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Empowering Django with Background Workers text-center shiki slide-left true false
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Empowering Django with Background Workers

Jake Howard

  • Senior Systems Engineer @ Torchbox
  • Security & Performance @ Wagtail
  • theorangeone.net
  • @RealOrangeOne
  • @RealOrangeOne
  • @jake@theorangeone.net

layout: center

Django isn't just for websites

flowchart LR
    U(User 🧑‍💻)
    D[\Django/]

    U---->|Request|D
    D---->|Response|U

layout: full

flowchart BT
    U[User 🧑‍💻]
    D[\Django/]
    DB[(Database)]
    C[(Cache)]
    E>Email]
    EA[External API]
    V[[Video Transcode]]
    ML((Machine Learning))

    U---->|Request|D
    D---->|Response|U

    D-.-DB & E & EA & V & ML & C

layout: full

flowchart BT
    U[User 🧑‍💻]
    D[\Django/]
    DB[(Database)]
    C[(Cache)]
    E>Email]
    EA[External API]
    V[[Video Transcode]]
    ML((Machine Learning))
    B{{Background Processing}}

    U--->|Request|D
    D--->|Response|U

    D---B

    D-.-C & DB

    B---E & V & ML & EA
    B---C & DB

layout: cover

Background Workers?

layout: fact

flowchart LR
    D[\Django/]
    S[(Queue Store)]
    R1{Runner}
    R2{Runner}
    R3{Runner}

    D<--->S<-..->R1 & R2 & R3

layout: cover

When?

layout: fact

flowchart BT
    D[\Django/]

    subgraph Fast & Reliable
      DB[(Database)]
      C[(Cache)]
    end

    subgraph Slow / Unreliable
      E>Email]
      EA[External API]
      V[[Video Transcode]]
      ML((Machine Learning))
    end

    D---DB & C

    D-.-E & EA & V & ML

layout: cover

Background Workers in Django

layout: cover background: https://docs.celeryq.dev/en/stable/_static/celery_512.png

Celery!

layout: image-right image: https://images.unsplash.com/photo-1444703686981-a3abbc4d4fe3?q=80&w=1740&auto=format&fit=crop&ixlib=rb-4.0.3&ixid=M3wxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8fA%3D%3D

Others...

  • Celery
  • arq
  • Django DB Queue
  • Django Lightweight Queue
  • Django Too Simple Q
  • Django-Q
  • Django-Q2
  • Dramatiq
  • Huey
  • RQ
  • Taskiq
  • ...

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Email

layout: center

from django.contrib.auth.models import User
from django.core.mail import send_mail
from django.template.loader import render_to_string

import django_rq

from wagtail.models import Page

def send_email_to_user(page: Page, user: User):
    email_content = render_to_string("notification-email.html", {"user": user, "page": page})
    send_mail(
      subject="A page has been published",
      message=email_content
      from_email=None,  # Use the default sender email
      recipient_list=[user.email]
    )

for user in page.subscribers.iterator():
    django_rq.enqueue(send_email_to_user, user)

layout: center

A problem

```python
from django.contrib.auth.models import User
from django.core.mail import send_mail
from django.template.loader import render_to_string

import django_rq

from wagtail.models import Page

def send_email_to_user(page: Page, user: User):
    email_content = render_to_string("notification-email.html", {"user": user, "page": page})
    send_mail(
      subject="A page has been published",
      message=email_content
      from_email=None,  # Use the default sender email
      recipient_list=[user.email]
    )

for user in page.subscribers.iterator():
    django_rq.enqueue(send_email_to_user, user)
```

```python {all|7-9,20|all}
from django.contrib.auth.models import User
from django.core.mail import send_mail
from django.template.loader import render_to_string

from wagtail.models import Page

from my_celery_config import app

@app.task
def send_email_to_user(page: Page, user: User):
    email_content = render_to_string("notification-email.html", {"user": user, "page": page})
    send_mail(
      subject="A page has been published",
      message=email_content
      from_email=None,  # Use the default sender email
      recipient_list=[user.email]
    )

for user in page.subscribers.iterator():
    send_email_to_user.delay(user)
```

layout: image image: /situation.png backgroundSize: 50%

layout: image image: /ridiculous.png backgroundSize: 49%

layout: fact

Introducing*:

django.tasks

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  • API contract between library and application developers
  • Swappable backends through settings.py
  • Built in backends:
    • ORM
    • "Immediate"
    • "Dummy"
  • Django 5.2 🤞
    • Backport for 4.2+

layout: center

```python
from django.contrib.auth.models import User
from django.core.mail import send_mail
from django.template.loader import render_to_string

from wagtail.models import Page

from my_celery_config import app

@app.task
def send_email_to_user(page: Page, user: User):
    email_content = render_to_string("notification-email.html", {"user": user, "page": page})
    send_mail(
      subject="A page has been published",
      message=email_content
      from_email=None,  # Use the default sender email
      recipient_list=[user.email]
    )

for user in page.subscribers.iterator():
    send_email_to_user.delay(user)
```

```python {all|7-9,20|all}
from django.contrib.auth.models import User
from django.core.mail import send_mail
from django.template.loader import render_to_string

from wagtail.models import Page

from django.tasks import task

@task()
def send_email_to_user(page: Page, user: User):
    email_content = render_to_string("notification-email.html", {"user": user, "page": page})
    send_mail(
      subject="A page has been published",
      message=email_content
      from_email=None,  # Use the default sender email
      recipient_list=[user.email]
    )

for user in page.subscribers.iterator():
    send_email_to_user.enqueue(user)
```

layout: center

from django.contrib.auth.models import User
from django.core.mail import send_mail
from django.template.loader import render_to_string

email_content = render_to_string("email-template.html", {"page": page})

for user in page.subscribers.iterator():
    send_mail(
      subject="The page has changed",
      message=email_content
      from_email=None,  # Use the default sender email
      recipient_list=[user.email]
    )

# settings.py
EMAIL_BACKEND = "django.core.mail.backends.tasks.SMTPEmailBackend"

layout: image-right image: /soon.png class: flex justify-center text-2xl flex-col

Q: Why something new?

A: It doesn't have to be

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Q: Why something built-in?

  • Improve interoperability
  • Reduce cognitive load
  • Reduce barrier to entry

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{.max-h-48.mx-auto}

vs

{.max-h-32.mx-auto}

layout: center

{.max-h-48.mx-auto}

vs

{.max-h-32.mx-auto}

layout: section

Where are we now?

pip install django-tasks

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Where will we be soon™?

layout: cover background: https://docs.celeryq.dev/en/stable/_static/celery_512.png

Is this the end?

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Out of scope

  • Completion / failed hooks
  • Bulk queueing
  • Automated task retrying
  • Task runner API
  • Unified observability
  • Cron-based scheduling
  • Task timeouts
  • Swappable argument serialization

layout: cover background: https://images.unsplash.com/photo-1519187903022-c0055ec4036a?q=80&w=1335&auto=format&fit=crop&ixlib=rb-4.0.3&ixid=M3wxMjA3fDB8MHxwaG90by1wYWdlfHx8fGVufDB8fHx8fA%3D%3D

The future is bright

layout: section

What's next?

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QUESTIONS?