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How To Serve Django Applications with uWSGI and Nginx on CentOS 7

PostedMarch 13, 2015 38.8k views Deployment Django Nginx Python Frameworks Python CentOS

Introduction

Django is a powerful web framework that can help you get your Python application or website off the ground. Django includes a simplified development server for testing your code locally, but for anything even slightly production related, a more secure and powerful web server is required.

In this guide, we will demonstrate how to install and configure some components on CentOS 7 to support and serve Django applications. We will configure the uWSGI application container server to interface with our applications. We will then set up Nginx to reverse proxy to uWSGI, giving us access to its security and performance features to serve our apps.

Prerequisites and Goals

In order to complete this guide, you should have a fresh CentOS 7 server instance with a non-root user with sudo privileges configured. You can learn how to set this up by running through our initial server setup guide.

We will be installing Django within two different virtual environments. This will allow your projects and their requirements to be handled separately. We will be creating two sample projects so that we can run through the steps in a multi-project environment.

Once we have our applications, we will install and configure the uWSGI application server. This will serve as an interface to our applications which will translate client requests using HTTP to Python calls that our application can process. We will then set up Nginx in front of uWSGI to take advantage of its high performance connection handling mechanisms and its easy-to-implement security features.

Let's get started.

Install and Configure VirtualEnv and VirtualEnvWrapper

We will be installing our Django projects in their own virtual environments to isolate the requirements for each. To do this, we will be installing virtualenv, which can create Python virtual environments, and virtualenvwrapper, which adds some usability improvements to the virtualenv work flow.

We will be installing both of these components using pip, the Python package manager. To get pip, we first need to enable the EPEL repository. We can do this easily by typing:

sudo yum install epel-release

Once EPEL is enabled, we can install pip by typing:

sudo yum install python-pip

Now that you have pip installed, we can install virtualenv and virtualenvwrapper globally by typing:

sudo pip install virtualenv virtualenvwrapper

With these components installed, we can now configure our shell with the information it needs to work with the virtualenvwrapper script. Our virtual environments will all be placed within a directory in our home folder called Env for easy access. This is configured through an environmental variable called WORKON_HOME. We can add this to our shell initialization script and can source the virtual environment wrapper script.

To add the appropriate lines to your shell initialization script, you need to run the following commands:

echo "export WORKON_HOME=~/Env" >> ~/.bashrc
echo "source /usr/bin/virtualenvwrapper.sh" >> ~/.bashrc

Now, source your shell initialization script so that you can use this functionality in your current session:

source ~/.bashrc

You should now have directory called Env in your home folder which will hold virtual environment information.

Create Django Projects

Now that we have our virtual environment tools, we will create two virtual environments, install Django in each, and start two projects.

Create the First Project

We can create a virtual environment easily by using some commands that the virtualenvwrapper script makes available to us.

Create your first virtual environment with the name of your first site or project by typing:

mkvirtualenv firstsite

This will create a virtual environment, install Python and pip within it, and activate the environment. Your prompt will change to indicate that you are now operating within your new virtual environment. It will look something like this: (firstsite)user@hostname:~$. The value in the parentheses is the name of your virtual environment. Any software installed through pip will now be installed into the virtual environment instead of on the global system. This allows us to isolate our packages on a per-project basis.

Our first step will be to install Django itself. We can use pip for this without sudo since we are installing this locally in our virtual environment:

pip install django

With Django installed, we can create our first sample project by typing:

cd ~
django-admin.py startproject firstsite

This will create a directory called firstsite within your home directory. Within this is a management script used to handle various aspects of the project and another directory of the same name used to house the actual project code.

Move into the first level directory so that we can begin setting up the minimum requirements for our sample project.

cd ~/firstsite

Begin by migrating the database to initialize the SQLite database that our project will use. You can set up an alternative database for your application if you wish, but this is outside of the scope of this guide:

./manage.py migrate

You should now have a database file called db.sqlite3 in your project directory. Now, we can create an administrative user by typing:

./manage.py createsuperuser

You will have to select a username, give a contact email address, and then select and confirm a password.

Next, open the settings file for the project with your text editor:

nano firstsite/settings.py

Since we will be setting up Nginx to serve our site, we need to configure a directory which will hold our site's static assets. This will allow Nginx to serve these directly, which will have a positive impact on performance. We will tell Django to place these into a directory called static in our project's base directory. Add this line to the bottom of the file to configure this behavior:

STATIC_ROOT = os.path.join(BASE_DIR, "static/")

Save and close the file when you are finished. Now, collect our site's static elements and place them within that directory by typing:

./manage.py collectstatic

You can type "yes" to confirm the action and collect the static content. There will be a new directory called static in your project directory.

