Architecture is one of those things that isn’t simply a trivia question (e.g., design pattern uses) and is a lot more subjective than other interview topics. There often isn’t a single correct architecture so that makes it trickier to evaluate someone. The most you can get is an idea of how the interviewee thinks.
I would suggest that you describe to the interviewee a complex product or part of a product that you (the interviewer) are most intimately familiar with. Then ask him to think of how he would architect it and explain his reasoning, and then focus on specific decisions and ask questions.
Of course, only do this if:
- You are open to hearing other designs that are not your own.
- You are able to take potential
criticisms and acknowledge that your
own design might be imperfect
An added bonus is that you would see how you might handle disagreements if he is hired.
An alternative approach if your product has ever been rearchitected is to describe the architecture of the old version and ask the interviewee how he would rearchitect it. If the result is close to the current architecture, it is likelier that the candidate would be a good fit with the style and mindset of your group.