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:
> if a special `admin` account does not yet exist in the database, it should be created
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.
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