Sunday, February 1, 2015

Deploy a MongoDB powered Flask app in 5 minutes

This is a quick tutorial to deploy a web service (a social network) by the LNMP (Linux, Nginx, MongoDB, Python) infrastructure on any IaaS cloud. The repo at Github is at


The stack is built on the tools in the ecosystem of Python below. 

Tool Name Advantage
Cloud DigitalOcean Cheap but fast
Server distro Ubuntu 14.10 x64 Everything is latest
WSGI proxy Gunicorn Manage workers automatically
Web proxy Nginx Fast and easy to configure
Framework Flask Single file approach for MVC
Data store MongoDB No scheme needed and scalable
DevOps Fabric Agentless and Pythonic
In addition, a Supervisor running on the server provides a daemon to protect the Gunicorn-Flask process.

The MiniTwit app

The MiniTwit application is an example provided by Flask, which is a prototype of Twitter like multiple-user social network. The original application depends on SQLite. However, the data store could be modified to fit the category of NoSQL such as Google Data Store or MongoDB. A live MintiTwit demo is hosted at


1. Install Fabric and clone the Github repo
The DevOps tool is fabric that is simply based on SSH. The and the staging flask files are stored on Github. We should install fabric and download the on the local machine before the deployment.
sudo pip install fabric 
fab -l
2. Enter IP from the virtual machine
A new VM from ausually emails IP address and the root password. Then we could modify the head part of the accordingly. There are quite a less expensive cloud providers for prototyping other than the costly Amazon EC2. For example, a minimal instance from DigitalOcean only costs five dollars a month. If SSH key has been uploaded, the password could be ignored.
env.hosts = ['YOUR IP ADDRESS'] #  Enter IP
env.user = 'root'
env.password = 'YOUR PASSWORD'  #  Enter password
3. Fire up Fabric
Now it is time to formally deploy the application. With the command below, the fabric will first install pip, git, nginx, gunicorn, supervisor and the latest MongodB, and configure them sequentially. In less than 5 minutes, a Flask and MongoDB application will be ready for use. Since DigitalOcean has its own software repository for Ubuntu, and its VMs are on SSD, the deployment is even faster, which is usually finished in one minute.
fab deploy_minitwit

Good math, bad engineering

As a formal statistician and a current engineer, I feel that a successful engineering project may require both the mathematician’s abilit...