Validate the combination of CloudCompute and BuildConfig

src/lightning_app/CHANGELOG.md

@@ -15,6 +15,10 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Add `--secret` option to CLI to allow binding Secrets to app environment variables when running in the cloud ([#14612](https://github.com/Lightning-AI/lightning/pull/14612))
 
 
+- Added a friendly error message when attempting to run the default cloud compute with a custom base image configured ([#14929](https://github.com/Lightning-AI/lightning/pull/14929))
+
+
+
 ### Changed
 
 -

src/lightning_app/runners/cloud.py

@@ -39,6 +39,7 @@
 )
 from lightning_cloud.openapi.rest import ApiException
 
+from lightning_app import LightningWork
 from lightning_app.core.app import LightningApp
 from lightning_app.core.constants import CLOUD_UPLOAD_WARNING, DISABLE_DEPENDENCY_CACHE
 from lightning_app.runners.backends.cloud import CloudBackend
@@ -112,6 +113,7 @@ def dispatch(
         for flow in self.app.flows:
             for work in flow.works(recurse=False):
                 work_requirements = "\n".join(work.cloud_build_config.requirements)
+                _validate_build_spec_and_compute(work)
                 build_spec = V1BuildSpec(
                     commands=work.cloud_build_config.build_commands(),
                     python_dependencies=V1PythonDependencyInfo(
@@ -361,3 +363,12 @@ def _project_has_sufficient_credits(self, project: V1Membership, app: Optional[L
             balance = 0  # value is missing in some tests
 
         return balance >= 1
+
+
+def _validate_build_spec_and_compute(work: LightningWork) -> None:
+    if work.cloud_build_config.image is not None and work.cloud_compute.name == "default":
+        raise ValueError(
+            f"You requested a custom base image for the Work with name '{work.name}', but custom images are currently"
+            " not supported on the default cloud compute instance. Please choose a different configuration, for example"
+            " `CloudCompute('cpu-medium')`."
+        )

tests/tests_app/runners/test_cloud.py

@@ -30,8 +30,9 @@
     V1Work,
 )
 
-from lightning_app import LightningApp, LightningWork
+from lightning_app import BuildConfig, CloudCompute, LightningApp, LightningFlow, LightningWork
 from lightning_app.runners import backends, cloud
+from lightning_app.runners.cloud import _validate_build_spec_and_compute
 from lightning_app.storage import Drive
 from lightning_app.utilities.cloud import _get_project
 from lightning_app.utilities.dependency_caching import get_hash
@@ -702,3 +703,23 @@ def test_project_has_sufficient_credits():
     for balance, result in credits_and_test_value:
         project = V1Membership(name="test-project1", project_id="test-project-id1", balance=balance)
         assert cloud_runtime._project_has_sufficient_credits(project) is result
+
+
+def test_incompatible_cloud_compute_and_build_config():
+    """Test that an exception is raised when a build config has a custom image defined, but the cloud compute is
+    the default.
+
+    This combination is not supported by the platform.
+    """
+
+    class Work(LightningWork):
+        def __init__(self):
+            super().__init__()
+            self.cloud_compute = CloudCompute(name="default")
+            self.cloud_build_config = BuildConfig(image="custom")
+
+        def run(self):
+            pass
+
+    with pytest.raises(ValueError, match="You requested a custom base image for the Work with name"):
+        _validate_build_spec_and_compute(Work())