---
title: Bringing Background Workers to Django
class: text-center
highlighter: shiki
transition: slide-left
mdc: true
monaco: false
themeConfig:
  primary: '#0c4b33'
---

# Bringing Background Workers to <logos-django class="[&>path]:fill-white! h-15 w-43"/>

## Jake Howard{.mt-5}

### Django London{.mt-5}
#### September 2024

<!--
- Here to talk about Background Workers
  - What they are
  - How to use them
  - Exciting things _hopefully_ coming to Django
-->
---
layout: full
---

# `$ whoami`

<ul class="list-none! [&>li]:m-0! text-2xl mt-10">
  <li><mdi-fire class="fill-white"/> Senior Systems Engineer @ Torchbox</li>
  <li><logos-wagtail class="fill-white"/> Core, Security & Performance teams @ Wagtail</li>
  <li><logos-django-icon class="[&>rect]:hidden!" /> Django Software Foundation Member</li>
  <li><mdi-server-plus class="fill-white" /> I'm an avid self-hoster</li>
  <li><mdi-robot-excited class="fill-white" /> I help students build robots in my "spare" time <small>(https://srobo.org)</small></li>
</ul>

<ul class="list-none! text-sm [&>li]:m-0! mt-10 text-xl">
  <li><mdi-earth /> theorangeone.net</li>
  <li><mdi-github /> @RealOrangeOne</li>
  <li><mdi-twitter /> @RealOrangeOne</li>
  <li><mdi-mastodon /> @jake@theorangeone.net</li>
</ul>

<div class="absolute right-3 top-3">
  <img src="/dls24-qrcode.png" width="190px" />
</div>

<!--
- Hi
- I'm Jake
- Senior Systems Engineer at Torchbox
- I'm also on the security team, core team and performance teams for Wagtail
  - Leading Django-based CMS
- Since doing this talk at Djangocon, I'm also a DSF member
- I exist in many places on the internet
-->

<style>
    .slidev-layout {
        background-color: #e85537;
    }
</style>

---
layout: center
---

# Django is a web framework

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

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

<style>
  .mermaid {
    text-align: center;
  }
</style>

<!--
- Django is a web framework
- It's a magic box which turns HTTP requests into HTTP responses
    - What you do inside that box is up to you
- For something like a blog, that's probably as far as it needs to go
-->

---
layout: full
---

# Django isn't _just_ for websites

```mermaid
flowchart BT
    U[User 🧑‍💻]
    D[\Django/]
    DB[(Database)]
    E>Email]
    EA[External API]
    V[[Video Transcoding]]
    R[Reporting]
    ML((Machine<br>Learning))

    U<--->D

    D---DB
    D-..-E & EA & V & R & ML
```

<style>
  .mermaid {
    text-align: center;
  }
</style>

<!--
- For a full web application, you need a little more than that
    - Not just "keep information in a database"
    - Notification emails
    - Talk to external services
    - Transcoding video
    - Complex reporting
    - It's 2024, so lots of ML
- For many of these, you need code which runs outside the magic box
    - You don't want your user waiting whilst these happen
        - If you had to wait whilst YouTube transcoded all your videos, you'd get pretty annoyed
-->

---
layout: full
---

<v-click>

# Background Workers?

</v-click>

```mermaid
flowchart BT
    U[User 🧑‍💻]
    D[\Django/]

    E>Email]
    EA[External API]
    V[[Video Transcoding]]
    R[Reporting]
    ML((Machine<br>Learning))

    B{{<strong>Background Worker</strong>}}

    U<-->D

    D-..-B

    B---E & EA & V & R & ML
```

<style>
  .mermaid {
    text-align: center;
  }
</style>

<!--
- You need a background worker
    - But[click]
    - What _are_ background workers
- Let you offload complexity outside of the request-response cycle
    - To be run somewhere else, potentially at a later date

- They keep requests nice and fast
    - Move the slow bits somewhere else
        - User doesn't have to wait
    - Improves throughput and latency
-->

---
layout: section
---

## Background worker architecture

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

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

<!--
- How does this work?
    - Web process submits a function to be run
    - Stored in the queue store
    - A runner then grabs a task, runs it, and returns the result to the queue store
    - You can retrieve its status later if needed
-->

