Getting Started on Heroku with Python

Introduction

This tutorial will have you deploying a Python app (a simple Django app) in minutes.

Hang on for a few more minutes to learn how it all works, so you can make the most out of Heroku.

The tutorial assumes that you have:

• a free Heroku account.
• Python version 3.10 installed locally - see the installation guides for OS X, Windows, and Linux.
• Postgres installed locally, if running the app locally.

Set up

In this step you’ll install the Heroku Command Line Interface (CLI). You use the CLI to manage and scale your applications, provision add-ons, view your application logs, and run your application locally.

Download and run the installer for your platform:

Once installed, you can use the heroku command from your command shell.

Use the heroku login command to log in to the Heroku CLI:

$ heroku login
heroku: Press any key to open up the browser to login or q to exit
 ›   Warning: If browser does not open, visit
 ›   https://cli-auth.heroku.com/auth/browser/***
heroku: Waiting for login...
Logging in... done
Logged in as me@example.com

This command opens your web browser to the Heroku login page. If your browser is already logged in to Heroku, simply click the Log in button displayed on the page.

This authentication is required for both the heroku and git commands to work correctly.

Prepare the app

In this step, you will prepare a simple application that can be deployed.

Before continuing, make sure Git is installed (see Set up).

To clone the sample application so that you have a local version of the code that you can then deploy to Heroku, execute the following commands in your local command shell or terminal:

$ git clone https://github.com/heroku/python-getting-started.git
$ cd python-getting-started

You now have a functioning git repository that contains a simple application, a runtime.txt specifying which Python version will be used, and a requirements.txt, which is used by Python’s dependency manager, Pip.

Deploy the app

In this step you will deploy the app to Heroku.

Before continuing, make sure both Git and the Heroku CLI are installed (see Set up).

Create an app on Heroku, which prepares Heroku to receive your source code:

$ heroku create
Creating app... done, ⬢ serene-caverns-82714
https://serene-caverns-82714.herokuapp.com/ | https://git.heroku.com/serene-caverns-82714.git

When you create an app, a git remote (called heroku) is also created and associated with your local git repository.

Heroku generates a random name (in this case serene-caverns-82714) for your app, or you can pass a parameter to specify your own app name.

Now deploy your code:

