nginx remote logging to UDP rsyslog server (CentOS 7)

This article will present you all the configuration needed to remotely save access logs of an Nginx web server. All the configuration from the client and server sides is included. The client and the server use CentOS 7 Linux distribution and it the configuration could be used under different Linux distribution. Probably only Selinux rules are kind of specific to the CentOS 7 and the firewalld rules are specific for those who use it as a firewall replacing the iptables. Here is the summary of what to expect:

  • Client-side – nginx configuration
  • Server-side – rsyslog configuration to accept UDP connections
  • Server-side – selinux and firewall configuration

STEP 1) Client-side – the Nginx configuration.

Nginx configuration is pretty simple just a single line with the log template and the IP (and port if not default 514) of the rsyslog server. For the record, this is the official documentation https://nginx.org/en/docs/syslog.html. In addition it worth mentioning there could be multiple access_log directives in a single section to log simultaneously on different targets (and the templates may be different or the same). So you can set the access log output of a section locally and remotely.
Nginx configuration (probably /etc/nginx/nginx.conf or whatever is the organization of your Nginx configuration files.)

server {
     .....
     access_log      /var/log/nginx/example.com_access.log main;
     access_log      syslog:server=10.10.10.2:514,facility=local7,tag=nginx,severity=info main3;
     .....
}

The “main” and “main3” are just names of the logging templates defined earlier (you may check rsyslog remote logging – prevent local messages to appear to see an interesting Nginx logging template).
The error log also could be remotely logged:

error_log syslog:server=10.10.10.3 debug;

STEP 2) Server-side – rsyslog configuration to accept UDP connections.

Of course, if you have not installed the rsyslog it’s high time you installed it with (for CentOS 7):

yum install -y rsyslog

To enable rsyslog to listen for UDP connections your rsyslog configuration file (/etc/rsyslog.conf) must include the following:

$ModLoad imudp
$UDPServerRun 514

Most of the Linux distributions have these two lines commented so you just need to uncomment them by removing the “#” from the beginning of the lines. If the lines are missing just add them under section “MODULES” (it should be near the first lines of the rsyslog configuration file).
Change the 514 with the number you like for the UDP listening port.
Write the client’s incoming lines of information to a different location and prevent merging with the local log messages – rsyslog remote logging – prevent local messages to appear. Include as a first rule under the rules’ section starting with “RULES” of the rsyslog configuration file (/etc/rsyslog.conf):

# Remote logging
$template HostIPtemp,"/mnt/logging/%FROMHOST-IP%.log"
if ($fromhost-ip != "127.0.0.1" ) then ?HostIPtemp
& stop

Logs only of remote hosts are going to be saved under /mnt/logging/.log.
Keep on reading!

rsyslog remote logging – prevent local messages to appear

A tip for those who have a remote user server for their log files. When you set up a remote server you probably don’t want local messages to appear in the logging directory (directories) and here is how you can archive it:
Above all the rules in the configuration file “/etc/rsyslog.conf” (or where it is in your system) you include “if” statement for the local server like this:

# Remote logging
$template HostIPtemp,"/mnt/logging/%FROMHOST-IP%.log"
if ($fromhost-ip != "127.0.0.1" ) then ?HostIPtemp
& stop

The name of the template is “HostIPtemp” and the starting part of the path “/mnt/logging/” may be anything you like.
All the remote messages will be redirected to the template and all the rules after won’t be applied to them because we use the “stop instruction”.

That’s why this rule must be above all rules in the whole rule configuration. Above all rules – probably you will find a commented line with “#### RULES ####”

The above configuration will have the following directory structure:

[root@srv ~]# ls -altr /mnt/logging/
total 2792
drwxr-xr-x. 7 root root    4096 12 Sep 10,05 ..
drwxr-xr-x. 2 root root    4096 12 Sep 13,01 .
-rw-------. 1 root root 2844525 12 Sep 13,01 10.10.10.10.log
-rw-------. 1 root root 1245633 12 Sep 13,01 10.10.10.11.log
-rw-------. 1 root root 9722578 12 Sep 13,01 10.10.10.12.log
-rw-------. 1 root root 1127231 12 Sep 13,01 10.10.10.13.log