Skip to main content

Python, Flask, Concurrency and Windows

This blog is for those who have written a program in Python and exposed it as API using Flask. You might have written the python algorithm and will be happy to see the output. With small usage and limited users, it still works by making some configuration changes. Problem arises when you host the same API in Production where multiple users are browsing it.

Why it does not work in Production as local environment?
In production, mutiple requests come to server from mutiple locations. If setup is not tuned to cater to concurrent users, either these requests will make the API down or will be throwing exception like 'Internal server error'.

How can we configure the setup to serve concurrent users?
There are few configuration which you have to keep in mind while designing the eco system to accomodate mutiple users.

  1. Make sure Python is installed on server. Download
  2. Download pip from and run command python
  3. Install Flask using pip commands pip install Flask
  4. Open command prompt, run python [filename].py and check your python file is running using Flask.
  5. Install Apache from Apache Lounge and install it as service. Check http://localhost and apache default page should appear. 
    • Open command prompt and goto Apache directory
    • run httpd.exe -k install
    • Open service.msc and look fot Apache service
    • Right click and run it as Automatic
  6. Install mod_wsgi(component for concurrency) using command pip install mod_wsgi
  7. Run command mod_wsgi-express module-config and this will produce output somthing like LoadModule wsgi_module...These are the directives needed to configure Apache to load mod_usgi.
  8. Copy the above output and paste it in [apache home directoty]/conf/httpd.conf at the bottom of the file. 
  9. Modify the Apache confirguration to listen to desired port. Open [apache home directoty]/conf/extra/httpd-vhosts.conf
    • <VirtualHost *:5000>
    •         ServerAdmin admin-name-here
    •         ServerName localhost:5000
    •        WSGIScriptAlias / "C:/Sumit Bajaj/web.wsgi"
    •         DocumentRoot "C:/Sumit Bajaj"
    •         <Directory "C:/Sumit Bajaj">
    •               Require all granted
    •         </Directory>       
    •         ErrorLog "C:/Sumit Bajaj/logs/error.log"
    •         CustomLog "C:/Sumit Bajaj/logs/access.log" common
    • </VirtualHost>
  10. In the above example "C:/Sumit Bajaj" is directory where python file resides. If web.wsgi file does not exists in the folder, create one. 
  11. Copy these lines into web.wsgi file - 
    • import sys
    • sys.path.insert(0, 'C:\Sumit Bajaj')
    • from app import app as application
  12. After all these steps, your file should be running using mod_usgi on Apache.
  13. Even after your setup is not working. See FAQs below.
Python ecoSystem to support concurrency

Frequently Asked Questions(FAQs)

Apache is giving port not found exception 
Open [apache home directoty]/conf/httpd.conf  and search for 'Listen' and make sure your desired port is added to Listen.

Where mod_wsgi directly exists on windows?
It should be in [Python_directory]/lib/. If you are not able to find, search for web.wsgi file and you will get the directory.

Module is not available
While runnig this experiment, if you get execption 'Module is not available', don't get discouraged. Browse the module on internet and install it.

Can we tune flask to run mutiple threads?
Use"", port="5000", threaded=True) rather than default

After using Flask, mod_usgi and Apache, application is not able to feed concurrent requests

  1. Check your hardware
  2. If server has enough resources to server mutiple request. Check your Python code for improvement. In Python there is concept of Global Interpreter Lock(GIL) is a mutex which prevents access to Python objects for multithreaded environment. You may use threading library and lock the object till its work is completed. Read more on Python threading

Should I run Python on Windows or Linux?
Python and dependent libraries are better supported on Linux OS rather than windows, so I will recommended to use Linux. However, if your exisitng ecoSystem does not support it, nothing to worry. This blog is for you.

Please share your queries in comments and I will put my best to answer. 


Popular posts from this blog

Could not load file or assembly 'Microsoft.Web.Infrastructure'

Could not load file or assembly 'Microsoft.Web.Infrastructure, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35' or one of its dependencies. The system cannot find the file specified. What 'Micorosoft.Web.Infrastructure' does? This dll lets HTTP modules register at run time. Solution to above problem: Copy 'Micorosoft.Web.Infrastructure' dll in bin folder of your project and this problem should be resolved. If you have .Net framework installed on machine, this dll should be present on it. You can search for this dll and copy it in your active project folder.   Alternatively,  you can install this dll using nuget package manager PM> Install-Package Microsoft.Web.Infrastructure -Version 1.0.0 Happy coding!!

Create chatbot in 20 minutes using RASA

This blog will help you create a working chatbot with in 20 minutes. For creating chatbot we need following libraries to be installed- >> Python3 >> Pip3 >> Rasa Lets start installing all libraries & dependencies which are need for creating chatbot. Note: I have used MAC, therefore sharing commands related to it. You can install it on Windows, Linux or any other operating system using respective commands. 1. Install Python3 > brew install python3 > python --version #make sure you have python3 installed 2. Install Pip3 > curl -O > sudo python3 If you get issue related to Frameoworks while installing pip, follow below steps -  > cd /usr/local/lib > mkdir Frameworks > sudo chown -R $(whoami) $(brew --prefix)/* Once installed check pip3 version > pip3 --version After python3 and pip3 is succeffully installed, proceed to next steps. 3. Install Rasa > pip

Running dotnet on Linux

Server: Linux, version SUSE 12 To run dotnet code on Linux, the first and foremost task is to "Install Mono package on linux". Note: Mono is an open implementation of Microsoft's .Net framework, including compilers. It uses the same development libraries on Linux which are being used on Windows. Therefore, if you code and compiled some mono code on Linux,  it will work for Windows as well.       zypper is a package installation tool which is used in this scenario. If zypper is not available, check which package manager tool is installed on server. Furthermore, to verify if zypper is installed or not, type zypper on command line which will show all options if zypper is available on server else it will show 'command not found'. zypper ar -r The above command will download from mentioned URL in a new repository. Here 'ar' stands for 'add repo'. After adding it to repos