When using Nginx as a reverse proxy where the connections stay open (for example, to implement a server push), a problem arise when the client times out: nginx doesn't detect it because it doesn't use the TCP keepalive mechanism. The fact that nginx doesn't detect connection timeouts implies that the backend server (used for comet, server push, etc..) will see the client as connected forever which is bad for two reasons: 1) the client presence can matter in your application, and 2) resources will never get freed up.

Note: this has nothing to do with HTTP keepalive.

This module allows you to set the TCP keepalive values on http connections, namely TCP_KEEPCNT, TCP_KEEPIDLE, TCP_KEEPINTVL.

Configure the Nginx sources with:

./configure --add-module=path/to/nginx_tcp_keepalive

And then compile/install with make/make install.

• syntax: tcp_keepalive on|off
• default: off
• context: http, server, location

Enables the TCP keepalive mechanism.

• syntax: tcp_keepcnt num
• default: 2
• context: http, server, location

The maximum number of keepalive probes TCP should send before dropping the connection.

• syntax: tcp_keepidle time
• default: 1m
• context: http, server, location

The time the connection needs to remain idle before TCP starts sending keepalive probes.

• syntax: tcp_keepintvl time
• default: 1m
• context: http, server, location

The time between individual keepalive probes.

nginx_tcp_keepalive is distributed under the MIT license.