---
layout: section
---

# When?

<!--
- Background workers are very useful tool
    - But that doesn't mean they're useful for everything, all the time

- As with all great things: "It depends" when they're useful
    - Trade-off between complexity and functionality
- If you're considering whether an action makes sense in the background:
    - There are a few things to consider...
-->

---
layout: cover
background: https://images.unsplash.com/photo-1518729371765-043e54eb5674?q=80&w=1807&auto=format&fit=crop&ixlib=rb-4.0.3
---

# Does it take time?{.text-right}

<!--
- Does it take time
    - Or _could_ it take time
- Don't want to make the user wait
    - Unable to close the tab or do something else
- Go off and do it in the background, and let them know whether it's done
    - Even if that's by polling it in the browser
-->

---
layout: fact
---

## Does it leave your infrastructure?{.mb-5}

```mermaid
flowchart BT
    D[\Django/]

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

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

    D---DB & C

    D-.-E & EA & V & R & ML
```

<!--
- Does control leave your infrastructure?
- The core components (Server, DB, Cache etc) you control and can closely monitor
    - And are in a good position to fix it if something goes wrong
- That's not true for external APIs
    - It's someone else's SRE team
- Their performance characteristics shouldn't affect your app
-->

---
layout: cover
background: https://images.unsplash.com/photo-1518770660439-4636190af475?q=80&w=3870&auto=format&fit=crop&ixlib=rb-4.0.3
---

# Specialized hardware?

<!--
- Maybe it's less about when, more about where?
- Maybe it's more about the hardware it runs on
    - GPUs
    - Loads of RAM
    - External hardware
    - Isolated network
-->

---
layout: image-right
image: https://images.unsplash.com/photo-1711606815631-38d32cdaec3e?q=80&w=2070&auto=format&fit=crop&ixlib=rb-4.0.3
class: text-xl
---

# Examples

- Compiling code
- Complex reporting
- File uploads
- Model training
- PDF generation
- Resizing images
- Sending email
- Transcoding video
- ... 🤯

<!--
- Background workers have a world of uses
- It's important to consider the scale when designing a feature
  - It might be fine locally
  - As your application grows, there'll be more data, so it'll likely take a lot longer
- The user shouldn't have to wait ages for your application
    - They can get back on with their day
    - Web servers can get back to processing other requests
- This list is quite long
    - And it's nowhere near complete
    - It's a very generic tool
- When designing an app at scale with these features
    - Maybe consider moving it to the background.
-->

---
layout: section
---

# Background Workers in

<logos-django class="[&>path]:fill-white! h-fit w-60 -mt-20"/>

<!--
- Back to Django
    - This is Django London after all
- In Python and Django, there are lots of different frameworks to achieve background workers
-->

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

# Libraries

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

<!--
- All require an external library
    - And possibly some external infrastructure
- Celery is probably the biggest one
    - But it's not all that exists
- So many different libraries exist
    - With different strengths / weaknesses
    - Different learning curves (or cliffs)
-->

---
layout: cover
background: https://images.unsplash.com/photo-1522096823084-2d1aa8411c13?q=80&w=1740&auto=format&fit=crop&ixlib=rb-4.0.3
---

## Example:
# Email <mdi-email-fast-outline />

<!--
- Let's loon at an example, sending an email
    - Very common functionality
- Let's imagine a CMS
    - For totally unbias reasons
- When a page is published, send an email to everyone subscribed
-->

---
layout: center
---

# Sending an email

```python {all|7|8|9-14|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

for user in page.subscribers.iterator():
    email_content = render_to_string("notification-email.html", {"user": user, "page": page})
    send_mail(
      subject=f"A change to {page.title} has been published",
      message=email_content
      from_email=None,  # Use the default sender email
      recipient_list=[user.email]
    )
```

<!--
- Here's the code we might write to do that

1. [click]Find the users to email
2. [click]Construct the email content
3. [click]Send the email

