On this episode, we will look at what it takes to go live and how to prepare your Django project for the internet.

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Last Episode

On the last episode, we discussed how you can verify that your site works and continues to work. We dug into automated testing and how to write tests for your Django apps.

Pick A Python Application Server

When you begin to learn Django, the documentation will instruct you to use ./manage.py runserver to interact with your application locally. runserver is a great tool for getting started because you can avoid extra software from the outset of your Django journey.

While great, the runserver command is not designed for handling a lot of web traffic. runserver is explicitly intended for a development-only setting. Aside from a lack of performance tuning options, the server doesn’t receive the same security scrutiny as other Python web application servers.

These factors add up to make the runserver command unsuitable for handling your live site. What should you use instead? When you read the deployment documentation, you’ll find many possible Python web application servers listed. Gunicorn, uWSGI, Apache with mod_wsgi, Daphne, Hypercorn, and Uvicorn are all presented as available options. That’s way too much choice.

Use Gunicorn.

Gunicorn (which stands for “Green Unicorn”) is a very simple web application server to start using. In my experience, Gunicorn stays easy to use and works for projects that receive a ton of traffic. I’ve used some of the other options presented for Django apps, and few are as simple to use as Gunicorn.

$ gunicorn project.wsgi

By default, Gunicorn will only create a single worker process. The Gunicorn documentation recommends picking a number that is two to four times larger than the number of CPU cores available to your machine.

The number of workers is a large determining factor in how many requests that your Django app can handle at once. The number of requests processed is usually called traffic by web developers. The idea of handling more traffic by creating more processes (i.e., Gunicorn workers) is called horizontal scaling. In contrast, vertical scaling handles more traffic by using a better individual computer. A faster processor with a single CPU can handle more requests. When thinking about performance, horizontal scaling is often a far easier approach.

$ gunicorn project.wsgi --workers 2 --log-file -

Pick Your Cloud

Once you know which application server to use and how to use it, you need to run your code somewhere. Again, you can be paralyzed by the sheer volume of choices available to you. AWS, GCP, Azure, Digital Ocean, Linode, Heroku, PythonAnywhere, and so many other cloud vendors are out there and able to run your application.

If you’re getting started, use a Platform as a Service (PaaS) option. Specifically, I think Heroku is a great platform for applications. A PaaS removes loads of operational complexity that you may be unequipped to handle initially if you’re newer to web development.

Think you want to run your application on a general cloud provider like AWS? You can certainly do that, but you’ll potentially need to be prepared for:

• Setting up machines
• Getting TLS certificates for https
• Doing database backups
• Using configuration management tools to automate deployment
• And loads more!

Let’s contrast this with Heroku. Because Heroku is a PaaS, they deal with the vast majority of the setup and coordination of machines in their cloud. Your experience as a developer primarily moves to a single command:

$ git push heroku main

Project Preconditions

Django has a few preconditions that it expects before running your application in a live setting. If you’ve listened to the previous episodes, then you’ve actually heard most of these preconditions by now, but we’ll group them together in this section so you can see the complete picture.

One that we haven’t discussed is the DJANGO_SETTINGS_MODULE environment variable. This is one critical element to your application because the variable signals to your Django application where the settings module is located. If you have different settings modules for different configurations (e.g., a live site configuration versus a unit testing configuration), then you may need to specify which settings module that Django should use when running.

The next important precondition for your app is keeping your database in sync using migrations. As mentioned in the models episode, we make migrations when making model changes. These migrations generate instructions for your relational database, so that Django can match the database schema.

$ ./manage.py migrate

Heroku uses a Procfile to set which machines and commands to run so my Procfile looks like:

release: python manage.py migrate
web: gunicorn project.wsgi --workers 2 --log-file -

Another precondition needed for your app is static files. We saw in the static files episode that Django looks for static files in a single directory for performance reasons. That requires running a command to put those files in the expected location.

$ ./manage.py collectstatic

Protecting Your Site

Django includes a command that provides a set of instructive safety messages for things that you should apply to your site that are important. Thankfully, ignoring these messages is unlikely to affect your personal health, but the messages are valuable to help you combat the bad forces that exist on the public internet.

