Google App Engine with Flask: Memorystore/redis produces [Errno 104] Connection reset by peer - google-app-engine

Question

My Flask-based GAE app has been running for a few weeks without issue. Today I noticed the root URL produces a 500 Internal Server Error most of the time. In the logging I see this appears to be related to session handling in Flask (using Flask-Session). Before transitioning to GAE, this app ran on a VM with local Redis instance for well over a year without any problems.
The Memorystore instance has only about 1500 keys at this time and 3 or 4 mb of data, so it is not heavily loaded. The server itself receives very little traffic (just me and the occasional robot). I am looking for insight as to what has produced this change in behavior or what diagnostic procedures I should pursue since I am new to GAE and the Google Cloud environment.
A typical traceback of the failure looks like this:
Traceback (most recent call last):
File "/env/lib/python3.7/site-packages/flask/app.py", line 1969, in finalize_request response = self.process_response(response)
File "/env/lib/python3.7/site-packages/flask/app.py", line 2268, in process_response self.session_interface.save_session(self, ctx.session, response)
File "/env/lib/python3.7/site-packages/flask_session/sessions.py", line 166, in save_session time=total_seconds(app.permanent_session_lifetime))
File "/env/lib/python3.7/site-packages/redis/client.py", line 1540, in setex return self.execute_command('SETEX', name, time, value)
File "/env/lib/python3.7/site-packages/redis/client.py", line 836, in execute_command conn = self.connection or pool.get_connection(command_name, **options)
File "/env/lib/python3.7/site-packages/redis/connection.py", line 1065, in get_connection if connection.can_read():
File "/env/lib/python3.7/site-packages/redis/connection.py", line 682, in can_read return self._parser.can_read(timeout)
File "/env/lib/python3.7/site-packages/redis/connection.py", line 295, in can_read return self._buffer and self._buffer.can_read(timeout)
File "/env/lib/python3.7/site-packages/redis/connection.py", line 205, in can_read raise_on_timeout=False)
File "/env/lib/python3.7/site-packages/redis/connection.py", line 173, in _read_from_socket data = recv(self._sock, socket_read_size)
File "/env/lib/python3.7/site-packages/redis/_compat.py", line 58, in recv return sock.recv(*args, **kwargs) ConnectionResetError: [Errno 104] Connection reset by peer
Again, this is new behavior. The server worked flawlessly for a couple of weeks. What might have changed and where should I look?
Possible related issue: https://github.com/andymccurdy/redis-py/issues/1186

Answer 1

Using health_check_interval eliminated most, but not all of these "Connection reset by peer" errors for us (GAE Python 2.7):
self._redis = Redis(
environ.get("REDISHOST", "localhost"),
int(environ.get("REDISPORT", 6379)),
health_check_interval=30,
)
Perhaps a value lower than 30 would eliminate the remaining occurrences.