As I see it, scalability is the capability of a system to handle a growing amount of loading provided with additional resources, while the reliability will assure the system still respond correctly when under heavy load.
Now, adding more servers to your system is something made possible by the scalability attribute of your system but will not increase the attribute. It will just scale the system.
On the other hand, adding more server could indeed help with reliability of your system if not from else at least because it just unload it.
So, the bottom-line: improved scalability is an enabler for adding more servers and reliability is a consequence of it.
Probably, I got it all wrong.
Joined: Apr 12, 2010
since i have added more webservers it should be able to handle more user requests henceforth growing scalability .
Reliability can depend on a lot of factors than just incoming traffic .So the question still stands ground .
However you will be pleased to know that your answer is correct (read it somewhere) but i can't really get the justification.
I think it will increase both, but since here in the question there is no mention of load increase and
"Reliability is the ability to ensure that the product is trustworthy and dependable for all of its transaction. The system load, for example, should not have any effect on the correctness of the system transaction for a system to be reliable."
So if suppose for some reason 1st webserver is down then other will serve the request with the same response hence the system is reliable.
Joined: Apr 12, 2010
Good point ..but question does not mention load balancing algorithm as well..But may be we can safely assume that reliability is of high concern that scalability so Reliability could be the answer.
Joined: Sep 09, 2008
To better grasp my point let me put this question:
What capability will benefit if you choose a 3-tier architecture over a 1-tier?
You see? Adding more servers prove the scalability of your system but can do nothing to improve it. On the other hand decisions like the one in the question can indeed improve the Scalability.