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Deploy - Flask

In this lesson we'll cover:

  • Pipfiles
  • Procfiles
  • Configuration

Prerequisites

Before we get started, we need a couple tools. Let's install a few things and set them up.

Pipenv

Install pipenv via your terminal.

pip install pipenv

Protip: Pipenv is a package that will help us manage Pipfiles. We can also install packages with pipenv, which will be similar to how regular pip install works, but it also automatically adds the package to the Pipfile.

Create Your Pipfile

Your Pipfile is a list of dependencies for your Flask app. It replaces the old way of keeping track of this, where you would use a freeze command to create a requirements.txt file. Now instead we will have Pipfile and Pipfile.lock. We'll cover the lock file in a moment. For now, let's set up your Pipfile.

Tip: You may see a lot of code on the internet that still uses requirements.txt. Remember, Pipfiles are a reaplcement for this. We do not need a requirements.txt!

What goes in the Pipfile?

According to the Pipenv docs, when you run the pipenv --python 3 command, if you don't have a Pipfile already, one will be generated for youthat looks like this:

[[source]]
url = "https://pypi.python.org/simple"
verify_ssl = true

[packages]

[requires]
python_version = "3.7"

This is a pretty good start. The only section we really need to put any thinking into is the [packages] section. Here, we just need to include any packages we actually import and use. This means, don't worry about sub-dependencies as they will be installed automatically!

Gunicorn

Gunicorn is a server that supports concurrent processes. It will make your Heroku app feel faster and be better utilized.

pipenv install gunicorn

The pipenv command above both installs gunicorn and adds it to the Pipfile. If you installed with the pip or pip3 commands, you will need to manually type the name gunicorn into your Pipfile. We're also going to want to type in flask as a package we are using. Your Pipfile should not look something like this:

[[source]]
name = "pypi"
url = "https://pypi.org/simple"
verify_ssl = true

[dev-packages]

[packages]
flask = "*"
gunicorn = "*"

[requires]
python_version = "3.7"

Solving Performance Issues: If after your app is up and running, you are experiencing performance issues, take a read through Heroku's Docs regarding Gunicorn and configure WEB_CONCURRENCY and/or preload settings accordingly.

Procfile

Now that we have Gunicorn installed, let's use it! Create a file called Procfile in the top level folder of you app.

Remember the capital P in Procfile!

Your Procfile should look like the following:

web: gunicorn server:app

The "server" in the above command refers to the name of your entry point. So, it assumes you called your main file server.py. If you called your main file app.py then it would look like web: gunicorn app:app

Tip: You can add a release step as well, which runs after the build succeeds. For example, this is often used for database migrations.

Deploy!

Now we're ready to deploy! Create a Heroku app, then add, commit, and push to Heroku.

heroku apps:create <your-app-name-here>
git add -A
git commit -m "Ready for deployment!"
git push heroku master

Configuration Variables

You can add configuration variables from the command line or via the GUI if you log into Heroku's website.

heroku config:set FLASK_ENV=production
heroku config:set FLASK_SECRET=SuperSecretKey

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