Google App Engine dev_appserver.py + Cloud Datastore Emulator: crash on startup without log warnings or errors (exit status 245)

Question

I'm trying to run the Google App Engine local development server (dev_appserver.py) together with the Cloud Datastore Emulator.

Environment:

• Ubuntu 22.04.1 LTS on WSL (Windows 11 Pro 22621.1265)
• /usr/bin/python2 --version: 2.7.18
• ./venv/bin/python2 --version: 2.7.18
• /usr/bin/python3 --version: 3.10.6
• /usr/bin/gcloud --version:

Google Cloud SDK 418.0.0
alpha 2023.02.13
app-engine-python 1.9.101
beta 2023.02.13
bq 2.0.85
bundled-python3-unix 3.9.16
cloud-datastore-emulator 2.3.0
core 2023.02.13
gcloud-crc32c 1.0.0
gsutil 5.20

• /usr/bin/java --version:

openjdk 11.0.17 2022-10-18
OpenJDK Runtime Environment (build 11.0.17+8-post-Ubuntu-1ubuntu222.04)
OpenJDK 64-Bit Server VM (build 11.0.17+8-post-Ubuntu-1ubuntu222.04, mixed mode, sharing)

Background: I'm migrating an existing Python 2 server to Python 3.

Minimal scenario to reproduce the problem:

gae.sh:

#! /usr/bin/env bash

export DATASTORE_DATASET=myproject
export DATASTORE_EMULATOR_HOST=localhost:8087
export DATASTORE_EMULATOR_HOST_PATH=localhost:8087/datastore
export DATASTORE_HOST=http://localhost:8087
export DATASTORE_PROJECT_ID=myproject

python2 \
    /usr/bin/dev_appserver.py \
    --runtime_python_path=/usr/bin/python3 \
    --application=myproject \
    --host=localhost \
    --port=8082 \
    --support_datastore_emulator=true \
    --require_indexes=true \
    --running_datastore_emulator_host=localhost:8087 \
    --datastore_emulator_port=8087 \
    --log_level=debug \
    --dev_appserver_log_level=debug \
    ./app.yaml

datastore.sh:

#! /usr/bin/env bash

gcloud beta emulators datastore start \
    --project=myproject \
    --host-port=localhost:8087 \
    --verbosity=debug

app.yaml:

# Same result with python35 python36 python37 python38 python39 python310 python311
runtime: python310
# Any other options are not changing the outcome
# app_engine_apis: true
# service: default
# entrypoint: python3 -m main

requirements.txt:

# The emulator never reaches the point to install dependencies
# appengine-python-standard>=1.0.0
# Flask==1.1.4
# MarkupSafe==2.0.1

main.py:

# The WSGI application is not run at all (regardless of the app.yaml options)
from flask import Flask

app = Flask(__name__)

@app.route('/')
def home():
    return 'Hello, World!'

if __name__ == "__main__":
    app.run(host='localhost', port=8083, debug=True)

Set up and activate the virtual environment:

virtualenv -p /usr/bin/python2 ./venv
source ./venv/bin/activate

grpcio is required by the emulator (https://cloud.google.com/appengine/docs/legacy/standard/python/tools/migrate-cloud-datastore-emulator):

pip2 install grpcio

To attempt starting the emulator, simply run:

./gae.sh

Which outputs:

WARNING:  Python 2 will soon be deprecated by the Google Cloud SDK
and may not function correctly. Please use Python version 3.5 and up.

If you have a compatible Python interpreter installed, you can use it by setting
the CLOUDSDK_PYTHON environment variable to point to it.

WARNING:  Python 2 will soon be deprecated by the Google Cloud SDK
and may not function correctly. Please use Python version 3.5 and up.

If you have a compatible Python interpreter installed, you can use it by setting
the CLOUDSDK_PYTHON environment variable to point to it.

INFO     2023-02-24 11:20:19,042 devappserver2.py:240] Using Cloud Datastore Emulator.
We are gradually rolling out the emulator as the default datastore implementation of dev_appserver.
If broken, you can temporarily disable it by --support_datastore_emulator=False
Read the documentation: https://cloud.google.com/appengine/docs/standard/python/tools/migrate-cloud-datastore-emulator
Help us validate that the feature is ready by taking this survey: <**edited out because not allowed on Stack Overflow**>
Report issues at: https://issuetracker.google.com/issues/new?component=187272

INFO     2023-02-24 11:20:19,056 devappserver2.py:317] Skipping SDK update check.
WARNING  2023-02-24 11:20:19,428 <string>:711] Detected environment variable DATASTORE_EMULATOR_HOST=localhost:8087, dev_appserver will speak to the Cloud Datastore emulator running on this address. The datastore_path /tmp/appengine.myproject.myname/datastore.db will be neglected.
If you want datastore to store on /tmp/appengine.myproject.myname/datastore.db, remove DATASTORE_EMULATOR_HOST from environment variables and restart dev_appserver
INFO     2023-02-24 11:20:19,610 <string>:384] Starting API server at: http://localhost:38867

At that point the process ends.

The only output warnings are the deprecation of Python 2 (but that's still required according to https://cloud.google.com/appengine/docs/standard/tools/local-devserver-command?tab=python) and the one regarding DATASTORE_EMULATOR_HOST.

If I run echo $? (get the exit code) I get 245.

dev_appserver.py will crash regardless of whether the Datastore emulator was started with:

./datastore.sh

Turning the Datastore Emulator off by simply setting --support_datastore_emulator=false in gae.sh starts the application perfectly well, but of course without Datastore emulation, so all related functionality will fail at runtime.

Answer 1

Start the datastore emulator. After the emulator is running, open a new shell and then run dev_appserver.py in the new shell.

My experience with datastore emulator is that you need to open a new shell after starting the emulator/setting the environment variables for the its environment variables to apply.