(EC2BaseResponse):
     def describe_instances(self) -> str:
         self.error_on_dryrun()
+        # https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/ec2/client/describe_instances.html
+        # You cannot specify this(MaxResults) parameter and the instance IDs parameter in the same request.
+        if "InstanceId.1" in self.data and "MaxResults" in self.data:
+            raise InvalidParameterCombination(
+                "The parameter instancesSet cannot be used with the parameter maxResults"
+            )
         filter_dict = self._filters_from_querystring()
         instance_ids = self._get_multi_param("InstanceId")
         token = self._get_param("NextToken")

tests/test_ec2/test_instances.py

@@ -318,23 +318,46 @@ def test_get_paginated_instances():
         instances.extend(
             conn.create_instances(ImageId=EXAMPLE_AMI_ID, MinCount=1, MaxCount=1)
         )
-    instance_ids = [i.id for i in instances]
 
-    resp1 = client.describe_instances(InstanceIds=instance_ids, MaxResults=5)
+    resp1 = client.describe_instances(MaxResults=5)
     res1 = resp1["Reservations"]
     res1.should.have.length_of(5)
     next_token = resp1["NextToken"]
 
     next_token.should_not.equal(None)
 
-    resp2 = client.describe_instances(InstanceIds=instance_ids, NextToken=next_token)
-    resp2["Reservations"].should.have.length_of(7)  # 12 total - 5 from the first call
-    assert "NextToken" not in resp2  # This is it - no more pages
+    resp2 = client.describe_instances(NextToken=next_token)
+
+    # at least 12 total - 5 from the first call but there may be more from servermode tests
+    assert len(resp2["Reservations"]) >= 7
 
     for i in instances:
         i.terminate()
 
 
+@mock_ec2
+def test_describe_instances_pagination_error():
+    client = boto3.client("ec2", region_name="us-east-1")
+
+    # Call describe_instances with a bad id should raise an error
+    with pytest.raises(ClientError) as ex:
+        paginator = client.get_paginator("describe_instances").paginate(
+            InstanceIds=["i-12345678"],
+            PaginationConfig={
+                "MaxItems": 9999,
+                "PageSize": 100,
+            },
+        )
+        for page in paginator:
+            dir(page)
+
+    assert ex.value.response["Error"]["Code"] == "InvalidParameterCombination"
+    assert (
+        ex.value.response["Error"]["Message"]
+        == "The parameter instancesSet cannot be used with the parameter maxResults"
+    )
+
+
 @mock_ec2
 def test_create_with_tags():
     ec2 = boto3.client("ec2", region_name="us-west-2")