25 12 / 2013

This article will focus on deploying flask app starting from scratch like creating separate linux user, installating database, web server. Web server will be nginx, database will be postgres, python 2.7 middleware will be uwsgi, server ubuntu 13.10 x64. Flask app name is fido. Demo is carried out in Digital ocean.

Step 1 - Installation


Python header

root@fido:~# apt-get install -y build-essential python-dev

Install uwsgi dependencies

root@fido:~# apt-get install -y libxml2-dev libxslt1-dev

Nginx, uwsgi

root@fido:~#  apt-get install -y nginx uwsgi uwsgi-plugin-python

Start nginx

root@fido:~# service nginx start
* Starting nginx nginx                                                          [ OK ]

Postgres

root@fido:~# apt-get install -y postgresql postgresql-contrib libpq-dev

Step 2 - User

Create a new linux user fido

root@fido:~# adduser fido

Enter all the required details.

root@fido:~# ls /home
fido

Successfully new user is created.

Grant fido root privilege.

root@fido:~# /usr/sbin/visudo
# User privilege specification

root    ALL=(ALL:ALL) ALL 
fido    ALL=(ALL:ALL) ALL

Since fido is not normal user, delete fido’s home directory.

root@fido:~# rm -rf /home/fido
root@fido:~# ls /home
root@fido:~#

Create a new db user fido

root@fido:~# su - postgres
postgres@fido:~$ createuser --pwprompt
Enter name of role to add: fido
Enter password for new role:
Enter it again:
Shall the new role be a superuser? (y/n) y

--pwprompt will prompt for password. release is the password I typed (we need this to connect db from app).

Create a new database fido

postgres@fido:~$ createdb fido;
postgres@fido:~$ psql -U fido -h localhost
Password for user fido:
psql (9.1.10)
SSL connection (cipher: DHE-RSA-AES256-SHA, bits: 256)
Type "help" for help.
fido=# \d
No relations found.

Done. New database role fido and database is created. We are successfully able to login.

Step 3 - Python dependencies

Install pip

root@fido:# cd /tmp
root@fido:/tmp# wget https://bitbucket.org/pypa/setuptools/raw/bootstrap/ez_setup.py
root@fido:/tmp# python ez_setup.py install
root@fido:/tmp# easy_install pip 
# What is easy_install ? Python package manager.
# what is pip ? Python package manager.
# How to install pip ? easy_install pip. 
# Shame on python :-(
...
Installed /usr/local/lib/python2.7/dist-packages/pip-1.4.1-py2.7.egg
Processing dependencies for pip
Finished processing dependencies for pip

Install virtualenv

root@fido:/tmp# pip install virtualenv

Step 4 - Install app dependencies

Here is the sample app code. The app is just for demo. The app will be placed in /var/www/fido. Normally in production, this will be similar to git clone <url> or hg clone <url> inside directory. Make sure you aren’t sudo while cloning.

root@fido:/tmp# cd /var
root@fido:/var# mkdir www
root@fido:/var# mkdir www/fido

Change the owner of the repo to fido.

root@fido:/var# chown fido:fido www/fido
root@fido:/var# ls -la www/
total 12
drwxr-xr-x  3 root root 4096 Dec 25 03:18 .
drwxr-xr-x 14 root root 4096 Dec 25 03:18 ..
drwxr-xr-x  2 fido fido 4096 Dec 25 03:18 fido

app.py - fido application.