$ git push heroku main
Enumerating objects: 509, done.
Counting objects: 100% (509/509), done.
Delta compression using up to 12 threads
Compressing objects: 100% (238/238), done.
Writing objects: 100% (509/509), 94.80 KiB | 94.80 MiB/s, done.
Total 509 (delta 234), reused 509 (delta 234), pack-reused 0
remote: Compressing source files... done.
remote: Building source:
remote:
remote: -----> Building on the Heroku-20 stack
remote: -----> Determining which buildpack to use for this app
remote: -----> Python app detected
remote: -----> Using Python version specified in runtime.txt
remote: -----> Installing python-3.10.4
remote: -----> Installing pip 21.3.1, setuptools 57.5.0 and wheel 0.37.0
remote: -----> Installing SQLite3
remote: -----> Installing requirements with pip
remote:        Collecting django
remote:          Downloading Django-4.0.1-py3-none-any.whl (8.0 MB)
remote:        Collecting gunicorn
remote:          Downloading gunicorn-20.1.0-py3-none-any.whl (79 kB)
remote:        Collecting django-heroku
remote:          Downloading django_heroku-0.3.1-py2.py3-none-any.whl (6.2 kB)
remote:        Collecting asgiref<4,>=3.4.1
remote:          Downloading asgiref-3.4.1-py3-none-any.whl (25 kB)
remote:        Collecting sqlparse>=0.2.2
remote:          Downloading sqlparse-0.4.2-py3-none-any.whl (42 kB)
remote:        Collecting psycopg2
remote:          Downloading psycopg2-2.9.3.tar.gz (380 kB)
remote:          Preparing metadata (setup.py): started
remote:          Preparing metadata (setup.py): finished with status 'done'
remote:        Collecting dj-database-url>=0.5.0
remote:          Downloading dj_database_url-0.5.0-py2.py3-none-any.whl (5.5 kB)
remote:        Collecting whitenoise
remote:          Downloading whitenoise-5.3.0-py2.py3-none-any.whl (19 kB)
remote:        Building wheels for collected packages: psycopg2
remote:          Building wheel for psycopg2 (setup.py): started
remote:          Building wheel for psycopg2 (setup.py): finished with status 'done'
remote:          Created wheel for psycopg2: filename=psycopg2-2.9.3-cp310-cp310-linux_x86_64.whl size=586593 sha256=25ea6b40570d00fb7329c9691e557245a1050857323893e93068f0f07ecef238
remote:          Stored in directory: /tmp/pip-ephem-wheel-cache-d5wzowyy/wheels/81/b6/3d/091aad3e8919ea76c84c2674b02ce3ab52de882e091c39249e
remote:        Successfully built psycopg2
remote:        Installing collected packages: sqlparse, asgiref, whitenoise, psycopg2, django, dj-database-url, gunicorn, django-heroku
remote:        Successfully installed asgiref-3.4.1 dj-database-url-0.5.0 django-4.0.1 django-heroku-0.3.1 gunicorn-20.1.0 psycopg2-2.9.3 sqlparse-0.4.2 whitenoise-5.3.0
remote: -----> $ python manage.py collectstatic --noinput
remote:        129 static files copied to '/tmp/build_a5ccf75d/staticfiles', 379 post-processed.
remote:
remote: -----> Discovering process types
remote:        Procfile declares types -> web
remote:
remote: -----> Compressing...
remote:        Done: 68.1M
remote: -----> Launching...
remote:        Released v5
remote:        https://serene-caverns-82714.herokuapp.com/ deployed to Heroku
remote:
remote: Verifying deploy... done.
To https://git.heroku.com/serene-caverns-82714.git
 * [new branch]      revert-to-requirements -> main

The application is now deployed. Ensure that at least one instance of the app is running:

$ heroku ps:scale web=1

If when running the ps:scale command above you see the error “Couldn't find that process type (web)”, it means the first deploy of the application is taking a bit longer than normal, and the command should be repeated after waiting a few minutes.

Now visit the app at the URL generated by its app name. As a handy shortcut, you can open the website as follows:

$ heroku open

View logs

Heroku treats logs as streams of time-ordered events aggregated from the output streams of all your app and Heroku components, providing a single channel for all of the events.

View information about your running app using one of the logging commands, heroku logs --tail:

$ heroku logs --tail
2022-01-19T16:49:40.323576+00:00 heroku[web.1]: Starting process with command `gunicorn gettingstarted.wsgi`
2022-01-19T16:49:41.952853+00:00 app[web.1]: [2022-01-19 16:49:41 +0000] [4] [INFO] Starting gunicorn 20.1.0
2022-01-19T16:49:41.953307+00:00 app[web.1]: [2022-01-19 16:49:41 +0000] [4] [INFO] Listening at: http://0.0.0.0:5021 (4)
2022-01-19T16:49:41.954552+00:00 app[web.1]: [2022-01-19 16:49:41 +0000] [4] [INFO] Using worker: sync
2022-01-19T16:49:41.962918+00:00 app[web.1]: [2022-01-19 16:49:41 +0000] [9] [INFO] Booting worker with pid: 9
2022-01-19T16:49:41.992997+00:00 app[web.1]: [2022-01-19 16:49:41 +0000] [10] [INFO] Booting worker with pid: 10
2022-01-19T16:49:42.380291+00:00 heroku[web.1]: State changed from starting to up
2022-01-19T16:49:44.000000+00:00 app[api]: Build succeeded
2022-01-19T16:56:43.488176+00:00 heroku[router]: at=info method=GET path="/" host=serene-caverns-82714.herokuapp.com request_id=df14c065-0d94-45b7-b21e-6e69a0ad93e2 fwd="123.45.67.89" dyno=web.1 connect=0ms service=31ms status=200 bytes=7719 protocol=https

Visit your application in the browser again, and you’ll see another log message generated.

