diff --git a/batch/batch/cloud/gcp/driver/create_instance.py b/batch/batch/cloud/gcp/driver/create_instance.py
index 1fa2dc64c43..a09f77d0897 100644
--- a/batch/batch/cloud/gcp/driver/create_instance.py
+++ b/batch/batch/cloud/gcp/driver/create_instance.py
@@ -1,3 +1,4 @@
+from typing import Any
 import os
 import logging
 import base64
@@ -61,7 +62,7 @@ def create_instance_config(
         )
     assert unreserved_disk_storage_gb >= 0
 
-    vm_config = {
+    vm_config: Any = {
         'name': machine_name,
         'machineType': f'projects/{project}/zones/{zone}/machineTypes/{machine_type}',
         'labels': {'role': 'batch2-agent', 'namespace': DEFAULT_NAMESPACE},
diff --git a/batch/batch/cloud/gcp/driver/driver.py b/batch/batch/cloud/gcp/driver/driver.py
index 1149e672bdd..7d8683d4c3c 100644
--- a/batch/batch/cloud/gcp/driver/driver.py
+++ b/batch/batch/cloud/gcp/driver/driver.py
@@ -1,4 +1,4 @@
-from typing import Optional, Set
+from typing import Optional, Set, Dict, Any, List
 
 from hailtop import aiotools
 from hailtop.aiocloud import aiogoogle
@@ -72,8 +72,8 @@ def __init__(self, db: Database, machine_name_prefix: str, task_manager: aiotool
         self.namespace = namespace
 
         self.zone_success_rate = ZoneSuccessRate()
-        self.region_info = None
-        self.zones = []
+        self.region_info: Optional[Dict[str, Dict[str, Any]]] = None
+        self.zones: List[str] = []
 
     async def shutdown(self):
         try:
@@ -91,6 +91,7 @@ def get_zone(self, cores: int, worker_local_ssd_data_disk: bool, worker_pd_ssd_d
         global_live_total_cores_mcpu = self.inst_coll_manager.global_live_total_cores_mcpu
         if global_live_total_cores_mcpu // 1000 < 1_000:
             return self.resource_manager.default_location
+        assert self.region_info is not None  # FIXME: this reveals a race condition: if update_region_quotas does not run before we get_zone this will fail
         return get_zone(self.region_info, self.zone_success_rate, cores, worker_local_ssd_data_disk, worker_pd_ssd_data_disk_size_gb)
 
     async def process_activity_logs(self):
diff --git a/batch/batch/cloud/gcp/driver/resource_manager.py b/batch/batch/cloud/gcp/driver/resource_manager.py
index 0d24698657b..f093ccccc7b 100644
--- a/batch/batch/cloud/gcp/driver/resource_manager.py
+++ b/batch/batch/cloud/gcp/driver/resource_manager.py
@@ -21,13 +21,13 @@
 log = logging.getLogger('resource_manager')
 
 
-def parse_gcp_timestamp(timestamp: Optional[str]) -> Optional[float]:
+def parse_gcp_timestamp(timestamp: Optional[str]) -> Optional[int]:
     if timestamp is None:
         return None
-    return dateutil.parser.isoparse(timestamp).timestamp() * 1000
+    return int(dateutil.parser.isoparse(timestamp).timestamp() * 1000 + 0.5)
 
 
-class GCPResourceManager(CloudResourceManager):
+class GCPResourceManager(CloudResourceManager[GCPInstanceConfig]):
     def __init__(self, driver: 'GCPDriver', compute_client: aiogoogle.GoogleComputeClient, default_location: str):
         self.driver = driver
         self.compute_client = compute_client
@@ -93,6 +93,7 @@ def prepare_vm(self,
 
         zone = location
         if zone is None:
+            assert cores is not None, (cores, zone)
             zone = self.driver.get_zone(cores, worker_local_ssd_data_disk, worker_pd_ssd_data_disk_size_gb)
             if zone is None:
                 return None
diff --git a/batch/batch/cloud/gcp/driver/zones.py b/batch/batch/cloud/gcp/driver/zones.py
index e2105a36da5..8be4dab7213 100644
--- a/batch/batch/cloud/gcp/driver/zones.py
+++ b/batch/batch/cloud/gcp/driver/zones.py
@@ -79,8 +79,12 @@ def compute_zone_weights(region_info: Dict[str, Dict[str, Any]], worker_cores: i
     return weights
 
