Async Django in Production
jonathanadly.com
jonathanadly.com
Four releases later async will be marketed as "this has been a mistake" and the green threads will be the best thing ever. Thousands of blog posts will be written and everyone has to rewrite their code bases. Repeat for goroutines etc.
I haven't tried Async Django, (But use normal Django on a few work and hobby project) and am hesitant based on my experience in rust, and not finding a fault I think coloring my Python/Django code would be advantageous to do.
But there is a big downside, that's true.
Async functions allow me to build massively parallel and concurrent systems with ease - it's beautiful.
In comparison, I'm not as fond of Go's approach to concurrency, which feels less elegant to me.
python users only have themselves to blame for ignoring it.
> IIRC the history of the async things in TLA in order: Twisted (callbacks), Eventlet (for Second Life by Linden Labs), tornado, gevent; gunicorn, Python 3.5+ asyncio, [uvicorn,]
Async/await > History: https://en.wikipedia.org/wiki/Async/await
However, if we are to be honest, the history of async usage in Django wasn't very impressive. You could argue that for most products, you don’t really need async. It was just an extra layer of complexity without any significant practical benefit.
Over the last couple of years, AI use-cases have changed that perception. Many AI products have calling external APIs over the network as their bottleneck. This makes the complexity from async Python worth considering. FastAPI with its intuitive async usage and simplicity have risen to be the default API/web layer for AI projects.
I wrote about using async Django in a relatively complex AI open source project here: https://jonathanadly.com/is-async-django-ready-for-prime-tim...
tldr: Async django is ready! there is a couple of gotcha's here and there, but there should be no performance loss when using async Django instead of FastAPI for the same tasks. Django's built-in features greatly simplify and enhance the developer experience.
So - go ahead and use async Django in your next project. It should be a lot smoother that it was a year or even six months ago.
Can you expand more on why these AI cases make the complexity tradeoff different?
I'd imagine think waiting on a 3rd party LLM API call would be computationally very inexpensive compared to what's going on at the business end of that API call. Further lowering the cost, Django is usually configured to use multiple threads and/or processes so that this blocking call won't keep a CPU idle, no?
To restate my comment: I argued (1) this CPU cost would be very marginal compared to the LLM API compute cost, and (2) the CPU blocking claim doesn't really hold, due to the wonders of threads and processes.
1. A blocking call, which can take 3-10 seconds.
2. A streaming call, which can also take 3-10 seconds but where the content is streaming directly to you as it is generated (and you may be proxying it through to your user).
In both cases you risk blocking a thread or process for several seconds. That's the problem asyncio solves for you - it means you could have hundreds (or even thousands) of users all waiting for the response to that LLM call without needing hundreds or thousands of blocked threads/processes.
Or maybe the disconnect is where I'm taking for granted that "cost of parked thread" is the same as worrying about the nr of parked threads? Maybe everyone uses Django setups where it's nontrivial to add memory, increase serverless platform limits, etc if you get the happy problem of 10k concurrent users? Or maybe people don't know that the nr of threads/processes you can have on Linux is much more than hundreds or thousands. Or maybe there's some Python or Django specific limits to this.
See eg https://www.baeldung.com/linux/max-threads-per-process for some runtime sysctl knobs if you want to go higher than the default limits. (Though the section 6 there seems out of date and written with the 32-bit OS in mind)
[1] as reported by the Python snippet from https://stackoverflow.com/a/64406494
They’re very slow. Like, several seconds to get a response slow. If you’re serving a very large number of very fast requests, you can argue that the simplicity of the sync model makes it worth it to just scale up the number of processes required to serve that many requests, but the LLM calls are slow enough that it means you need to dramatically scale up the number of serving processes available if you’re going to keep the sync model, and that’s mostly to have CPUs sitting around idle waiting for the LLM to come back. The async model can also let you parallelize calls to the LLMs if you’re making multiple independent calls within the same request - this can cut multiple seconds off your response time.
If the alternative to Async is more processes, rather than threads, a clear benefit is reduced memory usage and reduced process startup time.
Not necessarily true. Many process-parallel Python environments support using fork(2) for parallelism (multiprocessing, gunicorn, celery).
For similar processes (e.g. parallel waiting on RPCs) that removes the memory overhead. It also largely mitigates startup time costs (especially if forks are reused for multiple requests, which they are in most forking contexts).
While there is debate and grumbling in the Python community about fork(2)’s rough edges re: signals/threads/MacOS, these issues are usually handled inside parallelism-management library code and rarely concern application level developers.
People who like synchronous Python can use Django.
People who like asynch Python can use Starlette - the async web server also written by the guy who wrote Django.
It’s not clear why Django needs to be async, especially when I get the sense there’s developers who like async and developers who prefer synch. It’s a natural fit for Django to fulfill the sync demand and Starlette to fulfill the async. They’re both good.
Django has a batteries-includes approach, benefits from tighter integration of orm, auth, form handling, etc, and has a huge 3rd party ecosystem.
First-class async support in Django allows Django users to avoid jumping through hoops (celery, channels, ...) for longer-running requests, something especially noticable if you're calling any kind of AI service.
Django is fine for writing a thin CRUD layer around a database. It makes the easy stuff easy. But doesn't seem to help much for the hard stuff and often actively hinders it.
