Coding interview question for screening DevOps candidates

Many companies practice coding interview in their developer hiring process. The candidate is asked to solve a programming problem in a fixed time-frame to demonstrate their proficiency in the skill the company is looking to hire for. This practice to a certain degree differentiates candidates who can't do real work but somehow got past the first non-technical interview from those who can.

The question in a coding interview is usually a tricky problem involving the use of data structure or algorithm, because that will test the candidate's fundamental understanding of computer science. What if you are hiring a DevOps person? Clearly data structure and algorithm aren't so critical in DevOps tasks. What kind of question is better for testing DevOps candidate? A lot of recruiters have no clue.

This is a question I have used before and had considerable success with:

Automate the process of granting / revoking SSH access to a group of servers instances to a new developer.

This question is so basic that a candidate who fails to do this cannot call himself a DevOps engineer. SSH public key authentication is fundamental in Linux system administration. Automating process is a fundamental responsibility of a DevOps engineer.

The question is asking if we have a new developer joining the team, how do I grant him access to all our servers with one command or at a click of one button. It requires some research and the candidate is expected to spend half-day with you to work out a solution.

If the candidate doesn't understand SSH public key authentication, you can show him the door. If he writes some shell script doing that, it is likely that he comes from a system admin or system engineer background, and isn't too confident doing scripting in a more modern programming language like Python or Ruby.

If he writes a solution in Python, check his code quality. If he writes a solution with a configuration management tool, he is a real DevOps guy. There is more than a way to solve this problem. Anything that shows automation and is good for maintenance is a good solution.

You can check how he plans ahead and how he properly maintains his code by adding extra requirement like how his solution handles revoking access, handles new server instance.

Good Luck.

EDIT: This article was written quite some time ago. Technology moves fast, some of the ideas in this article need to be updated. Here is a more serious discussion on what type of interview questions to ask when hiring a DevOps engineer.