Press Control+C to stop streaming the logs.

Define a Procfile

Use a Procfile, a text file in the root directory of your application, to explicitly declare what command should be executed to start your app.

The Procfile in the example app you deployed looks like this:

web: gunicorn gettingstarted.wsgi

This declares a single process type, web, and the command needed to run it. The name web is important here. It declares that this process type will be attached to the HTTP routing stack of Heroku, and receive web traffic when deployed.

Procfiles can contain additional process types. For example, you might declare one for a background worker process that processes items off of a queue.

Microsoft Windows

The sample app has an additional Procfile for local development on Microsoft Windows, located in the file Procfile.windows. Later tutorial steps will use this instead: it starts a different web server, one that is compatible with Windows.

web: python manage.py runserver 0.0.0.0:5000

Scale the app

Right now, your app is running on a single web dyno. Think of a dyno as a lightweight container that runs the command specified in the Procfile.

You can check how many dynos are running using the ps command:

$ heroku ps
Free dyno hours quota remaining this month: 999h 50m (99%)
Free dyno usage for this app: 0h 0m (0%)
For more information on dyno sleeping and how to upgrade, see:
https://devcenter.heroku.com/articles/dyno-sleeping

=== web (Free): gunicorn gettingstarted.wsgi (1)
web.1: up 2022/01/19 16:49:42 +0000 (~ 3m ago)

By default, your app is deployed on a free dyno. Free dynos will sleep after a half hour of inactivity (if they don’t receive any traffic). This causes a delay of a few seconds for the first request upon waking. Subsequent requests will perform normally. Free dynos also consume from a monthly, account-level quota of free dyno hours - as long as the quota is not exhausted, all free apps can continue to run.

To avoid dyno sleeping, you can upgrade to a hobby or professional dyno type as described in the Dyno Types article. For example, if you migrate your app to a professional dyno, you can easily scale it by running a command telling Heroku to execute a specific number of dynos, each running your web process type.

Scaling an application on Heroku is equivalent to changing the number of dynos that are running. Scale the number of web dynos to zero:

$ heroku ps:scale web=0
Scaling dynos... done, now running web at 0:Free

Access the app again by hitting refresh on the web tab, or heroku open to open it in a web tab. You will get an error message because you no longer have any web dynos available to serve requests.

Scale it up again:

$ heroku ps:scale web=1
Scaling dynos... done, now running web at 1:Free

For abuse prevention, scaling a non-free application to more than one dyno requires account verification.

Install app dependencies locally

Heroku recognizes an app as a Python app by looking for key files. Including a requirements.txt in the root directory is one way for Heroku to recognize your Python app.

The demo app you deployed already has a requirements.txt, and it looks something like this:

django
gunicorn
django-heroku

The requirements.txt file lists the app dependencies together. When an app is deployed, Heroku reads this file and installs the appropriate Python dependencies using the pip install -r command.

To install the dependencies locally, we first want to create a “Virtual Environment” (also known as a “venv”) into which we can install the packages without affecting your system Python installation. To do this, run the following command:

$ python3 -m venv --upgrade-deps venv

Next, the virtual environment needs to be activated.

If you’re on a Microsoft Windows system, activate the venv using:

.\venv\Scripts\activate

Or if you’re on a macOS/Linux system, activate the venv using:

source venv/bin/activate

For help with setting up a virtual environment, see the Python documentation.

Finally, the dependencies can now be installed into the newly created environment:

$ pip install -r requirements.txt

Note: Postgres must be properly installed in order for this step to work properly. If you’re running Linux, the libpq-dev system package (or equivalent for your distribution) must also be installed.

Installing the dependencies also caused several other dependencies to be installed. You can see them by using pip’s feature list:

$ pip list
Package         Version
--------------- -------
asgiref         3.4.1
dj-database-url 0.5.0
Django          4.0.1
django-heroku   0.3.1
gunicorn        20.1.0
pip             21.3.1
psycopg2        2.9.3
setuptools      59.5.0
sqlparse        0.4.2
wheel           0.37.0
whitenoise      5.3.0

Once dependencies are installed, you will be ready to run your app locally.

