syslog – UDP local to rsyslog and send remote with TCP and compression

This article is to show how to log Nginx’s access logs locally using UDP to the local rsyslog daemon, which will send the logs to a remote rsyslog server using TCP and compression. In general, logs could generate a lot of traffic and using UDP over distant locations could result in packet loss respectively logs’ lines loss. The idea here is to log messages locally using UDP (non-blocking way) to a local Syslog server, which will send the stream to a remote central Syslog server using TCP connections to be sure no packets are lost. In addition, we are going to enable local caching (if the remote server is temporary unreachable) and compression between the two Syslog servers.
Our goal is to use

  • UDP for our client program (Nginx in the case) for non-blocking log writes.
  • TCP between our local machine and the remote syslog server – to be sure not to lose messages on bad connectivity.
  • local caching for our client machine – not to lose messages if the remote syslog is temporary unreachable.
  • compression between the local machine and the remote syslog server.

The configuration and the commands are tested on CentOS 7, CentOS 8 and Ubuntu 18 LTS. Check out UDP remote logging here – nginx remote logging to UDP rsyslog server (CentOS 7).

STEP 1) Configure client’s local rsyslog to accept UDP log messages only if the messages’ tags are “nginx”

Couple of things should be enabled in the local client-size rsyslog daemon:

  • rsyslog to accept UDP messages. Uncomment or add the following under section “Modules” (probably the first section in the file?) in /etc/rsyslog.conf
    $ModLoad imudp
    $UDPServerRun 514
    

    or

    module(load="imudp")
    input(type="imudp" port="514")
    

    The first is the old syntax, which is still supported and the second is the new syntax. F simplicity, all of the following configuration will be using the new syntax, because the old one is depricated.

  • Add a rule to catch the tag containing “nginx” and execute action to forward the messages to the remote server
    if ($syslogtag == 'nginx:') then {
    action(type="omfwd" target="10.10.10.10" port="10514" protocol="tcp" compression.Mode="single" ZipLevel="9"
    queue.filename="forwarding" queue.spoolDirectory="/var/log" queue.size="1000000" queue.type="LinkedList" queue.maxFileSize="1g" queue.SaveOnShutdown="on"
    action.resumeRetryCount="-1")
    & stop
    }
    
  • The options are almost self-explanatory, the important ones are there is no retry limit count of reconnecting to the server, there is in-disk cache of maximum 1G if the remote server is unavailable and the compression per message is turned on. More on actionshttps://www.rsyslog.com/doc/v8-stable/configuration/actions.html, the forward modulehttps://www.rsyslog.com/doc/v8-stable/configuration/modules/omfwd.html and the queuehttps://www.rsyslog.com/doc/v8-stable/rainerscript/queue_parameters.html

And restart the rsyslog:

systemctl restart rsyslog

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