I've setup a cluster of physical servers. Each server runs exactly the same
code. Moreover, each server runs multiple node processes using the build
in cluster functionality.

I use MongoDB (native) to share information between processes and servers.
However, I am having some difficulty with running a special task that needs
to be executed only once during initialization:

Originally I figured that I could read from the MongoDB master server on
each node and check if the admin account already exists. If it does not
then another node has not yet created it, so this node should do so.
However this is problematic because creating an admin password hash is
asynchronous and takes time. Therefore there is a delay between when a node
decides to create the account and when the account is being found by other
nodes when querying the database.

The code snippet that reads from the Mongo master only and creates the
account is available here: https://gist.github.com/3839429

In the future I would also like a special task to be executed every 5
minutes. This task must then only be executed by a running server, and not
by all servers.

In short: when running a cluster of servers, how do you coordinate between
these servers which of them is going to execute a sole task such as the one
described above?

Tom