First: get your mind right. Your interviewer is going to try and stump you, just to see how you react. This might not be true for a junior entry position, but you should always expect it. When I interviewed at Dyn, they asked me to white-board a high availability infrastructure that could move around DoS attacks. The point is, they want to see how you do when you don't know all the answers. Designing something like that takes teams of people, so don't bullshit, and don't guess. Solving it with a statement of "I don't know how to set this capability up, but I now it exists and the basic capabilities would help this problem, so I would implement it here" is very acceptable.
Third: Have confidence. You obtain this confidence by defining what you want to become in your career. When asked questions, try to slip in wherever you can that: you know who you are, what you want to be, and how you’re planning on getting there. The weaknesses example above is a perfect intro to explain these goals. For me it sounds something like this:
"My goal is to be an industry respected member of the Devops and open source community by having a significant contribution to a high profile project. I aspire to achieve this by becoming an architect of large scale complex systems and eventually be a guest speaker at technical conferences to inspire and influence other Devops minded engineers"
Fourth: have stumper questions of your own to ask. This is your money maker. Come up with questions for your interviewer that make him think really hard, or intellectually unseat him. Most people try to hire people that are smarter than them. When it is your turn to ask the questions, turn up the heat, and show them how much you prepared, and how intelligent you are. This is also where you find out what type of company you are going to work for. Companies have their own culture, personality, and faults just as much as humans. Treat this like a speed dating round, because you will spend enough time with the company that it is no different than a marriage.
Here are some of my favorite questions:
- Where is an area that you feel needs improvement (technology wise,) that is not getting much traction within the organization.
- What is the single largest technical problem facing your staff, what is currently being done about it, and what types of tasks would I be performing to help you solve this problem?
- Is this a new position? If not, why did the previous owner leave?
- What percentage of job positions are filled from within the company via promotion?
- What are the current quarterly goals of the department I will be working in?
- What are some examples of projects currently being worked on by members of this team?
- What are some examples of things that a current employee is doing that sets them ahead of their peers?