Writing syslog messages to MySQL, PostgreSQL or any other supported Database
============================================================================

*Written by* \ `Rainer Gerhards <https://rainer.gerhards.net>`_\ *with
some additions by Marc Schiffbauer (2008-02-28)*

Abstract
--------

***In this paper, I describe how to
write***\ `syslog <http://www.monitorware.com/en/topics/syslog/>`_\ ***messages
to
a***\ `MySQL <http://www.mysql.com/>`_\ ***or***\ `PostgreSQL <http://www.postgresql.org/>`_\ ***database.***\ *Having
syslog messages in a database is often handy, especially when you intend
to set up a front-end for viewing them. This paper describes an approach
with*\ `rsyslogd <http://www.rsyslog.com/>`_\ *, an alternative enhanced
syslog daemon natively supporting MySQL and PostgreSQL. I describe the
components needed to be installed and how to configure them. Please note
that as of this writing, rsyslog supports a variety of databases. While
this guide is still MySQL- and PostgreSQL-focused, you can probably use
it together with other ones too. You just need to modify a few
settings.*

Background
----------

In many cases, syslog data is simply written to text files. This
approach has some advantages, most notably it is very fast and
efficient. However, data stored in text files is not readily accessible
for real-time viewing and analysis. To do that, the messages need to be
in a database. There are various ways to store syslog messages in a
database. For example, some have the syslogd write text files which are
later feed via a separate script into the database. Others have written
scripts taking the data (via a pipe) from a non-database-aware syslogd
and store them as they appear. Some others use database-aware syslogds
and make them write the data directly to the database. In this paper, I
use that "direct write" approach. I think it is superior, because the
syslogd itself knows the status of the database connection and thus can
handle it intelligently (well ... hopefully ;)). I use rsyslogd to
accomplish this, simply because I have initiated the rsyslog project with
database-awareness as one goal.

**One word of caution:** while message storage in the database provides
an excellent foundation for interactive analysis, it comes at a cost.
Database i/o is considerably slower than text file i/o. As such,
directly writing to the database makes sense only if your message volume
is low enough to allow a) the syslogd, b) the network, and c) the
database server to catch up with it. Some time ago, I have written a
paper on `optimizing syslog server
performance <http://www.monitorware.com/Common/en/Articles/performance-optimizing-syslog-server.php>`_.
While this paper talks about Window-based solutions, the ideas in it are
generic enough to apply here, too. So it might be worth reading if you
anticipate medium high to high traffic. If you anticipate really high
traffic (or very large traffic spikes), you should seriously consider
forgetting about direct database writes - in my opinion, such a
situation needs either a very specialized system or a different approach
(the text-file-to-database approach might work better for you in this
case).

Overall System Setup
--------------------

In this paper, I concentrate on the server side. If you are thinking
about interactive syslog message review, you probably want to centralize
syslog. In such a scenario, you have multiple machines (the so-called
clients) send their data to a central machine (called server in this
context). While I expect such a setup to be typical when you are
interested in storing messages in the database, I do not describe how to
set it up. This is beyond the scope of this paper. If you search a
little, you will probably find many good descriptions on how to
centralize syslog. If you do that, it might be a good idea to do it
securely, so you might also be interested in my paper on `ssl-encrypting
syslog message
transfer <http://www.rsyslog.com/doc-rsyslog_stunnel.html>`_.

No matter how the messages arrive at the server, their processing is
always the same. So you can use this paper in combination with any
description for centralized syslog reporting.

As I already said, I use rsyslogd on the server. It has intrinsic
support for talking to the supported databases. For obvious reasons, we
also need an instance of MySQL or PostgreSQL running. To keep us
focused, the setup of the database itself is also beyond the scope of
this paper. I assume that you have successfully installed the database
and also have a front-end at hand to work with it (for example,
`phpMyAdmin <http://www.phpmyadmin.net/>`_ or
`phpPgAdmin <http://phppgadmin.sourceforge.net/>`_. Please make sure
that this is installed, actually working and you have a basic
understanding of how to handle it.