With all of that out of the way, we can test our project by temporarily starting the development server. Type:

./manage.py runserver 0.0.0.0:8080

This will start up the development server on port 8080. Visit your server's domain name or IP address followed by 8080 in your browser:

http://server_domain_or_IP:8080

You should see a page that looks like this:

Django sample site

Add /admin to the end of the URL in your browser's address bar and you will be taken to the admin login page:

Django admin login

Using the administrative login credentials you selected with the createsuperuser command, log into the server. You will then have access to the administration interface:

Django admin interface

After testing this functionality out, stop the development server by typing CTRL-C in your terminal. We can now move on to our second project.

Create the Second Project

The second project will be created in exactly the same way as the first. We will abridge the explanation in this section, seeing as how you have already completed this once.

Move back to your home directory and create a second virtual environment for your new project. Install Django inside of this new environment once it is activated:

cd ~
mkvirtualenv secondsite
pip install django

The new environment will be created and changed to, leaving your previous virtual environment. This Django instance is entirely separate from the other one you configured. This allows you to manage them independently and customize as necessary.

Create the second project and move into the project directory:

django-admin.py startproject secondsite
cd ~/secondsite

Initialize the database and create an administrative user:

./manage.py migrate
./manage.py createsuperuser

Open the settings file:

nano secondsite/settings.py

Add the location for the static files, just as you did in the previous project:

STATIC_ROOT = os.path.join(BASE_DIR, "static/")

Save and close the file. Now, collect the static elements into that directory by typing:

./manage.py collectstatic

Finally, fire up the development server to test out the site:

./manage.py runserver 0.0.0.0:8080

You should check the regular site at:

http://server_domain_or_IP:8080

Also log into the admin site:

http://server_domain_or_IP:8080/admin

When you've confirmed that everything is working as expected, type CTRL-C in your terminal to stop the development server.

Backing Out of the Virtual Environment

Since we are now done with the Django portion of the guide, we can deactivate our second virtual environment:

deactivate

If you need to work on either of your Django sites again, you should reactivate their respective environments. You can do that by using the workon command:

workon firstsite

Or:

workon secondsite

Again, deactivate when you are finished working on your sites:

deactivate

Setting up the uWSGI Application Server

Now that we have two Django projects set up and ready to go, we can configure uWSGI. uWSGI is an application server that can communicate with applications over a standard interface called WSGI. To learn more about this, read this section of our guide on setting up uWSGI and Nginx on Ubuntu 14.04.

Installing uWSGI

Unlike the guide linked above, in this tutorial, we'll be installing uWSGI globally. This will create less friction in handling multiple Django projects. Before we can install uWSGI, we need the Python development files that the software relies on. We also need a compiler. We can get both of these using yum:

sudo yum install python-devel gcc

Now that the development files are available, we can install uWSGI globally through pip by typing:

sudo pip install uwsgi

We can quickly test this application server by passing it the information for one of our sites. For instance, we can tell it to serve our first project by typing:

uwsgi --http :8080 --home /home/user/Env/firstsite --chdir /home/user/firstsite -w firstsite.wsgi

Here, we've told uWSGI to use our virtual environment located in our ~/Env directory, to change to our project's directory, and to use the wsgi.py file stored within our inner firstsite directory to serve the file. For our demonstration, we told it to serve HTTP on port 8080. If you go to server's domain name or IP address in your browser, followed by :8080, you will see your site again (the static elements in the /admin interface won't work yet). When you are finished testing out this functionality, type CTRL-C in the terminal.

Creating Configuration Files

Running uWSGI from the command line is useful for testing, but isn't particularly helpful for an actual deployment. Instead, we will run uWSGI in "Emperor mode", which allows a master process to manage separate applications automatically given a set of configuration files.

Create a directory that will hold your configuration files. Since this is a global process, we will create a directory called /etc/uwsgi/sites to store our configuration files. Move into the directory after you create it:

sudo mkdir -p /etc/uwsgi/sites
cd /etc/uwsgi/sites

In this directory, we will place our configuration files. We need a configuration file for each of the projects we are serving. The uWSGI process can take configuration files in a variety of formats, but we will use .ini files due to their simplicity.

