A grok pattern for Rails 3.2 logs for use with logstash. Assumes that you have a multiline filter to combine Rails logs into one line and only one worker is logging to a file (c.f. https://gist.github.com/mudge/5063930).

logstash.conf

  multiline {
    tags => ["rails"]
    pattern => "^Started"
    negate => true
    what => "previous"
  }

rails

RAILS3 (?m)Started %{WORD:verb} "%{URIPATHPARAM:request}" for %{IPORHOST:clientip} at (?<timestamp>%{YEAR:year}-%{MONTHNUM:month}-%{MONTHDAY:day} %{HOUR:hour}:%{MINUTE:minute}:%{SECOND:second} %{ISO8601_TIMEZONE:timezone})\s*Processing by (?<controller>[^#]+)#(?<action>\w+) as (?<format>\S+)(?:\n  Parameters: %{DATA:params}\n)?%{DATA}Completed %{NUMBER:response}%{DATA} in %{NUMBER:totalms}ms \(Views: %{NUMBER:viewms}ms \| ActiveRecord: %{NUMBER:activerecordms}ms%{GREEDYDATA}

Here's a derivative version that I made, which uses Filebeat to combine multiline messages instead of Logstash (so LS groks the multiline message). Tested with :uuid enabled on Unicorn and Thin, with Rails 3.
https://gist.github.com/excalq/0c5023fce8af90089040daa6404525f2