I had an interesting experience today. Without boring you with the details let's just say I'm no richer for the experience save for providing the catalyst for the following instructional tidbit. The catalyst in this case was a question posed to me. I was asked what the difference was between a Role and a Feature when configuring a Windows server.
Now most of you who have any experience at all in Windows Administration may not necessarily be comfortable with the concepts of Server Roles and Features. It's been a slow but steady evolution from an abstract label to a shortcut in Server Manager.
Since Windows 2000's introduction of Active Directory, the concept of a server role took on new meaning. Instead of being limited to just designating a server as a Primary or Backup Domain controller now we had multiple roles that made the old labels moot.
Yeah, I'm talking about the most confusing collection of server "Roles" ever introduced to the Windows Universe, the FSMO or Flexible Single Master Operation. 5 labels that have confused Windows Administrators for a decade.
I mean, the PDC emulator is fairly intuitive, for example. We know what that's for right? Well only partially because that role handles a lot more than just Primary Domain Controller services for Windows NT (non AD) networks. It also provides Time synchronization, Group Policy replication, and account lockout and password change services for an entire windows domain. If the server that holds this role fails you're going to have a very bad day until you move it to another server.
Relative ID master? All that does is keep all the names on your network unique. It's function is to keep combining computer or user object Identifiers (SIDS) with a pool of unique Identifiers managed by this role (RID) Combining the two values ensures that no two objects on an AD network are alike even if everything else about them is the same. The RID master can't allow its pool of RIDS to go empty or it won't have anything to combine with the new SIDS that come from a new user or computer account. Yeah, that's real obvious.
How about the Infrastructure Master? It's a role and its function is... uhh...Oh yeah, it makes sure that if someone from one domain gets rights to something in another domain their specific information is recognized properly. How come such a serious sounding name for such a tiny function that's so rarely used? Whatever..
Those three roles are considered the "Domain" roles in Active Directory networks. That means they only affect the immediate domain they serve. There are two other roles that are considered Forest or Enterprise level roles. That means they live at the top of your AD network above all the domains (assuming there's more than 1) that branch off of the "trunk" of your "forest".
In case all this talk of Directories and Forests is confusing try a different metaphor. Think of AD in the context of a Phone Book instead of a forest. You usually have one Phone book for a town and it contains all the names and numbers of the people with phones. Those names and numbers can be thought of as domains.
Now say your aunt Bessie changes her phone number. The phone book is going to need to be updated to reflect the change or she'll be very lonely because nobody will be able to call her anymore. That would be sad for Aunt Bessie and nobody wants that!
If the phone company decides to change the area code for your town then all the people listed in the phone book have to tell their out of state relatives what the new area code is or they won't be able to call them anymore. Changing the area code, by the way, would be considered an enterprise event to the people listed in the phone book. So would changing the name of the town by the way.
It's the concept of changing names within an organization that leads us to the first of the two "Forest" or "Enterprise" level roles in Active Directory. Coincidentally, it's called the Domain Naming Master and the simplest way to explain its role is to refer back to our theoretical phone book.
Remember when Aunt Bessie changed her number? Well she's a spry old gal and decided to get hitched up to a nice older gent. That meant her last name changed. To make sure everyone can find the happy newlyweds we'll need to get the phone book entry updated. To accomplish that, she had to call the phone company and ask them to change it. The phone company is responsible for changing Bessie's name in the phone book and they are the only ones that could do it. If the phone company is closed nothing changes just as no domain names throughout the enterprise can change if the Domain Naming Master goes offline.
The second and final enterprise FSMO role is easier to understand since its name is a little more descriptive than the others. It's the Schema Master and if you have any experience with databases its function will be instantly recognizable. If you remember that all the information in Active Directory is stored in a database then you know that something has to control the way its organized. That's the function of the Schema Master along with copying (replicating) any changes that occur to the Schema to the rest of the Enterprise.
Going back to the phone book example, the Schema Master would be the guy who decides how the phone book is going to be organized. Will it be sorted by name or phone number? How much information will each listing contain? These questions are all answered by the guy printing the phone book. He is the Schema Master.
Ok maybe not so dramatic but the Schema Master is an important Role. Without it Active Directory couldn't exist.
I've actually went a bit deeper into FSMO roles than I planned but it's important information. It's also important to know how Microsoft tends to overload their terminology.
In the previous discussion I've laid out what Microsoft defines as a "Role" in the context of functions that support Active Directory. There's another definition of a server role, however, that has nothing to do with supporting Windows but rather defines services for users.
You may have noticed that I haven't said much about "Features" to this point. That has everything to do with Microsoft's overloaded terminology again. In the context of an FSMO role a feature is nothing more than a facility for management of a given role.
In the context of a Server Role, however, features become very important. A Server Role in Windows 2000 and later is designated set of services that support user activities. Examples are File and Print services, Application Server and DNS Server roles. Each of these roles is task based defining a set of services to be offered to users by the server.
Server Roles can be viewed more as containers than mechanisms. They are comprised of programs and services tailored to the support of the role. Features are usually the programs and services that provide the functionality of the role. Think of it as the option list on a new car.
A new car has one role, to provide transportation. It's price, however, is dependent on the number of features it has. A base model won't have as many amenities but will still satisfy the core requirement to provide transportation. Many times you can specify additional equipment to tailor its function to better match your needs. This affords additional functionality or "Features" without affecting the core requirement of providing transportation.
It's really that simple. Roles define a task and features support it.
That's about enough, I really don't want to write the word "Role" anymore..