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Deploy Flask App on VPS

Flask Deployment

In this article, we will deploy Flask Application onto a Virtual Private Server (VPS) using Apache Webserver Software and mod_wsgi WSGI.

What is VPS?

VPS, which stands for Virtual Private Server, is a virtual machine sold as a service by various hosting companies. You can think of it similar to laptop CPU hardware but in the raw form, i.e., without the Screen, keyboard, etc.

Various companies like Google, Amazon provide Cloud server services (GCP, AWS, etc.). As a part of the service, you can lend various servers situated in different parts of the world. They charge you based on different standards like the hours used, CPU utilization, etc.

Using a Cloud server gives you several advantages like:

  • Servers running 24 hrs – With Cloud Servers, your application deployed on them will be running 24hrs. In the case of the localhost(your laptop), you need to keep it running for 24 hrs which is not practical.
  • Scalability – In case your storage is full, you can scale out your services(Storage, RAM, etc.) quickly in the cloud.
  • More Secure – Since all the hardware is present in the Cloud center, It is more secure.
  • Accessibility – You can access your Cloud server from any laptop or computer.

In this tutorial, We will be using the AWS – Amazon Web Services for deployment purpose. You can go with any of the VPS providers.


Software needed to run an application on the internet

Now, a Flask Application, deployed onto a VPS need to perform the following:

  • Host Static Files like the HTML/ CSS/ JS
  • Handle Http requests
  • Recover from Crashes
  • Scale-up when required

To perform all these tasks, we require different the following softwares:

  1. A Web server software – Apache, Nginx, etc
  2. A Web Server Gateway Interface (WSGI) application server – Mod_WSGI, Gunicorn, etc
  3. Your Actual Web Application – Written using Flask, Django, etc

Here a web server software like Apache is required to handle the domain logic and also to accept the HTTP requests. The appropriate requests are then sent to the main web Application(Flask) via the WSGI application server (like mod_wsgi, Gunicorn, etc)

The WSGI application server provides the Gateway interface between the Apache software and the Flask application. WSGI is for the frameworks written in python (Django/Flask)

The primary use of WSGI is to convert the requests into a python readable format and send it to the application code (written in Flask-python), which then performs the necessary functions and returns the response Webpage.

Therefore, WSGI works as the gateway between the Apache and the Flask application.

Let us look at them individually

What is Web Server Software?

Web Server software’s primary role is to host websites on the internet. It acts as a middleman between the server and the client machines.

These software applications handle the client requests and then return the physical files(templates/data) present on the server and display them out to the clients.

Examples of Web Server Software are Apache, NGINX etc.

In this article, we will use the good old Apache server, which hosts almost 47% of the web applications on the internet

What is mod_wsgi WSGI Application Server?

Mod_wsgi is an Apache HTTP Server module that provides a WSGI compliant interface for hosting Python-based web applications under Apache. it supports Python versions 2 and 3.

It acts as an interface between Apache software and our Flask application situated on the Cloud server.

Deploying a Flask Project on a VPS

The first step is to select a server from a VPS provider. Any VPS providing companies will have several servers running on different OS systems, as shown

AWS Servers
AWS Servers

After selecting the required one, you will have to go through some steps to set up and launch the server.

Do note that you have the HTTP port (80) enabled on your Cloud server. Port 80 is the port that the Web server software(Apache, etc.) “listens to” or receives requests from a Web client.

AWS HTTP Port
Aws HTTP Post

Once the server is set-up, you will get the IP address or the Public DNS of the server, which will be later required to connect to the cloud server.

Aws
Aws

1. Connecting to the Cloud Server from the Local Computer

We use the ssh command to connect to the server. To connect to the Cloud server from our local computer, run the following commands:

  • Using Mac or Linux:

In the shell, simply run the code:

ssh username@<server_IP>

In case you are using an Ubuntu server, the username is ubuntu.

