Log when downloading a preload script (#4094)

distributed/preloading.py

@@ -120,6 +120,7 @@ def _import_module(name, file_dir=None) -> ModuleType:
 
 
 async def _download_module(url: str) -> ModuleType:
+    logger.info("Downloading preload at %s", url)
     assert is_webaddress(url)
 
     client = AsyncHTTPClient()

distributed/tests/test_preload.py

@@ -9,7 +9,7 @@
 
 import dask
 from distributed import Client, Scheduler, Worker, Nanny
-from distributed.utils_test import cluster
+from distributed.utils_test import cluster, captured_logger
 from distributed.utils_test import loop, cleanup  # noqa F401
 
 
@@ -139,7 +139,9 @@ def dask_setup(dask_server):
     app = web.Application([(r"/preload", MyHandler)])
     server = app.listen(12345)
     try:
-        async with Scheduler(preload=["http://localhost:12345/preload"]) as s:
-            assert s.foo == 1
+        with captured_logger("distributed.preloading") as log:
+            async with Scheduler(preload=["http://localhost:12345/preload"]) as s:
+                assert s.foo == 1
+        assert "12345/preload" in log.getvalue()
     finally:
         server.stop()