Deploy Python web application on Ubuntu server

Components used for this article:

Suppose that we already installed an Ubuntu image on a Linode plan.

Update packages

sudo apt-get update && apt-get upgrade

DNS resolution

Add a A record for the domain name of the application.

Nginx

Install Nginx

sudo apt-get install nginx

Configure Ngnix

Create a cofiguration file under /etc/nginx/conf.d/ with name [app_name].conf.

sudo nano /etc/nginx/conf.d/[app_name].conf

Configure without https

Template of /etc/nginx/conf.d/[app_name].conf:

upstream app_server_wsgiapp {
    server localhost:8000 fail_timeout=0;
}

server {
    listen 80;
    # make sure to change the next line to your own domain name!
    server_name appname.example.com;
    access_log /var/log/nginx/appname.access.log;
    error_log /var/log/nginx/appname.error.log info;
    keepalive_timeout 5;

    # nginx serve up static files and never send to the WSGI server
    location /static {
        autoindex on;
        alias /home/username/appname/static;
    }

    location / {
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header Host $http_host;
            proxy_redirect off;
            if (!-f $request_filename) {
                proxy_pass http://app_server_wsgiapp;
                break;
            }
    }

    # this section allows Nginx to reverse proxy for websockets
    location /socket.io {
        proxy_pass http://app_server_wsgiapp/socket.io;
        proxy_redirect off;
        proxy_buffering off;

        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;

        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "Upgrade";
    }
}

Configure with https

(to add)

Restart nginx

Delete default website file:

sudo rm /etc/nginx/sites-enabled/default

Apply new configuration:

sudo service nginx restart

PostgreSQL

Install PostgreSQL

sudo apt-get install postgresql libpq-dev postgresql-client-common postgresql-client

then create database and new user

# switch to postgres user
sudo su - postgres

# create database
createdb dbname

# create a non-root database user and set password
createuser --superuser username
psql
ALTER USER username WITH PASSWORD 'password'


(For me, it seems that the last line would take effect, but we can change the password later.)

Press CTRL-D to quit psql, and CTRL-D again to quit postgres user.

Now database dbname is created and user username is able to access the database.

# Connect to database
psql dbname

# Show tables
dt

Change password of current user:

password

Redis

Install Redis

sudo apt-get install redis-server

Test using redis-cli.

Python application

Install pip, virtualenv

sudo apt-get install python3-pip
sudo apt-get install python3.4-venv
sudo python3 -m pip install virtualenv virtualenvwrapper

Note: python3.4-venv not python3-venv

Make virtualenv

# set an environment variable to where you want your virtual environment
export VENV=~/env
# create the virtual environment
python3 -m venv $VENV

Upgrade packages in virtualenv

$VENV/bin/pip install --upgrade pip setuptools

“Why use $VENV/bin/pip instead of source bin/activate, then pip?” From Pyramid docs:

$VENV/bin/pip clearly specifies that pip is run from within the virtual environment and not at the system level.

activate drops turds into the user’s shell environment, leaving them vulnerable to executing commands in the wrong context. deactivate might not correctly restore previous shell environment variables.

Although using source bin/activate, then pip, requires fewer key strokes to issue commands once invoked, there are other things to consider. Michael F. Lamb (datagrok) presents a summary in Virtualenv’s bin/activate is Doing It Wrong.

Ultimately we prefer to keep things clear and simple, so we use $VENV/bin/pip.

Pyramid

Install Pyramid

# install pyramid
$VENV/bin/pip install pyramid
# or for a specific released version
$VENV/bin/pip install "pyramid==1.7.3"

Demo app

We create a demo app using scaffold provided by Pyramid.

$VENV/bin/pcreate -s starter demo
cd demo
$VENV/bin/pip install -e .

WSGI server

Install Gunicorn

$VENV/bin/pip install gunicorn

Run the demo app:

cd ~/demo
$VENV/bin/gunicorn --paste development.ini -b :8000

8000 is the port gunicorn listens from the nginx reverse proxy, which we set in /etc/nginx/conf.d/demo.conf.

Open a browser and visit the URL and the app should be running.

Start gunicorn server with supervisor

Install supervisor

sudo apt-get install supervisor

Configure supervisor. Create a file /etc/supervisor/conf.d/[app_name].conf, and add lines: (e.g., for demo app, the file name should be demo.conf)

[program:demo] 
environment=DEBUG=False
command=/home/[username]/venv/bin/gunicorn --paste [path/to/app/]development.ini -b :8000 --chdir [path/to/app]
directory=/home/[username]/demo 
user=[username]
autostart=true 
autorestart=true
redirect_stderr=True

Start supervisor service:

sudo service supervisor start

Visit the URL and the app should be running.

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