OSF DCE Application Development Guide--Core Components

OSF DCE Application Development Guide—Core Components
14.3.3 Strategies for Using Directory Service Entries
When developing an RPC application, decide how an application will use the
namespace and design your application accordingly. The following subsections
discuss issues associated with how servers use different types of directory service
entries.
14.3.3.1 Using Server Entries
An application requires separate server entries for servers on different hosts. For
example, if a server offering the calendar service runs on two hosts, JULES and
VERNE, one server entry is necessary for the server on JULES and another is
necessary for the server on VERNE.
Each server entry requires a unique cell-relative entry name. If a server adheres to a
simple and consistent arrangement of server entries, you may be able to use server
initialization code to automatically generate a name for each server entry, and also to
ensure that the entry exists. However, some servers will need to obtain the entry name
of a server entry from an external source such as a command-line argument or a local
database belonging to the application.
Note: Applications that obtain entry names and UUIDs as command-line
arguments should accept user-defined values that represent them as an
alternative to accepting the actual names.
Some applications, such as a process-control application, require only one server
instance per system. Many applications, however, can accommodate multiple server
instances on a system. When multiple instances of a server run simultaneously on a
single system, all instances on a host can use a single server entry, every instance can
use separate server entries, or the instances can be classified into subsets with a
separate server entry. A client importing from a shared server entry cannot distinguish
among the server instances that export to the entry. Therefore, the recommended
strategy for a server on a given system depends on which server instances are viewed
by clients as interchangeable entities and which are viewed as unique entities, as
follows:
• Interchangeable server instances
When clients consider all the server instances on a host as equivalent alternatives,
all of the instances can (and should) share a server entry. For example, multiple
instances of the calendar service running on host JULES can all export to the
calendar_JULES entry.
• Unique server instances
A unique server instance possesses a significant difference from other instances of
the same host. Unique server instances require separate server entries. Each
server instance must export unique information to its own server entry; this unique
information can be either a server-specific, well-known endpoint or an object
UUID belonging exclusively to the one server instance.
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