Pros and Cons of Keep-Alive from Web Server Side

httpkeep-aliveperformancewebserver

Keep-Alive connection feature in HTTP protocol is meant to reduce TCP connection hits to web server. It should be able to improve web server performance. However, I found that some web servers deliberately disable KeepAlive feature from server side.

In my understanding, some reverse proxy, i.e. HAProxy, disables HTTP keep-alive in order to reduce memory usage which is more critical than CPU usage in some situation.

Is there any other reason why Web server disables Keep-Alive?

Best Answer

Actually, Keep-Alive is meant to improve HTTP performance, not server performance (though for SSL connections it does reduce the cost on the server of re-negotiating the encryption). The big win is in the number of round trips the browser has to make to get the content. With Keep-Alive the browser gets to eliminate a full round trip for every request after the first, usually cutting full page load times in half.

Keep-Alive increase server load which is why some shared hosting providers disable it. Each open connection consumes memory as well as a file descriptor (linux) and in extreme cases (some Apache configs) it may have a 1:1 mapping from connections to processes.

Related Solutions

The difference between application server and web server

Most of the times these terms Web Server and Application server are used interchangeably.

Following are some of the key differences in features of Web Server and Application Server:

Web Server is designed to serve HTTP Content. App Server can also serve HTTP Content but is not limited to just HTTP. It can be provided other protocol support such as RMI/RPC
Web Server is mostly designed to serve static content, though most Web Servers have plugins to support scripting languages like Perl, PHP, ASP, JSP etc. through which these servers can generate dynamic HTTP content.
Most of the application servers have Web Server as integral part of them, that means App Server can do whatever Web Server is capable of. Additionally App Server have components and features to support Application level services such as Connection Pooling, Object Pooling, Transaction Support, Messaging services etc.
As web servers are well suited for static content and app servers for dynamic content, most of the production environments have web server acting as reverse proxy to app server. That means while servicing a page request, static contents (such as images/Static HTML) are served by web server that interprets the request. Using some kind of filtering technique (mostly extension of requested resource) web server identifies dynamic content request and transparently forwards to app server

Example of such configuration is Apache Tomcat HTTP Server and Oracle (formerly BEA) WebLogic Server. Apache Tomcat HTTP Server is Web Server and Oracle WebLogic is Application Server.

In some cases the servers are tightly integrated such as IIS and .NET Runtime. IIS is web server. When equipped with .NET runtime environment, IIS is capable of providing application services.

C# – How to disable keep-alive on ASP.NET Web Service client requests

Isn't overriding the GetWebRequest method working:

protected override WebRequest GetWebRequest(Uri uri)
{
    var webRequest = (HttpWebRequest)base.GetWebRequest(uri);
    webRequest.KeepAlive = false;
    return webRequest;
}

Best Answer

Related Solutions

The difference between application server and web server

C# – How to disable keep-alive on ASP.NET Web Service client requests

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