  • Using Windows

For windows, we use a software called PuTTY, which you can download from directly from the internet. Once downloaded, enter the cloud_IP in there and hit open.

PuTTY
PuTTY

My cloud_IP/Public DNS which I will be using to access my server is:

Public DNS
Public DNS

For AWS, we need to use an additional private security key as well. Hence depending on the VPS provider, you might also need to add the security_key

Once it is done, you will be logged into the cloud server OS.

Ubuntu
Ubuntu

2. Installing necessary packages

Once the server is connected, it will be similar to the new ubuntu computer. We first need to install all the important packages into it.

So run the following commands:

Installing Upgrades

sudo apt update
sudo apt upgrade

Always update the system, after starting the server.

Installing apache2 and mod_wsgi on the server

Now let’s first Install Apache2 and the mod_wsgi packages on the system

sudo apt install apache2
sudo apt install libapache2-mod-wsgi

To check whether Apache2 is working or not, go to the Public DNS/IP address of your Cloud server. You will see the Apache Default Page.

Installing python3-pip

Now Install python3 and pip on to the system using:

sudo apt install python-pip

Installing Flask and its extensions

Now install Flask Framework and all other required Flask Extensions like Flask_SQLAlchemy, Flask_login, Flask_wtf, etc

sudo pip install flask
sudo pip install flask_sqlalchemy
....
....

Just install whatever Flask Extensions you require for your Flask Project.

3. Transferring the Flask project from the Local Machine to the Cloud Server

You can create a new directory and code the entire Flask app in there itself using the nano text editor.

mkdir flask_project
cd flask_project

A better option is to code the project on your local machine and then transfer the flask_project folder to the cloud server.

To transfer the file, we use the code

scp -i <path/to/secret_key> -r <path/to/file> ubuntu@<public_DNS>:<path/to/destination>
Transfer Files
Transfer Files

In AWS, we also need to insert a security key. If your VPS provider does not have any security_key, then remove the key_path from the command

Link the Flask Application Project Directory flask_project present in the Home Directory, with Apache’s Configurations (present in the /var/www/html directory). We do it using the code:

sudo ln -sT ~/flask_project /var/www/html/flask_project

4. Coding the Flask Application

Inside the Flask_project folder, you should be having all the Flask files – app.py, models.py, Templates, etc.

Let us code a simple Flask Application, so in the flask_project directory, create a file app.py

sudo nano app.py

and add the code:

from flask import Flask

app = Flask(__name__)

@app.route('/blogs')
def blogs():
  return 'Welcome to The Blog App'

@app.route('/blog/<int:id>')
def blog(id):
  return "The Blog id is {}".format(id)

if __name__ == '__main__':
  app.run()

After that, we now have to create a WSGI file. For that create a .wsgi file with the same name as the main Flask Application File. In my case, it is app.wsgi

using nano app.wsgi, add the code:

#flaskapp.wsgi
import sys
sys.path.insert(0, '/var/www/html/flask_project')

from app import app as application

Great!! Now we need to enable the mod_wsgi for Apache to interact with the Flask App.

For that go to /etc/apache2/sites-enabled/:

cd /etc/apache2/sites-enabled/

Open the conf file 000-default.conf using nano Text editor and below DocumentRoot /var/www/html line, add the code:

WSGIDaemonProcess flask_project threads=5
WSGIScriptAlias / /var/www/html/flask_project/app.wsgi

<Directory flask_project>
    WSGIProcessGroup flask_project
    WSGIApplicationGroup %{GLOBAL}
    Order deny,allow
    Allow from all
</Directory>
Conf File
Conf File

Running the Flask Application

That’s it now restart the apache server:

sudo service apache2 restart

And go to the public DNS, the website will be up and running !!

Blogss
Blogss

Similarly to the other URL

Blogs1
Blogs1

Perfect!

Conclusion

Your Flask application is up and running on the cloud server. Do Try to Run your own Flask Application on the Cloud Server and let us know what you think. See you guys next time 🙂