- [click]This works perfectly fine
    - Scales _relatively_ well
- But has some issues
    - If connecting to the email server takes a while, the user has to wait
        - Usually only a few ms
        - Might take a few seconds
    - If something goes wrong with one email, the others won't send
        - What if your email gateway is down altogether - do your requests start erroring?
            - How do you handle it if they do?
- That web worker (eg gunicorn) can't process any other requests until this is done
-->

---
layout: center
---

```python {all|18|19|10|11-16|all|18-19|all}
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=f"A change to {page.title} 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)
```

<!--
- Let's look at an example of how we might use background workers to help with this
    - Use Django-RQ for this

1. [click]Find the users to email
2. [click]New: Start a task for each user
3. [click]Construct the email content
4. [click]Send the email

- [click]Most of this is exactly the same
    - If you knew nothing of RQ, you could still maintain this code

- [click]Moving it to the background just quickly puts an item in the queue
    - And then the user can get back on with their life
    - Emails get sent out by the runners
        - Multiple runners means they get sent out faster

- [click]Email sending is an easy action to move to the background
    - It's a connection to an external API
        - Variable latency
        - Infrastructure you don't control
    - All of that is simpler to handle when it's already running in the background
-->

---
layout: center
---

# Using <span v-click.hide="1">RQ</span><span v-click="1"><s class="opacity-60">RQ</s> Celery</span>

````md magic-move
```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=f"A change to {page.title} 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=f"A change to {page.title} 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)
```
````

<style>
  .slidev-vclick-hidden {
    display: none;
  }
</style>

<!--
- There's something I just said which might end up causing issues
    - You'll notice I said "Using RQ" in that example
- That's because each worker library has its own API
    - Its own features
    - Its own configuration
    - Its own caveats / implementation details
- What if we wanted to use Celery instead?
    - [click]Well, that's easy
    - [click]Just change a few lines
- [click]But there in lies the problem
    - You had to make some changes!
    - Sure, they're small, but this is only a tiny amount of code
    - What if you wanted to support both?
-->
---
layout: image
image: /situation.png
backgroundSize: 50%
---

<!--
- It's hard enough having multiple options
    - But how do you choose between them?
        - Maybe you have experience with libraries already
        - Do you have the time (and patience) to test each one out?
        - Maybe you already have a standard you need to work to
        - Maybe you need specific features
    - If you're new to Django, do you really want to spend the time weighing them all up?
        - Knowing it could bite you as you grow or need a specific feature
        - Requiring a lot of time refactoring in future

- What about library maintainers
    - Like, say, Wagtail
    - Do you write and maintain integrations for _all_ task libraries
    - Do you choose the big one(s) and force your users' hands?
    - Do you expose a hook and let your users integrate themselves?

- It adds a huge maintenance burden, whichever you choose
    - There isn't really a right answer
-->

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

<!--
- There _should_ be one universal standard which combines them all
- A single API to help developers use a library
    - Without tieing their hands
- First-party
    - Allowing library developers to depend on it
    - Instead of supporting every separate API
- Scale easily as your needs change
    - Be easy to get started with for small projects
    - But feature-packed for larger deployments
- Allowing easy stubbing out during tests
    - Tests are important!
-->

---
layout: fact
---

## Introducing*:{.mb-5 .mt-3}

# `django.tasks`

<div class="absolute right-1/2 translate-x-1/2 top-3">
  <img src="/django-tasks-qrcode.png" width="150px" />
</div>

<!--
- In progress API spec for first-party background workers in Django
- An approved Enhancement Proposal, slowly making its way into Django itself
-->

---
layout: image-right
image: https://images.unsplash.com/photo-1674027444485-cec3da58eef4?q=80&w=1932&auto=format&fit=crop&ixlib=rb-4.0.3
class: flex items-center text-xl
---

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

<!--
- An API contract between worker library maintainers and application developers
    - Compatibility layer between Django and their native APIs
    - Hopefully the promise of "Write once, run anywhere"
- Built-in implementations
    - ORM based (production grade, building on the power of the ORM)
    - "Immediate" (ie doesn't background anything) loaded by default
    - Dummy (for testing)
- Hopefully landing in Django 5.2
    - Backwards compatible with Django 4.2, to allow easy adoption
-->