# /usr/bin/env python

from flask import Flask, request
from flask.ext.sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = "postgres://fido:release@localhost:5432/fido"
db = SQLAlchemy(app)


class Todo(db.Model):
    id = db.Column(db.Integer(), nullable=False, primary_key=True)
    name = db.Column(db.UnicodeText(), nullable=False)
    status = db.Column(db.Boolean(), default=False, nullable=True)


@app.route("/")
def index():
    return "Index page. Use /new create a new todo"


@app.route('/new', methods=['POST'])
def new():
    form = request.form
    name, status = form.get('name'), form.get('status') or False
    todo = Todo(name=name, status=status)
    db.session.add(todo)
    db.session.commit()
    return "Created todo: {}".format(name)


if __name__ == "__main__":
    db.create_all()
    app.run('0.0.0.0', port=3333, debug=True)

Add a wsgi file website.py

root@fido:/var/www/fido# cat website.py
import sys
import os.path
sys.path.insert(0, os.path.dirname(__file__))
from app import app as application

Files in fido directory.

root@fido:/var/www/fido# tree .
.
├── app.py
├── __init__.py
└── website.wsgi

0 directories, 3 files

Step 5 - Virtual env and dependencies

root@fido:/var/www/fido# virtualenv --no-site-packages env
root@fido:/var/www/fido# . env/bin/activate
(env)root@fido:/var/www/fido# pip install flask sqlalchemy flask-sqlalchemy psycopg2

Step 6 - final setup

Create uwsgi config file

# Add following lines to fido.ini file
root@fido:/etc# cat uwsgi/apps-enabled/fido.ini
[uwsgi]
socket = 127.0.0.1:5000
threads = 2
master = true
uid = fido
gid = fido
chdir = /var/www/fido
home = /var/www/fido/env/
pp = ..
module = website

Check whether uwsgi is booting up properly.

root@fido:/var/www/fido# uwsgi --ini /etc/uwsgi/apps-enabled/fido.ini
...
...
Python version: 2.7.5+ (default, Sep 19 2013, 13:52:09)  [GCC 4.8.1]
Set PythonHome to /var/www/fido/env/
Python main interpreter initialized at 0xb96a70
python threads support enabled
your server socket listen backlog is limited to 100 connections
your mercy for graceful operations on workers is 60 seconds
mapped 165920 bytes (162 KB) for 2 cores
*** Operational MODE: threaded ***
added ../ to pythonpath.
WSGI app 0 (mountpoint='') ready in 1 seconds on interpreter 0xb96a70 pid:  17559 (default app)
*** uWSGI is running in multiple interpreter mode ***
spawned uWSGI master process (pid: 17559)
spawned uWSGI worker 1 (pid: 17562, cores: 2)

uwsgi is able to load the app without any issues. Kill the uwsgi using keyboard interrupt.

Now lets create table.

root@fido:/var/www/fido# . env/bin/activate
(env)root@fido:/var/www/fido# python app.py
* Running on http://0.0.0.0:3333/
* Restarting with reloader

Exit the program, db.create_all() must have created the table. Normally in production environment, it is advised to use python manage.py db create or any similar approach.

Configure nginx

root@fido:/var/www/fido# cat /etc/nginx/sites-enabled/fido.in
upstream flask {
    server 127.0.0.1:5000;
}

# configuration of the server
server {
    # the domain name it will serve for
    listen 127.0.0.1; # This is very important to test the server locally
    server_name fido.in; # substitute your machine's IP address or FQDN
    charset     utf-8;

    location / {
        uwsgi_pass  flask;
        include uwsgi_params;
    }
}

Now nginx and uwsgi will be running in background. Restart them.

root@fido:/var/www/fido# service nginx restart
* Restarting nginx nginx                                                             [ OK ]
root@fido:/var/www/fido# service uwsgi restart
* Restarting app server(s) uwsgi                                                    [ OK ]

Machine name is fido, so lets try curl http://fido

root@fido:/var/www/fido# curl http://fido
Index page. Use /new create a new todo

Create a new task.

root@fido:/var/www/fido#curl --data "name=write blog post about flask deployment"  http://fido/new
Created todo: write blog post about flask deployment

We have successfully deployed flask + uwsgi + nginx.

Since we installed uwsgi from ubuntu repo, it is started as upstart process, that is why we issue commands like service uwsgi restart.

To see all upstart service, try service --status-all.

If you are running multiple web application in a single server, create one user per application.