PyMacaron

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A python microservice framework

Reference:

Overview
Get started
Write an API specification
Implement your API
Deploy to AWS
JWT authentication
Configuration
Error handling
Asynchronous execution
Database serialisation
Testing

Asynchronous Execution

pymacaron-async is a an extension of pymacaron that seamlessly adds asynchronous task execution based on celery/Redis to your API endpoints.

Install

Install redis in your dev environment:

apt-get install redis-server
pip install redis

Then install ‘pymacaron-async’:

pip install pymacaron-async

And add it to your microservice dependencies:

echo 'pymacaron-async' >> requirements.txt

Usage

Instruct the pymacaron server to start celery workers by adding the following line in ‘pym-config.yaml’:

with_async: true

And make python methods asynchronous by decorating them as follows:

from pymacaron_async import asynctask
from pymacaron_core.swagger.apipool import ApiPool

# Make send_email into an asynchronously
# executable method, called via celery, to
# be executed after the REST endpoint has
# returned.
@asynctask
def send_email(title):
    # Call 3-rd party emailing API pass
    pass

# API endpoint, defined in your swagger API spec
def do_signup_user():
    do_stuff()

    # Schedule a task sending this email
    # and go on, not waiting for the result
    send_email('Welcome !')

    return ApiPool.myapi.model.Ok()

That’s all.

Known issues

Arguments to the asynchronous methods should not be classes instances, since celery won’t serialize them correctly when passing them to the asynchronous task. Dicts, arrays and base types work fine.

Why and how?

It is considered good behavior for a REST api endpoint to return as quickly as possible. Any long running task it needs to perform, such as image manipulation, 3rd party calls whose replies are not immediately needed, logging or analytics, should be executed after returning the HTTP response to the api caller.

Unfortunately, this is not trivially done. Except with pymacaron-async :-)

pymacaron-async adds asynchronous execution capability to pymacaron servers, by spawning in the background a celery worker in which all your api modules are loaded. The celery worker loads your swagger api files in just the same way as the pymacaron server, imports all the modules containing your endpoint implementations and emulates a Flask context including the current user’s authentication details. That way, code executed asynchronously in a celery task sees exactly the same context as code executing synchronously in the endpoint method.