Ask HN: How does your IT group interact with your developers?

I'm curious to know how developers and IT interact within other companies. I'm a CTO of a company that has 18 developers and 2 IT. One of my IT guys has decided to pursue other interests and he is leaving the company. I always take these opportunities to re-think a little bit how the team is setup and whether we should change our mind on who the right person is to fill in the role that is departing. As such I'm looking for feedback on some questions that many of you may be able to share your wisdom.

For the people that either work in a small/medium company, I'm curious to know what type of IT individuals you have. Are they mainly developers? Are they server administrators? A combination of both?

How does the IT group interact with the developers? Do they both work on the architecture together or are the developers responsible for the architecture and the IT group implements it?

Does the IT group report to the development manager or are fully separated from development?

Any insight is appreciated!