On provisioning system I wrote once, I needed to be able to perform multiple tasks in a linear order to complete setting up an account, jobs could be of type: enum { sqlinsert, sqlselect, sqlupdate, shell_exec, …} – each job could also return a list of A/V pairs back to the process flow logic, so that later jobs could get access to that data … Obviously in C/C++ maps and lists are strongly typecast, so it becomes difficult to store different types of object in a single container, unless you start using void* pointers, which isn’t nice.

So, every class implemented a common interface (the list that each job gets added to was typed to that common interface), which allowed me to retrieve the basic formatstring of the command, I could then use an abstract string tokeniser to substitute the real data for the job currently being executed in to it (I never got the point of using regex for this, but would have liked to), and then tell the class to execute the formatted string, without having to worry at that point whether the job was MySQL/Postgres/shell/ldap/whatever, as the run() method you’re calling from the class knows what *it* needs to do internally.

Extremely useful, and was a real time saver for me and kept the code neat, while also allowing me to very easily add new types of datastore in to the provisioning system without having to add huge hunks of extra code.

Why choose BT?

I’m using esxi 3.5 and the reservation for the VIM was set to 512 MB. so i reduced it to 400MB. and it starts my 1 vm now!

i’ll try lowering it more when i need more space for my vms. and post back here so someone else can use it..