Run the app locally

Before continuing, make sure the app’s dependencies have been installed locally.

The app is almost ready to start locally. Django uses local assets, so first, you’ll need to run collectstatic:

$ python manage.py collectstatic

Respond with “yes”.

Now start your application locally using heroku local, which was installed as part of the Heroku CLI.

If you’re on a Microsoft Windows system, run this:

$ heroku local -f Procfile.windows

Or if you’re on a macOS/Linux system, use the default Procfile by running:

$ heroku local

Your local web server will then start up:

[OKAY] Loaded ENV .env File as KEY=VALUE Format
17:39:12 web.1   |  [2022-01-19 17:39:12 +0000] [18471] [INFO] Starting gunicorn 20.1.0
17:39:12 web.1   |  [2022-01-19 17:39:12 +0000] [18471] [INFO] Listening at: http://0.0.0.0:5000 (18471)
17:39:12 web.1   |  [2022-01-19 17:39:12 +0000] [18471] [INFO] Using worker: sync
17:39:12 web.1   |  [2022-01-19 17:39:12 +0000] [18472] [INFO] Booting worker with pid: 18472

If you see “Connection in use” errors, check that no other running programs are using port 5000. On macOS Monterey, Airplay Receiver runs on port 5000 and will need to be disabled by going to System Preferences -> Sharing and then unticking “Airplay Receiver”.

Just like Heroku, heroku local examines the Procfile to determine what to run.

Open http://localhost:5000 with your web browser. You should see your app running locally.

If you see “Not Found” errors in your console, check that the collectstatic step above was run before starting the web server.

To stop the app from running locally, go back to your terminal window and press Ctrl+C to exit.

Push local changes

In this step you’ll learn how to propagate a local change to the application through to Heroku. As an example, you’ll modify the application to add an additional dependency and the code to use it.

Add the requests package to your requirements.txt file:

django
gunicorn
django-heroku
requests

And then use pip to install the requests package via the updated requirements.txt file:

$ pip install -r requirements.txt

Modify hello/views.py so that it imports the requests module at the start:

import requests

Now modify the index method to make use of the module. Try replacing the current index method with the following code:

def index(request):
    r = requests.get('https://httpbin.org/status/418')
    print(r.text)
    return HttpResponse('<pre>' + r.text + '</pre>')

Now test again locally.

If you’re on a Microsoft Windows system, run this:

$ heroku local -f Procfile.windows

Or if you’re on a macOS/Linux system, use the default Procfile by running:

$ heroku local

Visit your application at http://localhost:5000. You should now see the output of fetching http://httpbin.org/status/418, which is a lovely teapot:

    -=[ teapot ]=-

       _...._
     .'  _ _ `.
    | ."` ^ `". _,
    \_;`"---"`|//
      |       ;/
      \_     _/
        `"""`

If instead you see the error ModuleNotFoundError: No module named 'requests', check that the steps to install the requests package above were completed successfully.

Now deploy. Almost every deploy to Heroku follows this same pattern. First, add the modified files to the local git repository:

$ git add .

Now commit the changes to the repository:

$ git commit -m "Demo"

Now deploy, just as you did previously:

$ git push heroku main

Finally, check that everything is working:

$ heroku open

Provision add-ons

Add-ons are third-party cloud services that provide out-of-the-box additional services for your application, from persistence through logging to monitoring and more.

By default, Heroku stores 1500 lines of logs from your application. However, it makes the full log stream available as a service - and several add-on providers have written logging services that provide things such as log persistence, search, and email and SMS alerts.

In this step you will provision one of these logging add-ons, Papertrail.

To help with abuse prevention, provisioning an add-on requires account verification. If your account has not been verified, you will be directed to visit the verification site, to add a credit-card to your account. This credit card will only be charged if you use paid Heroku features - the default Papertrail plan is free.