---
layout: center
---

# <span v-click.hide="1">Using Celery</span><span v-click="1">Using <code>django.tasks</code></span>

````md magic-move
```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=f"A change to {page.title} 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
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_id: int, user_id: int):
    page = Page.objects.get(id=page_id)
    user = User.objects.get(id=user_id)
    email_content = render_to_string("notification-email.html", {"user": user, "page": page})
    send_mail(
      subject=f"A change to {page.title} 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.id)
```
````

<style>
  .slidev-vclick-hidden {
    display: none;
  }
</style>

<!--
- Let's look at the same code example as before
- This is tied to Celery
    - If want to support RQ too, I'd have to duplicate some parts
- Instead, let's write this once to use `django.tasks`[click]
    - Still simple, clear, approachable and easy to use
        - If I say so myself
- If we swapped to RQ: 0 lines need to change
    - If a new library comes out, 0 lines need to change
- If this is in a library, not my own code, I'm not constrained by their preferences
    - And the maintainer doesn't have extra work to support my preferences
      - They can use what they like, I can use what I like
- For testing, I can use an in-memory backend
    - With 0 lines changed
-->

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

# Q: Why something new?

<!--
- I'm sure you're thinking "Why something new?"
    - Celery already has a borderline monopoly on task queues
    - Writing a production-grade task queue is hard
        - As I've been told whilst working on this DEP
    - Why not just vendor something existing?
        - If not Celery, then something else
- That's not really the goal
    - Shared API contract is
        - Interoperate with as opposed to replace
        - Let you use the ecosystem which already exists
    - The Django backends will hopefully become great
        - But must be done with careful planning and consideration
        - Django needs to remain the stable and reliable base it always has been
        - Don't want to burn-out the Django maintainers
-->

---
layout: image-right
image: https://images.unsplash.com/photo-1525683879097-8babce1c602a?q=80&w=1335&auto=format&fit=crop&ixlib=rb-4.0.3
class: flex justify-center text-xl flex-col
---

# Q: Why something built-in?

- Reduce barrier to entry
- Reduce cognitive load
- Reduce complexity for smaller projects
- Improve interoperability
- Use what's already there
- A common API

<!--
- Why should this be built-in?
- Being built-in reduces the barrier to entry
- Integrating becomes much simpler
    - There's 1 API to learn
        - It will last you a while
            - Scale with your needs
    - A developer can join a new project and already be productive
- A common API also helps library maintainers
    - Maintaining a library is work enough
        - Without needing to think about how to move code to the background
    - If Django can take complexity off you, great
        - Use the tools provided to you
    - Currently, it's not really an option
        - The burden is too great
    - No additional dependencies for your library
        - Just import from Django and you're set
        - The user can use what they want
            - Or what's suitable for their scale and use case
    - Now the barrier is reduced, the ecosystem can flourish
        - Libraries can assume background workers, without any additional burden
- The ORM backend should work for the majority of projects
    - If you just want to send emails in the background, you probably don't need Celery or RQ
        - It's overkill
    - A vendored solution makes it the easiest to get started with
        - Tweak some settings, run an extra process, and you're done.
-->

---
layout: center
transition: fade
---

![](/celery.svg){.h-32.mx-auto}

## vs

![](/postgres.png){.h-36.mx-auto}


<style>
.slidev-layout {
    background: white;
    color: black;
    text-align: center;
}
</style>

<!--
- ORM at scale
    - For some scales, an ORM-based worker might not be viable
        - The Sentrys and Instagrams of the world
        - Postgres scales pretty well, but sometimes not well enough
            - And that's ok!
-->

---
layout: center
---

![](/elasticsearch.png){.h-32.mx-auto}

## vs

![](/postgres.png){.max-h-36.mx-auto}


<style>
.slidev-layout {
    background: white;
    color: black;
    text-align: center;
}
</style>

