I want to know how to get internship at Codechef.
AFAIK you can’t intern at Codechef. Codechef is a non-profit holding for Directi. Directi is a holding company for Media.net, Ringo, Zeta etc and the Codechef platform.
The Codechef platform doesn’t generate any revenue for them. I had four friends intern with Directi this summer. They all worked on Media.net (Their advertising engine). And Codechef consumes very less resources anyway, since they already use SPOJ as a judge, they probably have a very small team working on Codechef. They would want interns and employees to work on products which generate actual revenue for them (Codechef doesn’t).
In short, apply on the Careers website for Directi and if all goes well they might contact you.
One way to get an internship is by finding a good bug.
Other is by doing someone great thing like getting a medal at IOI.