Provision the papertrail logging add-on:

$ heroku addons:create papertrail
Creating papertrail on ⬢ serene-caverns-82714... free
Welcome to Papertrail. Questions and ideas are welcome (technicalsupport@solarwinds.com). Happy logging!
Created papertrail-convex-88929 as PAPERTRAIL_API_TOKEN
Use heroku addons:docs papertrail to view documentation

The add-on is now deployed and configured for your application. You can list add-ons for your app like so:

$ heroku addons

To see this particular add-on in action, visit your application’s Heroku URL a few times. Each visit will generate more log messages, which should now get routed to the papertrail add-on. Visit the papertrail console to see the log messages:

$ heroku addons:open papertrail

Your browser will open up a Papertrail web console, showing the latest log events. The interface lets you search and set up alerts:

Start a console

You can run a command, typically scripts and applications that are part of your app, in a one-off dyno using the heroku run command. It can also be used to launch a REPL process attached to your local terminal for experimenting in your app’s environment:

$ heroku run python manage.py shell
Running python manage.py shell on ⬢ serene-caverns-82714... up, run.9594 (Free)
Python 3.10.3 (main, Jan 14 2022, 23:41:42) [GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>>

If you receive an error, Error connecting to process, then you may need to configure your firewall.

The Python shell is running in the context of your app and all its dependencies. From here you can import some of your application files. For example, you will be be able to run the following:

>>> import requests
>>> print(requests.get('https://httpbin.org/status/418').text)

    -=[ teapot ]=-

       _...._
     .'  _ _ `.
    | ."` ^ `". _,
    \_;`"---"`|//
      |       ;/
      \_     _/
        `"""`

To exit the Python shell, run the command exit().

To get a real feel for how dynos work, you can create another one-off dyno and run the bash command, which opens up a shell on that dyno. You can then execute commands there. Each dyno has its own ephemeral filespace, populated with your app and its dependencies - once the command completes (in this case, bash), the dyno is removed.

$ heroku run bash
Running bash on ⬢ serene-caverns-82714... up, run.3789 (Free)
~ $ ls
app.json  gettingstarted  hello  manage.py  Procfile  Procfile.windows  README.md  requirements.txt  runtime.txt  staticfiles
~ $ exit
exit

Don’t forget to type exit to exit the shell and terminate the dyno.

Define config vars

Heroku lets you externalise configuration - storing data such as encryption keys or external resource addresses in config vars.

At runtime, config vars are exposed as environment variables to the application.

Edit hello/views.py. At the beginning, add a line to import the os module:

import os

Now modify the index method so that it repeats an action depending on the value of the TIMES environment variable:

def index(request):
    times = int(os.environ.get('TIMES', 3))
    return HttpResponse('Hello! ' * times)

heroku local will automatically set up the environment based on the contents of the .env file in your local directory. In the top-level directory of your project there is already a .env file that has the following contents:

TIMES=2

If you run the app with heroku local and then visit http://localhost:5000, you’ll see two “Hello!”‘s.

To set the config var on Heroku, execute the following:

$ heroku config:set TIMES=2

View the config vars that are set using heroku config:

$ heroku config
=== serene-caverns-82714 Config Vars
DATABASE_URL:         postgres://aadoybxpeabguh:<PASSWORD>@ec2-3-216-113-109.compute-1.amazonaws.com:5432/d8pcm30gp3rago
PAPERTRAIL_API_TOKEN: <SECRET_TOKEN>
TIMES:                2

Deploy your changed application to Heroku to see this in action.

Provision a database

The add-on marketplace has a large number of data stores, from Redis and MongoDB providers, to Postgres and MySQL. In this step you will learn about the free Heroku Postgres add-on that was automatically provisioned when your app was deployed.

A database is an add-on, and so you can find out a little more about the database provisioned for your app using the addons command in the CLI:

$ heroku addons
Add-on                                      Plan       Price  State
──────────────────────────────────────────  ─────────  ─────  ───────
heroku-postgresql (postgresql-cubed-97628)  hobby-dev  free   created
 └─ as DATABASE
...

