DDoS attack case study - Korean election watchdog's site [closed]

Is it possible to break only some of a web site services using DDoS?

For example, disabling only the search feature of a specific website.

I raise this question following a controversy in South Korea, where part of the election watchdog's web site was down during an election. The government claimed it's due to a DDoS attack but many people in Korea do not beleive that story.

Related news: http://thevotingnews.com/international/asia/korea/election-watchdog%E2%80%99s-website-attacked-by-ddos-korea-herald/

When you do a DDoS (or DoS) attack the basic idea is to take down the resource by overloading it with requests. What effect the attack will have depends on the server(s) and the configuration.

In some case you will be able to take down the entire site by attacking the web servers, or some other critical resource (like database server). But some functions may be hosted on a separate server (like a search function), or even hosted by a separate company (like google, facebook, ...). If that external resource is attacked, only that function will be down while the rest of the site works normally.

I would think that if a.exampleserver.com's search utility was sending all queries to a database on b.exampleserver.com, then a successful DDoS attack on b.examplserver.com would allow the website on a.exampleserver.com to continue to run, but with a failed search feature.