HTTP Persistent Connections

External

• HTTP Keepalive http://web.archive.org/web/20100813132504/http://www.io.com/~maus/HttpKeepAlive.html
• Akamai Support of Persistent Connections https://community.akamai.com/thread/1192

Internal

• Keep-Alive
• HTTP
• httpd Persistent Connection Configuration

Overview

A HTTP persistent connection is a TCP/IP connection between the client and server that allows more that one request per connection.

It is the client that initially requests the connection to be kept alive. In HTTP 1.1, a persistent connection is initiated by specifying a "Keep-Alive" value for the "Connection" request header:

GET ... HTTP/1.1
Host: ...
Connection: Keep-Alive

The server may or may not support persistent connections. If the server does support them, it will confirm that by including with the response a "Connection" response header:

200 OK
Content-Length: ...
Connection: Keep-Alive

Once both the client and the server have agreed on using persistent connections, they will keep the underlying TCP/IP connection open, and subsequent requests from that client will be sent over the persistent connection.

Advantages

• Both the client and the server avoid multiple TCP and SSL handshakes.
• The network throughput is increasing by avoiding TCP slowstart algorithms.

Configuration

For details on how to configure HTTP persistent connections with httpd, see:

httpd Persistent Connection Configuration