Setting up the system
---------------------

You need to download and install rsyslogd first. Obtain it from the
`rsyslog site <http://www.rsyslog.com/>`_. Make sure that you disable
stock syslogd, otherwise you will experience some difficulties. On some
distributions  (Fedora 8 and above, for example), rsyslog may already by
the default syslogd, in which case you obviously do not need to do
anything specific. For many others, there are prebuild packages
available. If you use either, please make sure that you have the
required database plugins for your database available. It usually is a
separate package and typically **not** installed by default.

It is important to understand how rsyslogd talks to the database. In
rsyslogd, there is the concept of "templates". Basically, a template is
a string that includes some replacement characters, which are called
"properties" in rsyslog. Properties are accessed via the "`Property
Replacer <http://www.rsyslog.com/doc-property_replacer.html>`_\ ".
Simply said, you access properties by including their name between
percent signs inside the template. For example, if the syslog message is
"Test", the template "%msg%" would be expanded to "Test". Rsyslogd
supports sending template text as a SQL statement to the database. As
such, the template must be a valid SQL statement. There is no limit in
what the statement might be, but there are some obvious and not so
obvious choices. For example, a template "drop table xxx" is possible,
but does not make an awful lot of sense. In practice, you will always
use an "insert" statement inside the template.

An example: if you would just like to store the msg part of the full
syslog message, you have probably created a table "syslog" with a single
column "message". In such a case, a good template would be "insert into
syslog(message) values ('%msg%')". With the example above, that would be
expanded to "insert into syslog(message) values('Test')". This expanded
string is then sent to the database. It's that easy, no special magic.
The only thing you must ensure is that your template expands to a proper
SQL statement and that this statement matches your database design.

Does that mean you need to create database schema yourself and also must
fully understand rsyslogd's properties? No, that's not needed. Because
we anticipated that folks are probably more interested in getting things
going instead of designing them from scratch. So we have provided a
default schema as well as build-in support for it. This schema also
offers an additional benefit: rsyslog is part of
`Adiscon <http://www.adiscon.com/en/>`_'s `MonitorWare product
line <http://www.monitorware.com/en/>`_ (which includes open source and
closed source members). All of these tools share the same default schema
and know how to operate on it. For this reason, the default schema is
also called the "MonitorWare Schema". If you use it, you can simply add
`phpLogCon, a GPLed syslog web interface <http://www.phplogcon.org/>`_,
to your system and have instant interactive access to your database. So
there are some benefits in using the provided schema.

The schema definition is contained in the file "createDB.sql". It comes
with the rsyslog package and one can be found for each supported
database type (in the plugins directory). Review it to check that the
database name is acceptable for you. Be sure to leave the table and
field names unmodified, because otherwise you need to customize
rsyslogd's default sql template, which we do not do in this paper. Then,
run the script with your favorite SQL client. Double-check that the
table was successfully created.

It is important to note that the correct database encoding must be used
so that the database will accept strings independent of the string
encoding. This is an important part because it can not be guarantied
that all syslog messages will have a defined character encoding. This is
especially true if the rsyslog-Server will collect messages from
different clients and different products.

For example PostgreSQL may refuse to accept messages if you would set
the database encoding to “UTF8” while a client is sending invalid byte
sequences for that encoding.

Database support in rsyslog is integrated via loadable plugin modules.
To use the database functionality, the database plugin must be enabled
in the config file BEFORE the first database table action is used. This
is done by placing the

    ``$ModLoad ommysql``

directive at the beginning of /etc/rsyslog.conf for MySQL and

    ``$ModLoad ompgsql``

for PostgreSQL.

For other databases, use their plugin name (e.g. omoracle).

Next, we need to tell rsyslogd to write data to the database. As we use
the default schema, we do NOT need to define a template for this. We can
use the hardcoded one (rsyslogd handles the proper template linking). So
all we need to do e.g. for MySQL is add a simple selector line to
/etc/rsyslog.conf:

    ``*.*       :ommysql:database-server,database-name,database-userid,database-password``

Again, other databases have other selector names, e.g. ":ompgsql:"
instead of ":ommysql:". See the output plugin's documentation for
details.

