Microservices
with Django

Florian Demmer - www.floriandemmer.com

... examples and thoughts

Django Friends Meetup, 2015-08-06

What? Why?

motivation

• separation of concerns
• from code reuse to service reuse
• scaling: performance by adding instances
• high availability?
• security?

microservices

• nothing new, actually: unix philosophy
• evolution: library vs. service
• service components
  • independently deployed services
  • communicating over high level API

kind of like Software as a Service

a don't-example

We want a centralized accounts service!

MongoDB + Flask = REST API

• API provides JSON of accounts model
• CRUD is not enough:
  • /account/<id>/add_device
  • /account/<id>/verify_email
• performance: single SQL query was replaced by multiple HTTP requests

a do-example

We want to send a newsletter!

let's buy <some SoA>
use it with Celery tasks and requests

• setup via Web UI
• send mail as JSON via HTTP/REST
• CRUD is enough
• performance:
  no problem is done async

it depends...

does the problem really fit the solution?

• sending email is already async by design
• using an account to log in is not

so... security?

We want to keep the Internet out of our office CRM/CMS/...!

• Web UI for external users with access to limited dataset
• Web UI for internal office use with access to full sensitive data

the plan

2x Django + Celery (Redis)

• RPC characteristics
• Celery (async/sync, retry, worker queues)
• Redis ("good enough", multiple queues, JSON or pickle ...)

the code

# frontend service: webservice.py
@shared_task
def update_or_create_user(username, password):
    ...


# backend service: tasks.py
from celery import signature

update_or_create_user = signature('webservice.update_or_create_user')


# backend service: signals.py
from tasks import update_or_create_user

ref_id = update_or_create_user(username, make_password(password))

the horror!

• multiple git repositories
• sharing common code is hard
• keep communication endpoints clean
• multiple IDEs/vagrant boxes at once
• timeouts and failure

What do you think?

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