For dynamic reconfiguration, which is the main file?

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http://wiki.ros.org/dynamic_reconfigu...

In these tutorials, they have shown to create 1) a config file 2) a client file 3) a server file

I want to dynamically reconfigure the HSV values for upper range and lower range of a red color with my code. For that I understand that I need to make a config file first (after creating the package and all those basic stuff..)

But then, other than that, do I need to have these two files -client file and server file other than my main node (that contains the code and where the variables to be configured exist originally)

OR

The main node is basically the client one?

OR

Is it the server one?