deploy-to-heroku.md

Deploying your app to Heroku - a step by step guide

Up until now, we have been working on our app and running it locally on our laptops. Whilst this is useful for testing out our app during development, it's no good if our friends want to see what we've done in this course!

In order for our friends to see the app, we need to upload (deploy) our code to Heroku, a cloud-based platform which will assign a publicly accessible URL to our app that can then be visited!

Without further ado, let's go through how you can deploy your first app to Heroku!

0. Before you start to deploy your app, there are some chores we need to do first:

   • Make a Procfile in the root folder of your application. This file contains the Command Prompt/Terminal command telling Heroku exactly how to start/run your application. It normally contains only the following line:

   web: python app.py
   

   Replace app.py with the actual name of your file containing your Flask code if you named it something different. In case you're curious: the web: part before the command basically tells Heroku to run your Python code as a web application.

   • Make a file named requirements.txt in the root folder of your application. This file lists all the external libraries (such as Flask and tweepy) required by your application, so that Heroku knows exactly the required libraries to install before trying to run your application. In this file, type in the libraries your application require line by line, which may look something like the following:

   flask
   requests
   tweepy
   

   • In app.py (or whatever you named your main file containing the Flask code), add the following line to the top of your Flask code:

   import os

   For the curious: the os module is imported so that we can access environment variables set by Heroku, which includes the port it has assigned to run your application on.

   Next (usually near the bottom of your Flask code), replace

   app.run(debug=True)

   with the following:

   if 'PORT' in os.environ:
        app.run(host='0.0.0.0', port=int(os.environ['PORT']))
   else:
        app.run(debug=True)

   Again, for the curious: this piece of conditional logic checks whether you are running your application on Heroku (in which case, the PORT environment variable would exist), or if you are running your application locally. The host=0.0.0.0 bit instructs your Flask application to listen on all web address. This is important to ensure the application runs on Heroku since we don't know which host Heroku will decide to host the application on.

1. If you haven't already, go make a Heroku account at https://www.heroku.com

2. Once you have made a Heroku account, upon logging in, you will be taken to a dashboard, which looks something like the following:

3. To deploy the app, we need to make one first on Heroku, so do that by clicking New > Create New app (button at top right of the dashboard)

4. Type in the name of your application, and change the Runtime Selection to "Europe" - this is so that the application loads faster as we are geographically closer to Europe than the United States. Finally, click "Create App".

5. After clicking "Create App", you should be greeted with the following screen:

6. Under "Deployment Method", change it to "GitHub". A "Connect to GitHub" section should now appear.

7. Under the "Connect to GitHub" section that just appeared, search for the GitHub repository corresponding to your project, then click "Connect" to link the relevant repository (appeared as a result of the search) to the Heroku application you've just created.

8. To deploy your project, click "Deploy Branch" under "Manual deploy".

9. (Optional) You may have just noticed that a section named "Automatic deploys" has appeared in addition to the "Manual deploy" section once you have connected your GitHub repository properly. To save you having to come back to this page in the future and click "Deploy Branch" each time you pushed something new to your repository, if you click "Enable Automatic Deploys", then Heroku will do so automatically.

Congratulations! You have now successfully deployed your application to Heroku!