Create a file for your first project and open it in your text editor:

sudo nano firstsite.ini

Inside, we must begin with the [uwsgi] section header. All of our information will go beneath this header. We are also going to use variables to make our configuration file more reusable. After the header, set a variable called project with the name of your first project. Set another variable with your normal username that owns the project files. Add a variable called base that uses your username to establish the path to your user's home directory:

[uwsgi]
project = firstsite
username = user
base = /home/%(username)

Next, we need to configure uWSGI so that it handles our project correctly. We need to change into the root project directory by setting the chdir option. We can combine the home directory and project name setting that we set earlier by using the %(variable_name) syntax. This will be replaced by the value of the variable when the config is read.

In a similar way, we will indicate the virtual environment for our project. By setting the module, we can indicate exactly how to interface with our project (by importing the "application" callable from the wsgi.py file within our project directory). The configuration of these items will look like this:

[uwsgi]
project = firstsite
username = user
base = /home/%(username)

chdir = %(base)/%(project)
home = %(base)/Env/%(project)
module = %(project).wsgi:application

We want to create a master process with 5 workers. We can do this by adding this:

[uwsgi]
project = firstsite
username = user
base = /home/%(username)

chdir = %(base)/%(project)
home = %(base)/Env/%(project)
module = %(project).wsgi:application

master = true
processes = 5

Next we need to specify how uWSGI should listen for connections. In our test of uWSGI, we used HTTP and a network port. However, since we are going to be using Nginx as a reverse proxy, we have better options.

Instead of using a network port, since all of the components are operating on a single server, we can use a Unix socket. This is more secure and offers better performance. This socket will not use HTTP, but instead will implement uWSGI's uwsgi protocol, which is a fast binary protocol designed for communicating with other servers. Nginx can natively proxy using the uwsgi protocol, so this is our best choice.

We need to set the user who will run the process. We will also modify the permissions and ownership of the socket because we will be giving the web server write access. The socket itself will be placed within the /run/uwsgi directory (we'll create this directory in a bit) where both uWSGI and Nginx can reach it. We'll set the vacuum option so that the socket file will be automatically cleaned up when the service is stopped:

[uwsgi]
project = firstsite
username = user
base = /home/%(username)

chdir = %(base)/%(project)
home = %(base)/Env/%(project)
module = %(project).wsgi:application

master = true
processes = 5

uid = %(username)
socket = /run/uwsgi/%(project).sock
chown-socket = %(username):nginx
chmod-socket = 660
vacuum = true

With this, our first project's uWSGI configuration is complete. Save and close the file.

The advantage of setting up the file using variables is that it makes it incredibly simple to reuse. Copy your first project's configuration file to use as a base for your second configuration file:

sudo cp /etc/uwsgi/sites/firstsite.ini /etc/uwsgi/sites/secondsite.ini

Open the second configuration file with your text editor:

sudo nano /etc/uwsgi/sites/secondsite.ini

We only need to change a single value in this file in order to make it work for our second project. Modify the project variable with the name you've used for your second project:

[uwsgi]
project = firstsite
username = user
base = /home/%(username)

chdir = %(base)/%(project)
home = %(base)/Env/%(project)
module = %(project).wsgi:application

master = true
processes = 5

uid = %(username)
socket = /run/uwsgi/%(project).sock
chown-socket = %(username):nginx
chmod-socket = 660
vacuum = true

Save and close the file when you are finished. Your second project should be ready to go now.

Create a Systemd Unit File for uWSGI

We now have the configuration files we need to serve our Django projects, but we still haven't automated the process. Next, we'll create a Systemd unit file to automatically start uWSGI at boot.

We will create the unit file in the /etc/systemd/system directory where user-created unit files are kept. We will call our file uwsgi.service:

sudo nano /etc/systemd/system/uwsgi.service

Start with the [Unit] section, which is used to specify metadata. We'll simply put a description of our service here:

[Unit]
Description=uWSGI Emperor service

Next, we'll open up the [Service] section. We'll use the ExecStartPre directive to set up the pieces we need to run our server. This will make sure the /run/uwsgi directory is created and that our normal user owns it with the Nginx group as the group owner. Both mkdir with the -p flag and the chown command return successfully even if they already exist. This is what we want.

