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1. ssh into Host $HOST_WITH_ENRICHMENT_TAG as root
2. Create a Squid Grok parser configuration file at /usr/metron/$METRON_RELEASE/config/zookeeper/parsers/squid.json with the following contents: 

   
   {
    "parserClassName": "org.apache.metron.parsers.GrokParser",
    "sensorTopic": "squid",
    "parserConfig": {
    "grokPath": "/apps/metron/patterns/squid",
    "patternLabel": "SQUID_DELIMITED",
    "timestampField": "timestamp"
    },
    "fieldTransformations" : [
      {
        "transformation" : "MTL"
       ,"output" : [ "full_hostname", "domain_without_subdomains" ]
       ,"config" : {
                     "full_hostname" : "URL_TO_HOST(url)"
                    ,"domain_without_subdomains" : "DOMAIN_REMOVE_SUBDOMAINS(full_hostname)"
                   }
       }
     ]

    }

    

3. Notice the use of the fieldTransformations in the parser configuration.  Our Grok Parser is set up to extract the URL, but really we want just the domain or even the domain without subdomains.  To do this, we can use the Metron Transformation Language field transformation.  The Metron Transformation Language is a Domain Specific Language which allows users to define extra transformations to be done on the messages flowing through the topology.  It supports a wide range of common network and string related functions as well as function composition and list operations.  In our case, we extract the hostname from the URL via the URL_TO_HOST function and remove the domain names with DOMAIN_REMOVE_SUBDOMAINS thereby creating two new fields, "full_hostname" and "domain_without_subdomains" to each message. Image Added
4. All parser configurations are stored in Zookeeper. A script is provided to upload configurations to Zookeeper. 
   1. /usr/metron/$METRON_VERSION/bin/zk_load_configs.sh --mode PUSH -i /usr/metron/$METRON_VERSION/config/zookeeper -z $ZOOKEEPER:2181 

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