 
-def get_zone(region_info: Dict[str, Dict[str, Any]], zone_success_rate: ZoneSuccessRate, worker_cores: int,
-             worker_local_ssd_data_disk: bool, worker_pd_ssd_data_disk_size_gb: int) -> Optional[str]:
+def get_zone(region_info: Dict[str, Dict[str, Any]],
+             zone_success_rate: ZoneSuccessRate,
+             worker_cores: int,
+             worker_local_ssd_data_disk: bool,
+             worker_pd_ssd_data_disk_size_gb: int
+             ) -> Optional[str]:
     zone_weights = compute_zone_weights(region_info, worker_cores, worker_local_ssd_data_disk, worker_pd_ssd_data_disk_size_gb)
 
     if not zone_weights:
diff --git a/batch/batch/cloud/gcp/instance_config.py b/batch/batch/cloud/gcp/instance_config.py
index 95d82c43593..87914df3e41 100644
--- a/batch/batch/cloud/gcp/instance_config.py
+++ b/batch/batch/cloud/gcp/instance_config.py
@@ -1,4 +1,4 @@
-from typing import List, Optional, Dict, Any
+from typing import List, Optional, Dict, Any, cast
 from typing_extensions import Literal
 from mypy_extensions import TypedDict
 import re
@@ -16,11 +16,15 @@
 
 def parse_machine_type_str(name: str) -> Dict[str, str]:
     match = MACHINE_TYPE_REGEX.fullmatch(name)
+    if match is None:
+        raise ValueError(f'invalid machine type string: {name}')
     return match.groupdict()
 
 
 def parse_disk_type(name: str) -> Dict[str, str]:
     match = DISK_TYPE_REGEX.fullmatch(name)
+    if match is None:
+        raise ValueError(f'invalid disk type string: {name}')
     return match.groupdict()
 
 
@@ -41,9 +45,16 @@ def parse_disk_type(name: str) -> Dict[str, str]:
 # vm_config: Dict[str, Any]
 
 
+disk_type_strs = {'pd-ssd', 'pd-standard', 'local-ssd'}
 DiskType = Literal['pd-ssd', 'pd-standard', 'local-ssd']
 
 
+def assert_valid_disk_type(disk_type: str) -> DiskType:
+    if disk_type in disk_type_strs:
+        return cast(DiskType, disk_type)
+    raise ValueError(f'invalid disk type: {disk_type}')
+
+
 class Disk(TypedDict):
     boot: bool
     project: Optional[str]
@@ -64,7 +75,7 @@ def from_vm_config(vm_config: Dict[str, Any], job_private: bool = False) -> 'GCP
         for disk_config in vm_config['disks']:
             params = disk_config['initializeParams']
             disk_info = parse_disk_type(params['diskType'])
-            disk_type = disk_info['disk_type']
+            disk_type = assert_valid_disk_type(disk_info['disk_type'])
 
             if disk_type == 'local-ssd':
                 disk_size = 375
@@ -199,7 +210,7 @@ def resources(self, cpu_in_mcpu: int, memory_in_bytes: int, storage_in_gib: int)
         # storage is in units of MiB
         resources.append({'name': 'disk/pd-ssd/1', 'quantity': storage_in_gib * 1024})
 
-        quantities = defaultdict(lambda: 0)
+        quantities: Dict[str, int] = defaultdict(lambda: 0)
         for disk in self.disks:
             name = f'disk/{disk["type"]}/1'
             # the factors of 1024 cancel between GiB -> MiB and fraction_1024 -> fraction
diff --git a/batch/batch/cloud/gcp/resource_utils.py b/batch/batch/cloud/gcp/resource_utils.py
index 9e0286b1248..d8a7f944280 100644
--- a/batch/batch/cloud/gcp/resource_utils.py
+++ b/batch/batch/cloud/gcp/resource_utils.py
@@ -29,6 +29,8 @@
 
 def gcp_machine_type_to_dict(machine_type: str) -> Optional[Dict[str, Any]]:
     match = MACHINE_TYPE_REGEX.fullmatch(machine_type)
+    if match is None:
+        return match
     return match.groupdict()
 
 
diff --git a/batch/batch/cloud/worker_utils.py b/batch/batch/cloud/worker_utils.py
index eb08b713042..9d609abdc36 100644
--- a/batch/batch/cloud/worker_utils.py
+++ b/batch/batch/cloud/worker_utils.py
@@ -1,17 +1,20 @@
-from typing import Dict, TYPE_CHECKING
+from typing import Dict
 
-from .gcp.worker.disk import GCPDisk
 from .gcp.worker.credentials import GCPUserCredentials
+from .gcp.worker.disk import GCPDisk
 from .gcp.instance_config import GCPInstanceConfig
 
-if TYPE_CHECKING:
-    from ..worker.disk import CloudDisk  # pylint: disable=cyclic-import
-    from ..worker.credentials import CloudUserCredentials  # pylint: disable=cyclic-import
-    from ..instance_config import InstanceConfig  # pylint: disable=cyclic-import
+from ..worker.credentials import CloudUserCredentials
+from ..worker.disk import CloudDisk
+from ..instance_config import InstanceConfig
 
 
-def get_cloud_disk(instance_name: str, disk_name: str, size_in_gb: int, mount_path: str,
-                   instance_config: 'InstanceConfig') -> 'CloudDisk':
+def get_cloud_disk(instance_name: str,
+                   disk_name: str,
+                   size_in_gb: int,
+                   mount_path: str,
+                   instance_config: InstanceConfig
+                   ) -> CloudDisk:
     cloud = instance_config.cloud
     assert cloud == 'gcp'
     assert isinstance(instance_config, GCPInstanceConfig)
@@ -26,6 +29,6 @@ def get_cloud_disk(instance_name: str, disk_name: str, size_in_gb: int, mount_pa
     return disk
 
