HackerEarth Technology Stack
Originally posted as Quora answer.
This might take a while, so go grab some popcorn. You are going to enjoy this :)
At HackerEarth, we deeply believe in open-source. Why not, our roots are in there. We use open-source software, hack it according to our needs and create something amazing out of that. At the same time, we don't fear writing a seemingly complex project from scratch and turn it into beautiful piece of code. And we have done that so many times in a very short span.
Our application backend is primarily in Python/Django. We modified django-allauth for some of our custom needs. For example, it allows you to login on all sites - HackerEarth, MyCareerStack, and CodeTable with the same login credentials. We modified the django-threadedcomments for spam control (they can really eat you inside!) and enhanced moderator permissions. We wrote our own generic newsfeed system from scratch which can be plugged with any information schema to generate feeds. For example, the feed that you see on MyCareerStack and the recent submissions that you see on HackerEarth, they all come filtered from the same core engine. This feed engine will form one of the core of the upcoming platform and there are some interesting work being done in there - like faster filtering with advanced algorithms, implementation of relevant feed system, and other exciting stuffs. We wrote a notification engine on top of newsfeed system which generates notifications for you. These are part of MyCareerStack for now but as we integrate everything, they will be core of the whole product. We also wrote a generic poll application which tracks all the actions of a user on any item. For example, upvote/downvote on a question, like/dislike on a tutorial, etc. are all powered and regulated by the same application. These user actions can be easily integrated with any object model e.g. programming problem with small snippets of code. As this application develops, we will make it open-source eventually. We did some nice hack with the avatar application to make the image loads faster from Amazon S3. Similarly, we messed around with apache-solr to customize some of the backends involved in searching.
And all this is just a fraction. Currently there are around 60 django applications written in a very generic and modular way which communicate with each other to power everything.
Wait, I haven't told you yet about the amazing stuffs. We wrote the code-checker from scratch, and it's not the usual college project. It is known as CodeFactory Engine internally and forms the core of HackerEarth. The core-engine is written in C and the server is written in C++ using Apache Thrift. It's a very robust client-server architecture with auto-scaling and auto-deployment which gives result of each testcase in real-time. We have built an API around it and we are going to build some amazing things on top of it. Vim plugin to compile/run code using API is just a start. We wrote a realtime server using node.js & nowjs which pushes data to your browser as it gets updated or changed live. The result you get in realtime on submission of program is powered by this server.
In the start of January 2013, we undertook one major task which was not needed very much but we knew it will be essential very soon. We wanted to reduce the page load time using pipelining techniques, similar to BigPipe: Pipelining web pages for high performance. But there wasn't anything out there which we could have been directly integrated. This led to our native implementation of bigpipe, which is still in a very nascent stage. But it brought wonders to the page load time, reducing them by almost half. Another major contribution was of memcached, we integrated it at view level and core level throughout the site. Most of the things are cached, there are systems in place which invalidates and updates them as the data changes. Remember the hit-miss algorithm from Comp. Science 101 ? We did that for webpages!
One weekend in October 2012, we had built the CodeTable to test our CodeFactory server. But then we integrated collaborative coding in it and it went on to become a full-fledged product in itself. It's widely used by someone who wants to hack on some code instantly and share it with others in realtime and doesn't bother about installing compilers/interpreters locally.
All the sites, everything is part of one big project. This keeps us sane and allows us to have greater control. Having said that, as the code base grows over 100,000 lines of code and there are multiple servers running, then there are totally different sets of challenges. There are 5 different servers running right now - apache server, codeFactory server, realtime server, collaboration server, and search server. The apache servers (webserver) and CodeFactory servers are running on few different EC2 instances at any given moment. We wrote custom auto-deployment scripts, builder & developer tools to make the life easy and improve the productivity of our own. We have been using Git from day zero to manage all the source code and have written some nice hooks and wrappers on top of it to abstract a few tasks.
And we have done all this with just two of us working full time since October 2012, and that too with so many things going around with us. I am still a college student! Two others joined to work remotely from January and their contribution has been significant too. And you might acknowledge from all this that we don't fear anything, we deploy fast, we fail fast and are growing aggressively. We still work the way we used to work in college - enjoying life each and every day. We are expanding the team in summer and are going to release tons of cool products that you will love and programmers will love. But most importantly, that will disrupt the way tech recruitment is done in India.
And all this has not been for nothing. Our user base have increased significantly in past few months. Many companies have become our customers. And we are working resolutely towards solving the problem we have to set out to - i.e. to connect smart programmers to awesome product companies coming out of India!
If all this sounds interesting and exciting to you, let's have a chat. Email me at email@example.com, and I will be as enthusiastic to talk to you as you will be! You can also find me @vivekprakash.
Posted by Vivek Prakash, Co-founder - HackerEarth