From 0fb3e59e0db4b1f44bf444179ed732e9d1a4167e Mon Sep 17 00:00:00 2001
From: Lewis Gaul <lewis.gaul@gmail.com>
Date: Fri, 16 Jun 2023 09:33:54 -0700
Subject: [PATCH 1/3] If route specified in replace_route() doesn't exist then
 return suitable error response

---
 moto/ec2/exceptions.py          |  8 ++++++++
 moto/ec2/models/route_tables.py | 14 +++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/moto/ec2/exceptions.py b/moto/ec2/exceptions.py
index 6eb8d515e..780ed933c 100644
--- a/moto/ec2/exceptions.py
+++ b/moto/ec2/exceptions.py
@@ -444,6 +444,14 @@ class InvalidParameterValueErrorTagSpotFleetRequest(EC2ClientError):
         )
 
 
+class InvalidParameterValueErrorReplaceRoute(EC2ClientError):
+    def __init__(self, cidr: str):
+        super().__init__(
+            "InvalidParameterValue",
+            f"There is no route defined for '{cidr}' in the route table. Use CreateRoute instead.",
+        )
+
+
 class EmptyTagSpecError(EC2ClientError):
     def __init__(self) -> None:
         super().__init__(
diff --git a/moto/ec2/models/route_tables.py b/moto/ec2/models/route_tables.py
index de6217d09..51c8e2e76 100644
--- a/moto/ec2/models/route_tables.py
+++ b/moto/ec2/models/route_tables.py
@@ -18,6 +18,7 @@ from ..exceptions import (
     InvalidRouteTableIdError,
     InvalidAssociationIdError,
     InvalidDestinationCIDRBlockParameterError,
+    InvalidParameterValueErrorReplaceRoute,
     RouteAlreadyExistsError,
     RouteNotSupportedError,
 )
@@ -451,7 +452,18 @@ class RouteBackend:
         route_id = generate_route_id(
             route_table.id, destination_cidr_block, destination_ipv6_cidr_block
         )
-        route = route_table.routes[route_id]
+        try:
+            route = route_table.routes[route_id]
+        except KeyError:
+            cidr = (
+                destination_cidr_block
+                if destination_cidr_block
+                else destination_ipv6_cidr_block
+            )
+            # This should be 'raise InvalidRouteError(route_table_id, cidr)' in
+            # line with the delete_route() equivalent, but for some reason AWS
+            # returns InvalidParameterValue instead in this case.
+            raise InvalidParameterValueErrorReplaceRoute(cidr) from None
 
         route.gateway = None
         route.nat_gateway = None

From b21131c4f6ae04b5cf65a319e45775e0bb2dd11c Mon Sep 17 00:00:00 2001
From: Lewis Gaul <lewis.gaul@gmail.com>
Date: Mon, 19 Jun 2023 07:29:49 -0700
Subject: [PATCH 2/3] Add testcase for replace_route() returning
 InvalidParameterValue error code

---
 tests/test_ec2/test_route_tables.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/tests/test_ec2/test_route_tables.py b/tests/test_ec2/test_route_tables.py
index 70b70bd67..a20e5b68c 100644
--- a/tests/test_ec2/test_route_tables.py
+++ b/tests/test_ec2/test_route_tables.py
@@ -643,6 +643,18 @@ def test_routes_replace():
     ex.value.response["ResponseMetadata"].should.have.key("RequestId")
     ex.value.response["Error"]["Code"].should.equal("InvalidRouteTableID.NotFound")
 
+    with pytest.raises(ClientError) as ex:
+        client.replace_route(
+            RouteTableId=main_route_table.id,
+            DestinationCidrBlock="1.1.1.1/32",
+            NetworkInterfaceId=eni.id,
+        )
+    ex.value.response["ResponseMetadata"]["HTTPStatusCode"].should.equal(400)
+    ex.value.response["ResponseMetadata"].should.have.key("RequestId")
+    # This should be 'InvalidRoute.NotFound' in line with the delete_route()
+    # equivalent, but for some reason AWS returns InvalidParameterValue instead.
+    ex.value.response["Error"]["Code"].should.equal("InvalidParameterValue")
+
 
 @mock_ec2
 def test_routes_already_exist():

From 1d8ca4a8520bebc572a43430ed4feeeec0cefff6 Mon Sep 17 00:00:00 2001
From: Lewis Gaul <lewis.gaul@gmail.com>
Date: Thu, 22 Jun 2023 04:29:05 -0700
Subject: [PATCH 3/3] Use same structure as delete_route() for determining cidr
 string

---
 moto/ec2/models/route_tables.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/moto/ec2/models/route_tables.py b/moto/ec2/models/route_tables.py
index 51c8e2e76..9582f1167 100644
--- a/moto/ec2/models/route_tables.py
+++ b/moto/ec2/models/route_tables.py
@@ -448,6 +448,11 @@ class RouteBackend:
         interface_id: Optional[str] = None,
         vpc_peering_connection_id: Optional[str] = None,
     ) -> Route:
+        cidr = destination_cidr_block
+        if destination_ipv6_cidr_block:
+            cidr = destination_ipv6_cidr_block
+        if destination_prefix_list_id:
+            cidr = destination_prefix_list_id
         route_table = self.get_route_table(route_table_id)
         route_id = generate_route_id(
             route_table.id, destination_cidr_block, destination_ipv6_cidr_block
@@ -455,11 +460,6 @@ class RouteBackend:
         try:
             route = route_table.routes[route_id]
         except KeyError:
-            cidr = (
-                destination_cidr_block
-                if destination_cidr_block
-                else destination_ipv6_cidr_block
-            )
             # This should be 'raise InvalidRouteError(route_table_id, cidr)' in
             # line with the delete_route() equivalent, but for some reason AWS
             # returns InvalidParameterValue instead in this case.