How to find what cause 503 error?

Server NGINX
1

Hi,everyone.

I am using an nginx 0.6.32 and an apache 2.2 server, running a web
forum, using php and mysql.Apache listen in 127.0.0.1:81,processing
php requests.

It works fine for nearly two month. But today I found my server have
503 Service Temporarily Unavailable too often.After refresh my
browser, the web page quickly became normal.

I checked my server(centos 4.4), free disk spaces,cpu load,all of them
is fine.
I also restart my nginx and apache, still doesn’t work.

And I checked my nginx & apache error logs, still nothing valueable.

So, how can I find what cause my server have 503 error? A debug log can
help?

Thank you.

2

Er…I think I found the problem, but still I didn’t know what cause
it, apache, nginx, or my web forum…

The web serevr have an ip of 1.1.1.1, connect to a firewall. And
another address,2.2.2.2 is in the firewall.

In my dns,bind, for internet user, we give them 2.2.2.2, and using nat
in firewall, mapping to 1.1.1.1. for intranet user, we give them
1.1.1.1,direct access it.
This afternoon, I changed the bind setting, so my intranet user visits
my web server using 2.2.2.2.

I changed the bind setting just now, and my web forum work fine now…

It is strange…I think…

Thank you =_=

2008/9/1, baalchina [email protected]: