Can somebody help me to grok this log?

Question

127.0.0.1 - - [21/May/2016:13:43:37 +0200] "GET /images/example.png HTTP/1.1" 304 0 "-" "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:46.0) Gecko/20100101 Firefox/46.0" "-"

Answer 1

It's an Apache log and grok has a pattern dedicated to that which is called COMBINEDAPACHELOG. So your grok can be defined like this:

grok {
   match => {"message" => "%{COMBINEDAPACHELOG}"}
}

You'll get an event like this:

{
        "message" => "127.0.0.1 - - [21/May/2016:13:43:37 +0200] \"GET /images/example.png HTTP/1.1\" 304 0 \"-\" \"Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:46.0) Gecko/20100101 Firefox/46.0\" \"-\"",
       "@version" => "1",
     "@timestamp" => "2016-05-23T07:43:53.439Z",
           "host" => "iMac.local",
       "clientip" => "127.0.0.1",
          "ident" => "-",
           "auth" => "-",
      "timestamp" => "21/May/2016:13:43:37 +0200",
           "verb" => "GET",
        "request" => "/images/example.png",
    "httpversion" => "1.1",
       "response" => "304",
          "bytes" => "0",
       "referrer" => "\"-\"",
          "agent" => "\"Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:46.0) Gecko/20100101 Firefox/46.0\""
}