To view these important messages, run:

$ ./manage.py check --deploy --fail-level WARNING
SystemCheckError: System check identified some issues:

WARNINGS:
?: (security.W004) You have not set a value for the SECURE_HSTS_SECONDS
  setting. If your entire site is served only over SSL, you may want to
  consider setting a value and enabling HTTP Strict Transport Security.
  Be sure to read the documentation first; enabling HSTS carelessly can
  cause serious, irreversible problems.
?: (security.W008) Your SECURE_SSL_REDIRECT setting is not set to True.
  Unless your site should be available over both SSL and non-SSL connections,
  you may want to either set this setting True or configure a load balancer
  or reverse-proxy server to redirect all connections to HTTPS.
?: (security.W012) SESSION_COOKIE_SECURE is not set to True. Using a
  secure-only session cookie makes it more difficult for network traffic
  sniffers to hijack user sessions.
?: (security.W016) You have 'django.middleware.csrf.CsrfViewMiddleware'
  in your MIDDLEWARE, but you have not set CSRF_COOKIE_SECURE to True.
  Using a secure-only CSRF cookie makes it more difficult for network traffic
  sniffers to steal the CSRF token.
?: (security.W018) You should not have DEBUG set to True in deployment.
?: (security.W020) ALLOWED_HOSTS must not be empty in deployment.

System check identified 6 issues (0 silenced).

The items reported by the checklist are often about settings that could be configured better. These checks are created by the System check framework that comes with Django.

Some of these checks are too modest about their importance. For instance, security.W018 is the warning that tells you that DEBUG is set to True in the settings. DEBUG = True is TERRIBLE for a live site since it can trivially leak loads of private data.

If HSTS is handled elsewhere, you could set the SILENCED_SYSTEM_CHECKS setting to tell Django that you took care of it.

# project/settings.py

SILENCED_SYSTEM_CHECKS = ["security.W004"]

Prepare For Errors

Dealing with a live site brings a new set of challenges. Try as we might to consider every possible action that our users do, we’ll never get them all. There are lots of ways that a site can have errors from things that we failed to consider. Since errors will happen with a large enough product and large enough customer base, we need some plan to manage them.

We can consider a few strategies:

1. Do nothing.

While I don’t recommend this strategy, you could wait for your customers to report errors to you. Some portion of customers might actually write to you and report a problem, but the vast majority won’t. What’s worse is that some of these customers may abandon your product if the errors are bad enough or frequent enough.

Using your customers to learn about errors makes for a poor user experience.

2. Use error emails.

The Django deployment documentation highlights Django’s ability to send error information to certain email addresses. I don’t recommend this strategy either. Why?

• Setting up email properly can be a very tricky endeavor that involves far more configuration than you may realize. You may need email for your service, but setting it up for error info alone is overkill.
• The error emails can include Python tracebacks to provide context, but other tools can provide much richer context information (e.g., the browser used when a customer experiences an error).
• If you have a runaway error that happens constantly on your site, you can say “bye, bye” to your email inbox. A flood of emails is a quick way to get email accounts flagged and hurt the deliverability of email.

3. Use an error tracking service.

Error tracking services are specifically designed to collect context about errors, aggregate common errors together, and generally give you tools to respond to your site’s errors appropriately.

In the Django world, I generally hear about two of these error tracking services: Rollbar and Sentry. I’ve used both of these error trackers, and I think they are both great. For my personal projects, I happen to pick Rollbar by default, so I’ll describe that service in this section as an example.

The flow for installing Rollbar is:

1. Create a Rollbar account on their site.
2. Install the rollbar package.
3. Set some settings in a ROLLBAR dictionary.

# project/settings.py

ROLLBAR = {
    "enabled": env("ROLLBAR_ENABLED"),
    "access_token": env("ROLLBAR_ACCESS_TOKEN"),
    "environment": env("ROLLBAR_ENVIRONMENT"),
    "branch": "master",
    "root": BASE_DIR,
}

Once you set this up, how can you tell that it’s working? Like a musician tapping a microphone to see if it’s working, I like to add a view to my code that let’s me test that my error tracking service is operational.

# application/views.py

from django.contrib.admin.views.decorators import staff_member_required

@staff_member_required
def boom(request):
    """This is for checking error handling (like Rollbar)."""
    raise Exception("Is this thing on?")

With error tracking set up, you’ll be in a good position to see errors when they happen on your site. In fact, a great way to win the favor of customers can be to fix errors proactively and reach out to them. Most people don’t enjoy contacting support and would be surprised and delighted if you tell them that you fixed their problem immediately.

Summary

In this episode, we learned the things to consider when deploying a site to the internet. We examined:

• Deploying your application with a Python web application server (i.e., ./manage.py runserver isn’t meant for deployed apps)
• Running your app on a cloud vendor
• Deployment preconditions for managing settings, migrations, and static files
• A checklist to confirm that your settings are configured with the proper security guards
• Monitoring your application for errors

Next Time

On the next episode, we are going to look at session data. Sessions are a way to keep a bit of data for each visitor to your site. We’ll see why sessions are critical to most Django apps and what that data is used for.

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