In many cases, the database will run on the local machine. In this case,
you can simply use "127.0.0.1" for *database-server*. This can be
especially advisable, if you do not need to expose the database to any
process outside of the local machine. In this case, you can simply bind
it to 127.0.0.1, which provides a quite secure setup. Of course, rsyslog
also supports remote database instances. In that case, use the remote
server name (e.g. mydb.example.com) or IP-address. The *database-name*
by default is "Syslog". If you have modified the default, use your name
here. *Database-userid* and *-password* are the credentials used to
connect to the database. As they are stored in clear text in
rsyslog.conf, that user should have only the least possible privileges.
It is sufficient to grant it INSERT privileges to the systemevents
table, only. As a side note, it is strongly advisable to make the
rsyslog.conf file readable by root only - if you make it world-readable,
everybody could obtain the password (and eventually other vital
information from it). In our example, let's assume you have created a
database user named "syslogwriter" with a password of "topsecret" (just
to say it bluntly: such a password is NOT a good idea...). If your
database is on the local machine, your rsyslog.conf line might look like
in this sample:

    ``*.*       :ommysql:127.0.0.1,Syslog,syslogwriter,topsecret``

Save rsyslog.conf, restart rsyslogd - and you should see syslog messages
being stored in the "systemevents" table!

The example line stores every message to the database. Especially if you
have a high traffic volume, you will probably limit the amount of
messages being logged. This is easy to accomplish: the "write database"
action is just a regular selector line. As such, you can apply normal
selector-line filtering. If, for example, you are only interested in
messages from the mail subsystem, you can use the following selector
line:

    ``mail.*       :ommysql:127.0.0.1,syslog,syslogwriter,topsecret``

Review the
`rsyslog.conf <http://www.rsyslog.com/doc-rsyslog_conf.html>`_
documentation for details on selector lines and their filtering.

**You have now completed everything necessary to store syslog messages
to the a database.** If you would like to try out a front-end, you might
want to look at `phpLogCon <http://www.phplogcon.org/>`_, which displays
syslog data in a browser. As of this writing, phpLogCon is not yet a
powerful tool, but it's open source, so it might be a starting point for
your own solution.

On Reliability...
-----------------

Rsyslogd writes syslog messages directly to the database. This implies
that the database must be available at the time of message arrival. If
the database is offline, no space is left or something else goes wrong -
rsyslogd can not write the database record. If rsyslogd is unable to
store a message, it performs one retry. This is helpful if the database
server was restarted. In this case, the previous connection was broken
but a reconnect immediately succeeds. However, if the database is down
for an extended period of time, an immediate retry does not help.

Message loss in this scenario can easily be prevented with rsyslog. All
you need to do is run the database writer in queued mode. This is now
described in a generic way and I do not intend to duplicate it here. So
please be sure to read "`Handling a massive syslog database insert rate
with
Rsyslog <http://www.rsyslog.com/doc-rsyslog_high_database_rate.html>`_\ ",
which describes the scenario and also includes configuration examples.

Conclusion
----------

With minimal effort, you can use rsyslogd to write syslog messages to a
database. You can even make it absolutely fail-safe and protect it
against database server downtime. Once the messages are arrived there,
you can interactively review and analyze them. In practice, the messages
are also stored in text files for longer-term archival and the databases
are cleared out after some time (to avoid becoming too slow). If you
expect an extremely high syslog message volume, storing it in real-time
to the database may outperform your database server. In such cases,
either filter out some messages or used queued mode (which in general is
recommended with databases).

The method outlined in this paper provides an easy to setup and maintain
solution for most use cases.

References and Additional Material
----------------------------------

-  `www.rsyslog.com <http://www.rsyslog.com/>`_ - the rsyslog site

-  `Paper on Syslog Server
   Optimization <http://www.monitorware.com/Common/en/Articles/performance-optimizing-syslog-server.php>`_
