Using syslog in rails application

Question

I am thinking of using syslog in my rails applications. The process is outlined in this blog post:

1. Add gem 'SyslogLogger' to your Gemfile
2. Add require 'syslog_logger' to the top of config/environments/production.rb
3. Also uncomment the config.logger = line in the same file.

In production box I have 4 rails applications running using passenger. If I switch to use syslogger for all 4 of my applications then I am afraid that the log messages from all 4 applications will go to a single file and the log messages will be interleaving. Of course, I can use splunk but first I wanted to check if it was possible for me to get one log file for each of my rails application. That would be desirable for my situation.

Is that possible?

Answer 1

Yes, by default, almost all Unix syslogds will write messages given in the user or local* facility in the same file. However, every syslogd I know will allow you to specify logfiles on a per-facility basis, so you can have your first application log to local1.*, second one to local2.* and so on.

Furthermore, newer syslog daemons like syslog-ng allow for splitting messages to different files by evaluating the message against a regular expression (write log strings which have railsapp_1 in them to /var/log/railsapp_1.log and so on).

So, configure your syslogd appropriately and you are done (the gory details of changing that configuration should be asked on serverfault.com if your system's man pages don't help you doing it.)

Answer 2

@cite's answer covers one option for distinguishing the apps. However, the syslog message framing actually has 2 fields that make it even easier: hostname and tag (more commonly known and used as program name).

hostname is set by the system syslog daemon before it forwards the message to a centralized server. It will be the same for all apps on the same system but may be handy as you grow past 1 server.

The more interesting one is tag. Your app defines tag when it instantiates SyslogLogger. For example:

SyslogLogger.new('app1')

The logger class will send to the system syslogd as app1, and that appear in both the local log file and any remote syslog destinations (without needing to modify the log message itself). The default is rails. All modern syslog daemons can filter based on tag; see program() for syslog-ng and $programname for rsyslog.

Also, it's worth noting that SyslogLogger is basically wrapping the C openlog() and syslog() functions, so basically all post-log configuration happens on the system daemon. Generally that's desirable, but sometimes you may want your Rails app to log directly to a specific destination (like to simplify automated deployment, change attributes not allowed by syslog(), or run in environments without access to the system daemon).

We ran into a couple of those cases and made a drop-in Logger replacement that generates the UDP packets itself. The remote_syslog_logger gem is on GitHub.