如何从Logstash上的JSON日志中提取源主机名

Question

i am collecting logs using OSSEC and forwarding JSON logs to logstash using logstash-forwarder. this is my logstash configuration.

input {   
  lumberjack {
    port => 10516
    type => "lumberjack"
    ssl_certificate => "/etc/pki/tls/certs/logstash-forwarder.crt"
    ssl_key => "/etc/pki/tls/private/logstash-forwarder.key"
    codec => json
    }
}

filter {
  json {
    source => "message"
  }
}
output {
  elasticsearch {
    host => localhost
  }
}

i would like to extract the host indicated on "location" field inside the parenthesis and create a dedicated tag because logstash only sees OSSEC as the source host because it forwards the logs. below is the sample output of logstash.

{
  "_index": "logstash-2015.09.23",
  "_type": "ossec-alerts",
  "_id": "AU_4Q1Hc5OjGfEBnRiWa",
  "_score": null,
  "_source": {
    "rule": {
      "level": 3,
      "comment": "Nginx error message.",
      "sidid": 31301
    },
    "srcip": "192.168.192.10",
    "location": "(logstash) 192.168.212.104->/var/log/nginx/error.log",
    "full_log": "2015/09/23 11:33:24 [error] 1057#0: *562 connect() failed (111: Connection refused) while connecting to upstream, client: 192.168.192.10, server: _, request: \"POST /elasticsearch/.kibana/__kibanaQueryValidator/_validate/query?explain=true&ignore_unavailable=true HTTP/1.1\", upstream: \"http://[::1]:5601/elasticsearch/.kibana/__kibanaQueryValidator/_validate/query?explain=true&ignore_unavailable=true\", host: \"192.168.212.104\", referrer: \"http://192.168.212.104/\"",
    "@version": "1",
    "@timestamp": "2015-09-23T03:33:25.588Z",
    "type": "ossec-alerts",
    "file": "/var/ossec/logs/alerts/alerts.json",
    "host": "ossec",
    "offset": "51048"
  },
  "fields": {
    "@timestamp": [
      1442979205588
    ]
  },
  "sort": [
    1442979205588
  ]
}

Answer 1

Once you apply the json{} filter, you're left with a bunch of fields. You can now apply more filters to those fields, including grok{} for making more fields!

Answer 2

What you need is the grok filter . You can use the grok debugger to find the best patterns for you. The following pattern should work for your location field:

\(%{HOST:host}\) %{IP:srcip}->%{PATH:path}

In logstash filter section :

grok {
    match => { "location" => "\(%{HOST:host}\) %{IP:srcip}->%{PATH:path}" }
    overwrite => [ "host", "srcip" ]
}

overwrite is necessary because you already have fields host and srcip .