Maximum number of client connections in Flask-SocketIO with Eventlet

| Comments

It’s not mentioned in the docs for Flask-SocketIO that Eventlet has an option max_size which by default limits the maximum number of client connections opened at any time to 1024. There is no way to pass it through flask run command, so the application should be run with socketio.run, for example:

...
if __name__ == '__main__':
    socketio.run(app, host='0.0.0.0', port='8080', max_size=int(os.environ.get('EVENTLET_MAX_SIZE', 1024)))

How to split Celery tasks file

| Comments

Suppose there is a large tasks.py file, like this:

@celery.task()
def task1():
    ...

@celery.task()
def task2():
    ...
    task1.delay()
    ...

...

A good idea is to split it on the smaller files, but Celery auto_discover by default search tasks in package.tasks module, so one way to do this is to create a package tasks and import tasks from other files in __init__.py.

__init__.py

from .task1 import task1
from .task2 import task2

__all__ = ['task1', 'task2']

task1.py

@celery.task()
def task1():
    ...

task2.py

from .task1 import task1

@celery.task()
def task2():
    ...
    task1.delay()
    ...

CSRF exempt for Flask-RESTPlus API

| Comments

The @csrf.exempt method does not work with Resource methods or decorators, it should be done on Api level. Here is an example how to exclude resources from CSRF protection based on class:

def csrf_exempt_my_resource(view):
    if issubclass(view.view_class, MyResource):
        return csrf.exempt(view)
    return view

api_blueprint = Blueprint('api', __name__)
api = Api(api_blueprint, title='My API', decorators=[csrf_exempt_my_resource])

Or for all resources:

api_blueprint = Blueprint('api', __name__)
api = Api(api_blueprint, title='My Private API', decorators=[csrf.exempt])

Function as model column in Flask Admin

| Comments

I like the idea about separation of business logic from models and views into services. There are more details in these slides from the EuroPython talk.

Usually in Flask-Admin for a new column a new method with @property decorator is added and the model becomes fat. Also it’s not good to put something with queries in property. Another way is to put this function to the services and use column formatter in Flask-Admin.

def get_some_data(model_id)
    """Function in services."""
    return RelatedModel.objects(model=model_id).count()

class MyModelView(ModelView):
    column_formatters = {
        'related_model_count': lambda view, context, model, name: get_some_data(model.id)
    }    

    column_list = [..., 'related_model_count']

Docker healthcheck for Flask app with Celery

| Comments

With docker-compose it can be done the next way

flask_app:
    ...
    healthcheck:
      test: wget --spider --quiet http://localhost:8080/-/health
celery_worker:
    ...
    command: celery worker --app app.celeryapp -n worker@%h --loglevel INFO
    healthcheck:
      test: celery inspect ping --app app.celeryapp -d worker@$$HOSTNAME

Where /-/health is just a simple route

@app.route("/-/health")
def health():
    return 'ok'

How to update docker service using a version from docker-compose

| Comments

Here is a small script which compares the version of the running service and the version in the docker-compose file, if they are different it runs an update.

REDIS_VERSION=$(docker service ls | grep "redis" | awk '{print $5}')
REDIS_NEW_VERSION=$(grep -Po "image:\s*\Kredis:.*" docker-compose.yml)
if [ "$REDIS_VERSION" != "$REDIS_NEW_VERSION" ]; then
    echo "update $REDIS_VERSION -> $REDIS_NEW_VERSION"
    docker service update --image $REDIS_NEW_VERSION app_redis
fi

Env variables for Vue.js in Nginx container

| Comments

The default approach for Vue.js is to use .env files during build stage. But I like more this one with envsubst. There is no need to rebuild image for each environment or when the configuration is changed.

Here is a small modification for entrypoint.sh, so it can replace all variables with VUE_APP_ prefix.

#!/bin/sh

function join_by { local IFS="$1"; shift; echo "$*"; }

# Find vue env vars
vars=$(env | grep VUE_APP_ | awk -F = '{print "$"$1}')
vars=$(join_by ' ' $vars)
echo "Found variables $vars"

for file in /dist/js/app.*;
do
  echo "Processing $file ...";

  # Use the existing JS file as template
  cp $file $file.tmpl
  envsubst "$vars" < $file.tmpl > $file
  rm $file.tmpl
done

exec "$@"
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