Kundan Singh

The lines that the user needs to enter or customize will be highlighed in this tutorial! The rest should mostly be copy-and-pastable.

Flask is a micro-framework written in Python and based on the Werkzeug and Jinja2 template engine for developing web applications. It is intended for developing web apps quickly.

You need to have Apache already installed and running on your VPS. If this is not the case, follow Step One of our article on installing a LAMP stack on Ubuntu.

WSGI (Web Server Gateway Interface) is an interface between web servers and web apps for python. Mod_wsgi is an Apache HTTP server mod that enables Apache to serve Flask applications.

Open terminal and type the following command to install mod_wsgi:

To enable mod_wsgi, run the following command:

In this step, we will create a flask app. We will place our app in the /var/www directory.

Use the following command to move to the /var/www directory:

Create the application directory structure using mkdir as shown. Replace "FlaskApp" with the name you would like to give your application. Create the initial directory FlaskApp by giving following command:

Move inside this directory using the following command:

Create another directory FlaskApp by giving following command:

Then, move inside this directory and create two subdirectories named static and templates using the following commands:

Your directory structure should now look like this:

Now, create the __init__.py file that will contain the flask application logic.

Add following logic to the file:

Save and close the file.

Setting up a virtual environment will keep the application and its dependencies isolated from the main system. Changes to it will not affect the cloud server's system configurations.

In this step, we will create a virtual environment for our flask application.

We will use pip to install virtualenv and Flask. If pip is not installed, install it on Ubuntu through apt-get.

If virtualenv is not installed, use pip to install it using following command:

Give the following command (where venv is the name you would like to give your temporary environment):

Now, install Flask in that environment by activating the virtual environment with the following command:

Give this command to install Flask inside:

Next, run the following command to test if the installation is successful and the app is running:

It should display “Running on http://localhost:5000/” or "Running on http://127.0.0.1:5000/". If you see this message, you have successfully configured the app.

To deactivate the environment, give the following command:

Issue the following command in your terminal:

NOTE: Newer versions of Ubuntu (13.10+) require a ".conf" extension for VirtualHost files -- run the following command instead:

Add the following lines of code to the file to configure the virtual host. Be sure to change the ServerName to your domain or cloud server's IP address:

Save and close the file.

Enable the virtual host with the following command:

Apache uses the .wsgi file to serve the Flask app. Move to the /var/www/FlaskApp directory and create a file named flaskapp.wsgi with following commands:

Add the following lines of code to the flaskapp.wsgi file:

Now your directory structure should look like this:

Restart Apache with the following command to apply the changes:

You may see a message similar to the following:

This message is just a warning, and you will be able to access your virtual host without any further issues. To view your application, open your browser and navigate to the domain name or IP address that you entered in your virtual host configuration.

You have successfully deployed a flask application.

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This tutorial needs a bit renowation. But … let’s try to patch it :)

Today, january 2016, you are probably interested in python 3

libapache2-mod-wsgi should be libapache2-mod-wsgi-py3

python-pip should be python3-pip

“sudo pip install virtualenv” should be “sudo pip3 install virtualenv”(there is more options for ve but some didn’t work for me)

"sudo pip install Flask " > "sudo pip3 install Flask "

Now serious stuff …

apache config between must have:

WSGIDaemonProcess user=flask group=www-data threads=5 python-path=/var/www/:/var/www///venv/lib/python3.4/site-packages

example:

ServerName mywebsite.comServerAdmin admin@mywebsite.comWSGIDaemonProcess user=flask group=www-data threads=5 python-path=/var/www/:/var/www///venv/lib/python3.4/site-packagesWSGIScriptAlias / /var/www/FlaskApp/flaskapp.wsgiOrder allow,denyAllow from allAlias /static /var/www/FlaskApp/FlaskApp/staticOrder allow,denyAllow from allErrorLog ${APACHE_LOG_DIR}/error.logLogLevel warnCustomLog ${APACHE_LOG_DIR}/access.log combined

But this will only work if you have additional 2 lines in flaskapp.wsgi:

activate_this = ‘/var/www///venv/bin/activate_this.py’exec(compile(open(activate_this,“rb”).read(),activate_this, ‘exec’), dict(file=activate_this))

There is alternative, you can put next line in apache config outside of :

#WSGIPythonPath /var/www///venv/lib/python3.4/site-packages

Above code was my day … farewell :)

for those with " ImportError: No module named flask", as said here http://flask.pocoo.org/docs/deploying/mod_wsgi/, I added the following lines to my wsgi file :activate_this = ‘/path/to/env/bin/activate_this.py’execfile(activate_this, dict(file=activate_this))

I have followed everything step by step and it works fine with the ‘Hello World’ app you use an example; but, when I upload my own application and try it in my browser, ****the page is loading indefinitely (‘waiting for host…’) ****so I do not get any errors to help me debug. Any idea what this could be??

Thanks for this amazing article!

No point of installing virtualenv if you do this:

That command installs packages globally.

I’m not able to use the packages installed in my virtualenv while running my web application.The error says “ImportError: No module named …”However, if I directly run the python file in /var/www/, it runs perfectly.

but how to create many flask application running at the same time ?

How can you tell Apache to run this app. using the app.'s virtualenv? Because I have the impression that the setup described here uses the global python installation!

CSS is loaded. Homepage and other static pages are displayed in “sugar coated mode”, which means following: Links and pictures are displayed, but content of the page is 404. That is done via decorator (in init.py)

@app.errorhandler(404)def page_not_found(error):return flask.render_template(‘404.html’), 404

Now, the 404.html inherits from base.html basic html tags and CSS.

In other module, I have following code:

class Main(flask.views.MethodView):def get(self, page=“index”):page+= “.html”if os.path.isfile(“templates/” + page):return flask.render_template(page)else:flask.abort(404)

I have checked whether the paths are correct via Python interactive mode and they are fine.Everything was working on flask development server. Have any idea where is the problem.

Thanks

Hi Kamal,

It works!This is the default web page for this server.The web server software is running but no content has been added, yet.

What step should I search for the problem at?

@garethprice: Disable Apache’s default virtualhost:

sudo a2dissite default

Edit the virtualhost you created and set ServerName to e.g. ServerName flaskapp.dev and restart Apache.

sudo service apache2 restart

Edit /etc/hosts on your computer and add this line to the bottom:

1.2.3.4 flaskapp.dev

Where 1.2.3.4 is your droplet’s IP address. Save it and point your browser to http://flaskapp.dev - it should load your flask app properly.