Azure – Synchronise Azure Active Directory with OpenLDAP – possible

Stick with the open-source, if I'm reading your question correctly:

• You don't care about Exchange
• You don't have a huge need for minute control of XP settings - I love group policy primarily to save the admin/sales staff from themselves, the developers mostly need me to stay out of their hair
• You're more comfortable with *nix than windows

AD is great at managing windows to a fine degree, but if you don't need that, you're buying yourself a learning curve that won't likely bring a great deal of benefit.

2 caveats

• If you've got the time/interest to push yourself more on the MS side of things, this is a good way to provide that.
• WSUS is a good way to control workstation/server patches. If you can't just flip the "automatic" switch on all machines, this might push the balance over to SBS (if SBS does WSUS?)

Is this possible/feasible?

This is both feasible and common. If you search for something like openldap proxy active directory you'll find a number of useful results.

Is the term "proxy" the good term?

This is absolutely the correct term to use.

Is A Microsoft AD server mandatory or OpenLDAP will do the job fine?

If your clients are only expecting an LDAP server then OpenLDAP will be just fine, particularly if you'll only need read-only access.

I have few knowledge about AD/LDAP, how is the learning curve?

Without knowing your background that's a hard question to answer. I find that LDAP is fundamentally simple, but wrapping your head around access control in OpenLDAP can take a little work.

A few hints where to begin?

If all you need to do is making the AD server available within your local network, then a simple TCP proxy or appropriate iptables rules will be much simpler than a full-blown LDAP proxy. The downside of this is that you would need to perform any access control on the Active Directory side of things.

If you decide to go with OpenLDAP as a proxy:

• Step by Step Installation and Configuration of OpenLDAP as Proxy to Active Directory seems to fit the bill from the title, but it's not very good as a guide.

• The Samba documentation has some notes along these lines.

• This article I wrote a few years ago is more than you want, but does have some configuration examples.