 
-def get_user_credentials(cloud: str, credentials: Dict[str, bytes]) -> 'CloudUserCredentials':
+def get_user_credentials(cloud: str, credentials: Dict[str, bytes]) -> CloudUserCredentials:
     assert cloud == 'gcp'
     return GCPUserCredentials(credentials)
diff --git a/batch/batch/driver/instance.py b/batch/batch/driver/instance.py
index 62b24a89fd8..10cb91b9480 100644
--- a/batch/batch/driver/instance.py
+++ b/batch/batch/driver/instance.py
@@ -5,7 +5,6 @@
 import humanize
 import base64
 import json
-from typing import Optional
 
 from hailtop.utils import time_msecs, time_msecs_str, retry_transient_errors
 from hailtop import httpx
@@ -101,10 +100,10 @@ def __init__(
         free_cores_mcpu,
         time_created,
         failed_request_count,
-        last_updated,
+        last_updated: int,
         ip_address,
         version,
-        instance_config: Optional[InstanceConfig],
+        instance_config: InstanceConfig,
     ):
         self.db: Database = app['db']
         self.client_session: httpx.ClientSession = app['client_session']
diff --git a/batch/batch/driver/resource_manager.py b/batch/batch/driver/resource_manager.py
index d04545676f3..4244460d6e8 100644
--- a/batch/batch/driver/resource_manager.py
+++ b/batch/batch/driver/resource_manager.py
@@ -1,10 +1,8 @@
+from typing import Optional, Any, TypeVar, Generic
 import abc
 import logging
-from typing import TYPE_CHECKING, Optional, Any
 
-if TYPE_CHECKING:
-    from ..instance_config import InstanceConfig
-    from .instance import Instance  # pylint: disable=cyclic-import
+from .instance import Instance
 
 
 log = logging.getLogger('compute_manager')
@@ -26,7 +24,10 @@ def __init__(self, state: str, full_spec: Any, last_state_change_timestamp_msecs
         self.last_state_change_timestamp_msecs = last_state_change_timestamp_msecs
 
 
-class CloudResourceManager(abc.ABC):
+T = TypeVar('T')
+
+
+class CloudResourceManager(Generic[T]):
     default_location: str
 
     @abc.abstractmethod
@@ -44,17 +45,17 @@ def prepare_vm(self,
                    worker_type: Optional[str] = None,
                    cores: Optional[int] = None,
                    location: Optional[str] = None,
-                   ) -> Optional['InstanceConfig']:
+                   ) -> Optional[T]:
         pass
 
     @abc.abstractmethod
-    async def create_vm(self, instance_config: 'InstanceConfig'):
+    async def create_vm(self, instance_config: T):
         pass
 
     @abc.abstractmethod
-    async def delete_vm(self, instance: 'Instance'):
+    async def delete_vm(self, instance: Instance):
         pass
 
     @abc.abstractmethod
-    async def get_vm_state(self, instance: 'Instance') -> VMState:
+    async def get_vm_state(self, instance: Instance) -> VMState:
         pass
diff --git a/batch/batch/instance_config.py b/batch/batch/instance_config.py
index 0c72af628e0..e5b19e32883 100644
--- a/batch/batch/instance_config.py
+++ b/batch/batch/instance_config.py
@@ -17,10 +17,16 @@ class InstanceConfig(abc.ABC):
     data_disk_size_gb: int
     job_private: bool
     worker_type: str
-    machine_type: str
-    location: str
     config: Dict[str, Any]
 
+    @property
+    def machine_type(self) -> str:
+        raise NotImplementedError
+
+    @property
+    def location(self) -> str:
+        raise NotImplementedError
+
     @abc.abstractmethod
     def resources(self, cpu_in_mcpu, memory_in_bytes, storage_in_gib):
         pass
diff --git a/batch/batch/worker/credentials.py b/batch/batch/worker/credentials.py
index 780916f7173..eba5cc6b8e1 100644
--- a/batch/batch/worker/credentials.py
+++ b/batch/batch/worker/credentials.py
@@ -9,7 +9,10 @@ class CloudUserCredentials(abc.ABC):
     cloud_env_name: str
     hail_env_name: str
     username: str
-    password: str
+
+    @property
+    def password(self) -> str:
+        raise NotImplementedError
 
     @property
     def mount_path(self):
diff --git a/batch/batch/worker/worker.py b/batch/batch/worker/worker.py
index 5a1f7d59912..27fef415c5b 100644
--- a/batch/batch/worker/worker.py
+++ b/batch/batch/worker/worker.py
@@ -1076,7 +1076,7 @@ def credentials_host_file_path(self):
     @staticmethod
     def create(batch_id,
                user,
-               credentials: Optional[Dict[str, str]],
+               credentials: CloudUserCredentials,
                job_spec: dict,
                format_version: BatchFormatVersion,
                task_manager: aiotools.BackgroundTaskManager,