For the actual start command, specified by the ExecStart directive, we will point to the uwsgi executable. We will tell it to run in "Emperor mode", allowing it to manage multiple applications using the files it finds in /etc/uwsgi/sites. We will also add the pieces needed for Systemd to correctly manage the process. These are taken from the uWSGI documentation here:

[Unit]
Description=uWSGI Emperor service

[Service]
ExecStartPre=/usr/bin/bash -c 'mkdir -p /run/uwsgi; chown user:nginx /run/uwsgi'
ExecStart=/usr/bin/uwsgi --emperor /etc/uwsgi/sites
Restart=always
KillSignal=SIGQUIT
Type=notify
NotifyAccess=all

Now, all we need to do is add the [Install] section. This allows us to specify when the service should be automatically started. We will tie our service to the multi-user system state. Whenever the system is set up for multiple users (the normal operating condition), our service will be activated:

[Unit]
Description=uWSGI Emperor service

[Service]
ExecStartPre=/usr/bin/bash -c 'mkdir -p /run/uwsgi; chown user:nginx /run/uwsgi'
ExecStart=/usr/bin/uwsgi --emperor /etc/uwsgi/sites
Restart=always
KillSignal=SIGQUIT
Type=notify
NotifyAccess=all

[Install]
WantedBy=multi-user.target

When you are finished with this, save and close the file.

We will be unable to start the service successfully at this point because it relies on the nginx user being available. We will have to wait to start the uWSGI service until after Nginx is installed.

Install and Configure Nginx as a Reverse Proxy

With uWSGI configured and ready to go, we can now install and configure Nginx as our reverse proxy. This can be downloaded and installed using yum:

sudo yum install nginx

Once Nginx is installed, we can go ahead and edit the main configuration file:

sudo nano /etc/nginx/nginx.conf

Within this file, next to the existing server block, we will create an additional server block for each of our sites:

http {

    . . .

    include /etc/nginx/conf.d/*.conf;

    server {
    }

    server {
    }

    server {
        listen 80 default_server;
        server_name localhost;

        . . .

The blocks we created will hold the configuration for our uWSGI sites. We'll cover the directives that we need in the first server block now.

First, we need to tell the server block which port number and domain name that it should respond to. We'll assume that you have a domain name for each of your sites:

server {
    listen 80;
    server_name firstsite.com www.firstsite.com;
}

Next, we'll tell Nginx that we don't need to worry about a missing favicon. We will then specify the directory where our first site's static assets were collected for when these files are requested. Nginx can hand them straight to the client from that directory:

server {
    listen 80;
    server_name firstsite.com www.firstsite.com;

    location = favicon.ico { access_log off; log_not_found off; }
    location /static/ {
        root /home/user/firstsite;
    }
}

Next, we create a catch-all location block that will pass all additional queries straight to uWSGI. We will include the uwsgi parameters found in the /etc/nginx/uwsgi_params file and pass the traffic to the socket that the uWSGI server sets up:

server {
    listen 80;
    server_name firstsite.com www.firstsite.com;

    location = favicon.ico { access_log off; log_not_found off; }
    location /static/ {
        root /home/user/firstsite;
    }

    location / {
        include uwsgi_params;
        uwsgi_pass unix:/run/uwsgi/firstsite.sock;
    }
}

With that, our first server block is complete.

The second server block for our other site will be almost the same. You can copy and paste the server block we just created to get started. You will need to modify the domain name that the site should respond to, the location of the site's static files, and the site's socket file:

server {
    listen 80;
    server_name secondsite.com www.secondsite.com;

    location = favicon.ico { access_log off; log_not_found off; }
    location /static/ {
        root /home/user/secondsite;
    }

    location / {
        include uwsgi_params;
        uwsgi_pass unix:/run/uwsgi/secondsite.sock;
    }
}

When you are finished with this step, save and close the file.

Check the syntax of the Nginx file to make sure you don't have any mistakes:

sudo nginx -t

If no errors are reported, our file is in good condition.

We have one additional task we have to complete to make our sites work correctly. Since Nginx is handling the static files directly, it needs access to the appropriate directories. We need to give it executable permissions for our home directory, which is the only permission bit it is lacking.

The safest way to do this is to add the Nginx user to our own user group. We can then add the executable permission to the group owners of our home directory, giving just enough access for Nginx to serve the files:

sudo usermod -a -G user nginx
chmod 710 /home/user

Now, we can start the Nginx server and the uWSGI process:

sudo systemctl start nginx
sudo systemctl start uwsgi

You should now be able to reach your two projects by going to their respective domain names. Both the public and administrative interfaces should work as expected.

If this goes well, you can enable both of the services to start automatically at boot by typing:

sudo systemctl enable nginx
sudo systemctl enable uwsgi

Conclusion

In this guide, we've set up two Django projects, each in their own virtual environments. We've configured uWSGI to serve each project independently using the virtual environment configured for each. Afterwards, we set up Nginx to act as a reverse proxy to handle client connections and serve the correct project depending on the client request.

Django makes creating projects and applications simple by providing many of the common pieces, allowing you to focus on the unique elements. By leveraging the general tool chain described in this article, you can easily serve the applications you create from a single server.

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