Intercepting USR1 in a module

[Maxim Dounin]

Hello!

On Thu, Feb 13, 2014 at 11:15:41AM +1100, Andrew Punch wrote:

> Hi,
> 
> I am maintaining a custom module for nginx. We currently rotate our logs
> and load dynamic data every 5 minutes by using SIGHUP. Unfortunately this
> is also tears down our keepalive connections which harms our performance
> (we are handling about 1500 requests per second per server). We have a
> number of custom log files in addition to the access log and error log
> which also need to be rotated.
> 
> I was hoping that I could use SIGUSR1 to reopen the logs (including the
> module's custom logs) and notify the module that it should reload the
> dynamic data without dropping the keepalive connections.
> 
> I can see that I could use ngx_conf_open_file() to open the module's custom
> log files so that nginx will take care of reopening them. However for
> reloading the dynamic data: I can't see a way to hook the SIGUSR1 in the
> worker process (which shows up as a NGX_CMD_REOPEN in the channel for the
> worker process). However if I added a new hook for NGX_CMD_REOPEN then
> epoll inside the channel handler would probably return EEXIST.
> 
> So what is the best way for a module to hook NGX_CMD_REOPEN? Or is there
> better way of approaching this?

Take a look at ngx_open_file_t's flush() handler.  E.g., it is 
used by ngx_http_log_module to flush buffered/gzipped logs before 
reopen.

-- 
Maxim Dounin
http://nginx.org/