for people who are interested, the above exception should be caused by the following reason:

I think this is something due to how dagsterweb got packed. it got packed into a .pyz with gunicorn + Flask app inside as a standalone app, so yes, at the very beginning, it indeed get booted up via /export/apps/python/3.7/bin/python3.7 , that is why at the running time, we see /export/apps/python/3.7/bin/python3.7 being sys.executable; however, that super-long site-packages directory is dynamically added into the sys.path, which means at running time, dagster libs can be located successfully within the same process; but since we are using sys.executable to execute another app, we are out of luck.
the only solution i could think of is to install dagster lib into the site packages of /export/apps/python/3.7/bin/python3.7 , but that would be ugly as typically it would cumbersome to install a lib on the host without going through the build & deploy pipeline.