Really the main reason for Django is its ORM and migrations. It's basically the other Python ORM (next to SQLAlchemy) but, unlike SQLAlchemy, it's not designed to be used standalone. In my experience I find Django (and active record ORMs in general) easier for people to get started with, but massively limiting in long run for complex domains.
This assumes that people don't do multi-page apps or sites any more, which ... isn't true. And I believe django-ninja replaces forms/serialization/deserialization and routing, while nicely integrating with everything else.
> Django is fine for writing a thin CRUD layer around a database.
In my dozen or so years with Django, I confess I did more than a few thin CRUD layers around a database. But also worked on billing systems for telecoms, insurance provider API services, live/on demand audio/video streaming services, a bunch of business process apps, AI codegen tools, and other web apps and API backends that were way more than thin CRUD layers around databases.
Django was rarely a hindrance. In fact, Python being sync-only (or Django not supporting async) was usually more of a hindrance that anything Django specific.
> In my experience I find Django (and active record ORMs in general) easier for people to get started with, but massively limiting in long run for complex domains.
In my exprience the only situations where Django's ORM doesn't help much is when you have a lot of business logic in your database (views, stored procedures), or the database is organized in a way that's not Django's preffered way. Still works, mind you, just not as great a experience. However, the vast majority of projects I've encountered have none of those.
Otherwise, I've found its ORM quite powerful, and easy to drop down to raw() in cases where you really need it (which was maybe 1% on the projects I've worked).
+1 on this. Django scales pretty well when adopting a clean architecture like Django Model Behaviours with mixins.
> Otherwise, I've found its ORM quite powerful.
Same. In ten years, the only issue I had is with a very complex query that the ORM was not able to write properly. But a workaround existed.
I'm currently using FastAPI in a project. It's very enjoyable (especially with a strictly typed codebase) but I have to write lots of batteries by myself, which is not very productive (unless you keep this boilerplate code for future projects).
Finally, in my opinion, the best reason to not use Django is not the project itself (because it will do the job in 99% case), it's because all you learn is tied to Django.
Having learn Pydantic recently was a breed of fresh air, and I would reuse it in lots of projects, not only web projects.
Quick, where would you put a high-level business function that touches multiple models? Where would you put the model-level validation for that? I've seen all of the following: in a view, in a form, in a service-layer function, arbitrarily in one of the models/managers, implicitly in the database schema (just catch the IntegrityErrror!).
There are endless discussions online about where to do this. This isn't a good sign. It should be easy. The business logic should be at the heart of an application. But instead we see Django's ORM at the heart.
Django models are really limiting and totally tied to the database. You can't even have a model that has a list/set of items without getting into ForeignKeys etc. You can't test any of it without having the database present. Why would I need the database to be there to test business logic?! The point of an ORM is to do object persistence, not to do business logic.
So I've seen people do a separate set of ORM models and domain models and then manually mapping between them. This is possible, but it's a whole lot easier with something like SQLAlchemy which is actually designed for that (it's a data mapper rather than active record type ORM).
Then there's stuff like django-admin and ModelForms etc. which are the last thing you want if you're doing more than CRUD.
Tbh it would be utterly remarkable if Django somehow made this stuff easy. But it doesn't and I find myself wishing I just put in the effort to set up the boring stuff like auth etc. but with a proper architecture.
It's just python: `descriptive_name.py`. `ingest_validation.py` etc. If this seems too terse, it's because your question was posed in a general way. If you have more info on the sort of business logic you have in mind, or the sort of data validation, I'll reply with more.
Could you describe what you have in mind regarding models not tied to the database? If it's the naive interpretation I'm thinking of, use python dataclasses and enums. Django models are specifically to represent database schema.
Reading between the lines, perhaps you are looking for something not covered by a web framework? Django's features are for responding to HTTP requests, managing a relational database, auth, email, admin, templates etc. If you're trying to do something not part of this, use other parts of the Python language. Django is a library; Python is the more fundamental tool used to build applications.
You could use Django like this, but you'd end up manually mapping between Django models and high-level domain models. But this mapping is exactly what an ORM like SQLAlchemy does! It seems crazy to do it yourself. So nobody does. They build fat models with all the business logic right next to application logic like foreign keys etc.
Even if you did try to do something different developers would complain that it's no longer a "Django project". Have you ever seen any Django project do business logic completely independently of application logic?
If you really prefer SQLAlchemy, there is nothing stopping you from using it over the Django ORM, I happen to prefer the Django ORM, but Django doesn't get jealous if you go out with a different ORM (it is a polyamorious web framework[1]).
Yes, I have seen Django applications do that. There are plenty of individuals out there advocating such a separation. I wouldn't worry about these "different developers' and their opinions.
[1] I was going to use a smiley face here, but then I recalled that a Python dev was de-flocked recently for using smiley emoji as it is offensive to some individuals, so insert whatever words or symbols you don't find offensive that indicate humor instead.
Using Django without its ORM really doesn't seem attractive. I'm really not sure what you'd be getting from Django at that point. Crap templates, views that aren't views. The ORM is the only good bit of Django. Well, that and the package ecosystem.
The more I think about it the more I realise it's that last point that is the real attraction.
Also please don't worry about offending me. I come from the old internet ;)
Which is a very Django way to think: lots of tools ready to go, use only what you need.
Django having async support means you can use the Django ORM, and the Django request/response cycle, and generally not need to write your async and your sync web code using slightly different APIs.