Listing the config vars for your app will display the URL that your app is using to connect to the database, DATABASE_URL:

$ heroku config
=== serene-caverns-82714 Config Vars
DATABASE_URL:         postgres://aadoybxpeabguh:<PASSWORD>@ec2-3-216-113-109.compute-1.amazonaws.com:5432/d8pcm30gp3rago
...

Heroku also provides a pg command that shows a lot more:

$ heroku pg
=== DATABASE_URL
Plan:                  Hobby-dev
Status:                Available
Connections:           0/20
PG Version:            13.5
Created:               2022-01-19 16:49 UTC
Data Size:             7.9 MB/1.00 GB (In compliance)
Tables:                0
Rows:                  0/10000 (In compliance) - refreshing
Fork/Follow:           Unsupported
Rollback:              Unsupported
Continuous Protection: Off
Add-on:                postgresql-cubed-97628

This indicates I have a hobby database (free), running Postgres 13.5, with no data.

The example app you deployed already has database functionality, which you should be able to reach by visiting your app’s URL and appending /db. For example, if your app was deployed to https://wonderful-app-287.herokuapp.com/ then visit https://wonderful-app-287.herokuapp.com/db.

However, accessing it now will yield a relation "hello_greeting" does not exist error, because while the database is configured, the tables have not yet been created.

To create the hello_greeting table, run the standard Django manage.py migrate command:

$ heroku run python manage.py migrate
Running python manage.py migrate on ⬢ serene-caverns-82714... up, run.4231 (Free)
System check identified some issues:

WARNINGS:
hello.Greeting: (models.W042) Auto-created primary key used when not defining a primary key type, by default 'django.db.models.AutoField'.
    HINT: Configure the DEFAULT_AUTO_FIELD setting or the AppConfig.default_auto_field attribute to point to a subclass of AutoField, e.g. 'django.db.models.BigAutoField'.
Operations to perform:
  Apply all migrations: admin, auth, contenttypes, hello, sessions
Running migrations:
  Applying contenttypes.0001_initial... OK
...

Now access the /db route again and you’ll see a simple page update every time you access it:

Page View Report

Jan. 19, 2022, 6:12 p.m.
Jan. 19, 2022, 6:17 p.m.

The code to access the database is straightforward, and makes use of a simple Django model called Greetings that you can find in hello/models.py.

Whenever you visit the /db route of your app, the following method in the hello/views.py file is invoked which creates a new Greeting and then renders all the existing Greetings:

def db(request):

    greeting = Greeting()
    greeting.save()

    greetings = Greeting.objects.all()

    return render(request, 'db.html', {'greetings': greetings})

Assuming that you have Postgres installed locally, use the heroku pg:psql command to connect to the remote database and see all the rows:

$ heroku pg:psql
--> Connecting to postgresql-cubed-97628
psql (14.1, server 13.5 (Ubuntu 13.5-2.pgdg20.04+1))
SSL connection (protocol: TLSv1.3, cipher: TLS_AES_256_GCM_SHA384, bits: 256, compression: off)
Type "help" for help.

serene-caverns-82714::DATABASE=>

Read more about Heroku PostgreSQL.

A similar technique can be used to install MongoDB or Redis add-ons.

Next steps

You now know how to deploy an app, change its configuration, view logs, scale, and attach add-ons.

Here’s some recommended reading. The first, an article, will give you a firmer understanding of the basics. The second is a pointer to the main Python category here on Dev Center:

• Read How Heroku Works for a technical overview of the concepts you’ll encounter while writing, configuring, deploying and running applications.
• Read Deploying Python and Django Apps on Heroku to understand how to take an existing Python or Django app and deploy it to Heroku.
• Visit the Python category to learn more about developing and deploying Python applications.
• Learn more about the Heroku developer experience and CI/CD features in the Heroku Enterprise Developer Learning Journey.