I think this is fantastic. I can see your investment pitch being "the HackerRank/LeetCode of devops". I've only tried one scenario (DNS) so far but it seems well done, not too long, not too easy, not too hard. I am excited to try it out further.

First I'll address your questions and then add some comments of my own.

1. I do a lot of technical interviewing. Many people can _sound_ like they know what they're talking about, but it can be a struggle to get to the nitty gritty to really test their understanding. This product seems to have an angle of "take-home tests as a service", which is cool. Over time I can see how you could come to have a large library of scenarios and use of them would be very helpful in filtering candidates for real, demonstrable competence.

2. I like it. I once tried a DIY approach involving having candidates talk to a Kafka server I provided, with client certificates. It was cumbersome. There was a 100% overlap of candidates who succeeded and candidates who could be bothered to take the test at all. From this I gathered that the mere existence of the test was a strong filter, but it's also fair to say that judging test difficulty level well is extremely hard. (In other words: "oh no, he wants me to actually understand how to use client certs? Bye.")

3. Pre-interview. Async hiring process with just-in-time candidate attention means the team does not lose too much productivity (as much as hiring is a valuable use of time, developer time in a small company is at a premium).

Some quick-fire minor comments: consider making it easier to share the test link (I generated it on my phone, wanted to run on my desktop); the password field is before the username; it wasn't super obvious that different VMs were in play between the warmup and real scenario, nor that a scenario could involve multiple VMs itself. Also, you've no doubt thought of this, but have good defences against abuse of your VMs. By the way, have you considered this approach [1] to VMs? More controllable, but less realistic.

Some questions/suggestions:

1. As the test admin I'd love to to provide "verify.sh" to grade the test using logic I specify. My script would test, for example, "Can this VM now reach host X?" "Is command Y in the bash history?" and dump out a report somewhere. -- What ideas do you have for auto-marking?

2. What revenue model do you have in mind?

3. How ready is this for real-life use in a hiring pipeline?

4. Do you think there is future scope for a customer to specify their own scenarios, or is the idea more that you build up a library of them?

5. Have an advanced mode where the candidate must supply a public key to you for SSH access, rather than password. Boom, you've filtered for a basic understanding of public key cryptography.

6. I am not sure the user flow currently has a clear distinction between "recruiter view" and "candidate view" but no doubt that is on the roadmap.

7. Scenario idea: certificate expiry blocking secure comms between hosts. This happens in K8S clusters often enough. Could be replicated here.

8. Just from curiosity, any details you can share about how the stack works? What am I talking to, a docker-compose script of Centos containers? You've done a nice job with the SSH user routing; am I being tunnelled through your jumpbox to the target machine/container?

That's a lot, sorry! I think this is an exciting idea and that you guys are on to something.

[1] https://blog.benjojo.co.uk/post/qemu-monitor-socket-rce-vnc