Meta directories synchronize the identity data from multiple sources via a push or pull protocols, configuration files, etc. They are useful for synchronizing, reconciling, and cleaning data from multiple applications, particularly systems that have their own identity store or do not use a common access mechanism to get their identity data. Many of those applications will not change, so synchronizing with a metadirectory works well.
Virtual directories are useful to pull identity data through the hub from various sources dynamically when an application requests it. This is needed in highly connected environments with dynamic data, and where the application uses a protocol which can be connected to the virtual directory service. I am also well aware that virtual directory fans will want to point out that the authoritative data source is not the service itself, but my point here is that, if the owners shut down the central service, applications can’t access the data. It’s still a political hub.
Personally, I think all this meta and virtual stuff are useful additions to THE key identity hub technology — directory services. When it comes to good old-fashioned, solid scalable, secure directory services, I even have a personal favorite. But I digress.
The key point here as I see it is ‘hub’ vs. ‘bus’ — a central hub service vs. passing identity data between services along the bus.
The meta/virtual/directory administration and configuration is the limiting problem. In directory-speak, the meta/virtual/directory must support the union of all schema of all applications that use it. That means it’s not the mass of data, or speed of synchronization that’s the problem — it’s the political mass of control of the hub that becomes immovable as more and more applications rendezvous on it.
A hub is like the proverbial silo. In the case of meta/virtual/directories the problem goes beyond the inflexibility of large identity silos like Yahoo and Google — those silos support a limited set of very tightly coupled applications. In enterprise deployments, many more applications access the same meta/virtual/directory service. As those applications come and go, new versions are added, some departments are unwilling to move, the central service must support the union of all identity data types needed by all those applications over time. It’s not whether the service can technically achieve this feat, it’s more an issue of whether the application administrators are willing to wait for delays caused by the political bottleneck that the central service inevitably becomes.
Dale makes other related points that are well worth thinking about. But let me zoom in on the relation between metadirectory and the identity bus.
As Dale points out in his piece, I think of the “bus” as being a “backplane” loosely connecting distributed services. The bus exends forever in all directions, since ultimately distributed computing doesn't have a boundary.
In spite of this, the fabric of distributed services isn't an undifferentiated slate. Services and systems are grouped into continents by the people and organizations running and using them. Let's call these “administrative domains”. Such domains may be defined at any scale – and often overlap.
The magic of the backplane or “bus”, as Stuart Kwan called it, is that we can pass identity claims across loosely coupled systems living in multiple discontinuous administrative domains.
But let's be clear. The administrative domains still continue to exist, and we need to manage and rationalize them as much tomorrow as we did yesterday.
I see metadirectories (meaning directories of directories) as the glue for stitching up these administrative continents so digital objects can be managed and co-ordinated within them.
That is the precondition for hoisting the layer of loosely coupled systems that exists above administrative domains. And I don't think it matters one bit whether a given digital object is accessed by a remote protocol, synchronization, or stapling a set of claims to a message – each has its place.
Complex and interesting issues. And my main concern here is not terminology, but making sure the things we have learned about metadirectory (or whatever you want to call it) are properly integrated into the evolving distributed computing architecture. A lot of us are going to be at the European Identity Conference in Munich later this month, so I look forward to the sessions and discussions that will take place there.