<!--
- But the same is also true for Postgres FTS vs ElasticSearch
    - A debate that's been going on for a while
    - And I've had many times
- ElasticSearch is quite likely better for the ~10% of people who need it
- But that doesn't mean the other 90% of people won't be happy with PostgreSQL
    - Probably wouldn't benefit from ElasticSearch anyway
    - Definitely won't get a return on the extra hosting cost and complexity
- They'll be perfectly happy with Postgres FTS
    - Let them get started the easiest way possible
    - We can still invite them into ElasticSearch when they're ready
-->

---
layout: section
---

# Where are we now?

<!--
- I mean, other than Kraken HQ
-->

---
layout: image
image: /dep.png
---

<!--
- There's an approved DEP
- "In theory", it can go into Django
- Depending on what "it" is
-->

---
layout: image
image: /pypi.png
---

<!--
- You can use it right now
    - Please do, it's great!
    - For some projects, you won't need anything else
- Supporting all versions of Django and Python
    - No excuse to give it a go
- Report back the bugs
    - The more testing done now, the better
- There's still work to do
    - Features
    - Improvements
    - Performance
    - Scalability
    - The list goes on...
-->

---
layout: section
---

# Where will we be _soon_™?

<!--
- More testing
- More features
    - Writing task queues takes time
- Upstreaming
    - That's the big benefit
        - Else it really is just another standard
    - Once `django-tasks` is in a better state, it can become `django.tasks`
        - Hopefully in time for the 5.2 release window
- Adoption
    - The more people know about this, the better it is for everyone
    - Developers can start working on integrating now
        - Knowing they can trivially upgrade once it's in Django
- Integration
    - Can't use other libraries until the integrations exists
-->

---
layout: cover
background: /celery.svg
---

# Is this the end?

<style>
.slidev-layout {
    background: white;
    background-size: contain !important;
}
</style>

<!--
- Is this the end for Celery and alike?
    - Not at all!
    - It's a great choice
    - They have quite a head start
    - This is much more about usability and flexibility
    - If you need certain features, keep using them!
- Now you have the option of a Django-native API
    - Which could even be Celery under the hood
-->

---
layout: image-right
image: https://images.unsplash.com/photo-1451187580459-43490279c0fa?q=80&w=1744&auto=format&fit=crop&ixlib=rb-4.0.3
class: flex justify-center flex-col text-xl
---

# Out of scope (_for now_)

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

<!--
- The world of background workers is huge
    - There are countless nice features
    - Not everything is making it into the initial version(s)
        - And that's ok!
- Existing libraries have a head start
    - But I hope we can slowly catch them up
    - Bringing the stability and longevity guarantees that come with Django
    - Doesn't mean they'll never come
- With your help, we can make these happen
    - Except swappable argument serialization
        - `pickle` is a bad idea
-->

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

# The future is bright

<!--
- The future is bright though
- In time, I see more and more people reaching to `django.tasks`
- And background workers in general
    - Moving work to the background will make Django apps _seem_ faster
        - Improve throughput
        - Reduce latency
        - Improve reliability
- Gone are the days of needing additional research and testing to find the tooling you need
    - You can use the ones built-in to Django
    - And as you scale, it's easy to change
        - _without_ rewriting half your application
        - With all the knowledge to make an informed decision
    - A lower barrier helps everyone!
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# What's next?

## `pip install django-tasks`

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- Time to turn the dream into a reality!

- If you've realised you could use a background queue, give `django_tasks` a try
    - Test it out
    - Report back your issues
    - Suggest improvements
    - Issues / Discussions are open and active
- If you want to get involved, please do!
    - There's plenty of work to do
    - And I can't do it alone!
- If you maintain a worker library
    - Have interesting use cases
    - Or have been burned by one...
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# Let's chat!

<ul class="list-none! [&>li]:m-0!">
  <li><mdi-earth /> theorangeone.net</li>
  <li><mdi-github /> @RealOrangeOne</li>
  <li><mdi-twitter /> @RealOrangeOne</li>
  <li><mdi-mastodon /> @jake@theorangeone.net</li>
</ul>

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  <h3>Me</h3>
  <img src="/dls24-qrcode.png" width="150px" />
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  <h3><code>django-tasks</code></h3>
  <img src="/django-tasks-qrcode.png" width="150px" />
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