Move local repo cleanup into worker shutdown.

Making cleanup Gunicorn's responsibility ensures that the cleanup will
be run even if the worker is suddenly shut down. This prevents the
worker from having to check for old repos at startup, allowing multiple
workers to coexist in the same pod.

Dockerfile

@@ -11,8 +11,9 @@ ARG PORT
 WORKDIR $APP_HOME
 COPY python/activator activator/
 COPY pipelines pipelines/
+COPY config/gunicorn.conf.py ./
 CMD source /opt/lsst/software/stack/loadLSST.bash \
     && setup lsst_distrib \
     && exec gunicorn --workers 1 --threads 1 --timeout $WORKER_TIMEOUT --max-requests $WORKER_RESTART_FREQ \
         --graceful-timeout $WORKER_GRACE_PERIOD \
-        --bind :$PORT 'activator.activator:create_app()'
+        --bind :$PORT --config gunicorn.conf.py 'activator.activator:create_app()'

config/gunicorn.conf.py

@@ -0,0 +1,5 @@
+from activator.activator import cleanup_worker
+
+
+def worker_exit(server, worker):
+    cleanup_worker()

python/activator/activator.py

@@ -19,7 +19,7 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-__all__ = ["check_for_snap", "next_visit_handler"]
+__all__ = ["check_for_snap", "next_visit_handler", "cleanup_worker"]
 
 import collections.abc
 import functools
@@ -151,10 +151,6 @@ def create_app():
         _get_storage_client()
         _get_central_butler()
 
-        for old_repo in find_local_repos(local_repos):
-            _log.warning("Orphaned repo found at %s, attempting to remove.", old_repo)
-            flush_local_repo(old_repo, _get_central_butler())
-
         app = Flask(__name__)
         app.add_url_rule("/next-visit", view_func=next_visit_handler, methods=["POST"])
         app.register_error_handler(500, server_error)
@@ -167,6 +163,17 @@ def create_app():
         sys.exit(3)
 
 
+def cleanup_worker():
+    try:
+        local_repo = _get_local_repo()
+        _log.info("Removing local repo at %s.", local_repo.name)
+        flush_local_repo(local_repo.name, _get_central_butler())
+        local_repo.cleanup()
+    except FileNotFoundError:
+        # If the repo doesn't exist, there's no problem.
+        pass
+
+
 def _graceful_shutdown(signum: int, stack_frame):
     """Signal handler for cases where the service should gracefully shut down.