Setting up flask in DreamHost for web app deployment

Step by step guidance for setting up the flask on DreamHost for web app deployment.

These steps are valid for both Shared Website Hosting and Virtual Private Server.

Enable Passenger for your domain

DreamHost uses Passenger to simplify the deployment of Flask web apps. The process of enabling Passenger for a site/domain/subdomain can be found in the DreamHost documentation https://help.dreamhost.com/hc/en-us/articles/216385637-How-do-I-enable-Passenger-on-my-domain-. The easiest way might be to select Passenger in the process of creating a domain/subdomain instead of changing it after the creation of the domain.

Connection of SSH to the server

There are a large range of SSH clients that you can choose to connect to the server, on systems including MacOS X, Unix/Linux, Windows, Chrome, IOS (iphone), and Android. Here is a quick list in the DreamHost documentation https://help.dreamhost.com/hc/en-us/articles/215360828-SSH-client-software.

There are two ways to connect the SSH to the server:

[server]$ ssh username@example.com

or

[server]$ ssh username@server.dreamhost.com

followed by inputting the password upon pressing "Enter".

The username and password can be easily found in the DreamHost Panel - Websites - FTP Users & Files.

The server in the second option is your host name, like vps*****.dreamhostps.com. More information can be found in the DreamHost documentation https://help.dreamhost.com/hc/en-us/articles/216041267-SSH-overview. To make it easier, we recommend using the first option whenever possible.

Use existing python (e.g., python3.8)

• Before having to install a custom version of python, you may want to check whether the system already has one that you can use. To check all the available versions, type [server]$ python followed by two tabs. This may give you a few available versions. If you want to use one of it (e.g., python3.8), then type [server]$ which python3.8, which will give you the location of this python (e.g., /usr/bin/python3.8). To use it, create an environment called venv_new based on this python by [server]$ virtualenv venv_new -p /usr/bin/python3.8 (assuming the virtualenv is installed already. If not, simply do [server]$ python3 -m pip install --upgrade pip and pip3 install virtualenv to install it).

Python3 installation

• If you want to install your own version of python, run below command one by one. Below example installs Python 3.9.2. You can change this based on your own needs.

[server]$ cd ~
[server]$ mkdir py3_tmp
[server]$ cd py3_tmp
[server]$ wget https://www.python.org/ftp/python/3.9.2/Python-3.9.2.tgz
[server]$ tar zxvf Python-3.9.2.tgz 
[server]$ cd Python-3.9.2 
[server]$ ./configure --prefix=$HOME/opt/python-3.9.2
[server]$ make
[server]$ make install
[server]$ echo 'export PATH=$HOME/opt/python-3.9.2/bin:$PATH' >> ~/.bash_profile
[server]$ . ~/.bash_profile

The last two commands set this version of Python as the default for the user, and then reload the file to activate it.

• Now it is the time to check if the wanted version of Python3 as well as the pip3 are successfully installed. To do that, run the commands:

[server]$ which python3
/home/username/opt/python-3.9.2/bin/python3

[server]$ python3 --version
Python 3.9.2

[server]$ pip3 --version
pip 21.2.4 from /home/username/opt/python-3.9.2/lib/python3.9/site-packages/pip (python 3.9)    

• Now we can delete the temporary folder py3_tmp using the command below:

[server]$ cd ~
[server]$ rm -r py3_tmp

Please also check the DreamHost documentation for more information: https://help.dreamhost.com/hc/en-us/articles/115000702772-Installing-a-custom-version-of-Python-3

Install a virtual environment

To install Flask and any other libraries, a virtual environment may be installed first so that these packages will be isolated from the rest of the applications on the server.

• To do that, we use pip3 that we just installed together with the Python3 in above steps. Before that, pip3 may be upgraded to the newest version first:

[server]$ python3 -m pip install --upgrade pip

• Once upgraded, install virtualenv using pip3:

[server]$ pip3 install virtualenv

• then check it:

[server]$ which virtualenv

• Create the venv itself (change the username to your actual username):

virtualenv -p /home/username/opt/python-3.9.2/bin/python3 venv

• Activate your venv:

[server]$ source venv/bin/activate

Now the name of the current virtual environment appears to the left of the prompt, for example:

(venv) [server]$ 

• To verify the installation again:

(venv) [server]$ python -V
Python 3.9.2

For more information, check the DreamHost documentation at https://help.dreamhost.com/hc/en-us/articles/115000695551-Installing-and-using-virtualenv-with-Python-3.

Install Flask and other Python libraries

• Make sure the pip3 is upgraded to the newest version, and the correct virtual environment (in this case, the venv) is activated:

[server]$ python3 -m pip install --upgrade pip
[server]$ source venv/bin/activate

• Now you can install flask into the virtual environment:

(venv) [server]$ pip install Flask

or other libraries (e.g., numpy and pandas):

(venv) [server]$ pip install numpy
(venv) [server]$ pip install pandas

Configure Passenger

• Create a Passenger configuration file (this should be in your home directory in the example.com):

(venv) [server]$ nano passenger_wsgi.py

• Then enter the following contents in to the passenger_wsgi.py file:

import sys, os
INTERP = os.path.expanduser("/home/username/example.com/venv/bin/python3") ### In terminal, with the environment `venv` activated, type "which python3". The result would be used here.
if sys.executable != INTERP:
    os.execl(INTERP, INTERP, *sys.argv)
sys.path.append(os.getcwd())
sys.path.append('~/example.com/app') # This is the address of your `app` folder, as shown below.
from app.app import app as application

if __name__ == '__main__':
    application.run(debug=False)

• Save and close the file, and make it executable:

(venv) [server]$ chmod +x passenger_wsgi.py

• Because every change in the website requires a restart to reflect the change, here we create a folder tmp with a file restart.txt as the restart button:

(venv) [server]$ cd ~
(venv) [server]$ mkdir tmp
(venv) [server]$ touch tmp/restart.txt

Create the Flask app

• Create a folder called app in your domain folder (make sure to navigate to the correct directory before doing so):

(venv) [server]$ cd /home/username/example.com
(venv) [server]$ mkdir app

• Create the major app file called app.py in the folder app, and add following contents (the index.html is the home page of your site, located in the folder templates):

from app import app

app = Flask(__name__)

#default page of our web-app
@app.route('/')
def home():
    return render_template('index.html')


#Starting the Flask Server 
if __name__ == '__main__':
    app.debug = True
    app.run()

• Create another file called __init__.py also in the folder app, and add the following content:

from flask import Flask

app = Flask(__name__)

from app import app

Create other related app functions and HTML pages

Above contents can very well guide you to establish a very basic Flask application on DreamHost. You can add more functions or webpages to your site based on your own needs.

References

• https://help.dreamhost.com/hc/en-us/articles/216385637-How-do-I-enable-Passenger-on-my-domain-
• https://help.dreamhost.com/hc/en-us/articles/215360828-SSH-client-software
• https://help.dreamhost.com/hc/en-us/articles/216041267-SSH-overview
• https://help.dreamhost.com/hc/en-us/articles/115000702772-Installing-a-custom-version-of-Python-3
• https://help.dreamhost.com/hc/en-us/articles/115000695551-Installing-and-using-virtualenv-with-Python-3
• https://www.brettsbeta.com/blog/2020/07/flask-on-dreamhost-shared-website-hosting/
• https://github.com/jprusik/dreamhost-flask-project-template