Broken Grok filter since V7.10.0

Elastic Stack Logstash
1

Hi ,
I've recently upgraded logstash from V7.6.0 to V7.16.3. and have seen some odd behaviors of Grok filter since then.

filter {
        grok {
                patterns_dir => "C:\software\ELK\config\patterns"

                        match=> { "message" => "%{CFLOG}" }
                        add_tag => "has_traceback"
                        tag_on_failure=>[]
                        break_on_match=>false
                        match=> { "uri_stem" =>"%{REQUESTURL}"}
                        match=> {"uri_stem" =>"%{DATATYPE}"}
                        match=> {"atime" => "%{STIME}"}

CFLOG ^%{CFDATE:adate}\s+%{TIME:atime}\s+%{NOTSPACE:x_edge_location}\s+%{NUMBER:bytes}\s+%{IP:clientip}\s+%{WORD:verb}\s+%{NOTSPACE}\s+%{NOTSPACE:uri_stem}\s+%{NUMBER:response}\s+%{NOTSPACE:referer}\s+%{NOTSPACE:agent}\s+%{NOTSPACE:uri_query}\s+%{NOTSPACE:cookies}\s+%{NOTSPACE:x_edge_result_type}\s+%{NOTSPACE}\s+%{NOTSPACE}\s+%{NOTSPACE:cs_protocol}\s+%{NUMBER:cs_bytes}\s+%{NOTSPACE:time_taken}\s+%{NOTSPACE:x_forwarded_for}\s+%{NOTSPACE:ssl_protocol}\s+%{NOTSPACE:ssl_cipher}\s+%{WORD:x_edge_response_result_type}\s+%{NOTSPACE:cs_protocol_version}

REQUESTURL /(%{URLFRAGMENT:lang}/)?%{LEGTYPE:legtype}/%{LEGYEAR:legyear}/%{URLFRAGMENT:legnum}?%{GREEDYDATA:legrest}

it appears that above rules worked for all versions prior to V.7.10.0. However, the rule match=> { "uri_stem" =>"%{REQUESTURL}"} failed to match and returned empty matches in any version between V7.10.0 and V7.16.3.
I am wondering if there was any breaking changes of Grok syntax at V7.10.0?
I also tried grok rules in Kibana's grok debugger (V7.16.3), all works fine.

Regards,
Landong

2

You are making an assumption about the order in which multiple occurrences of the match option are combined. logstash does not guarantee the order and l know it changed a while back. From first-to-last to last-to-first (I think), so grok is trying to match [uri_stem] before it has been created by matching [message]

As far as I know, order is preserved within a single hash (i.e. a single occurrence of the match option) but the order in which multiple hashes are merged is not defined.

So, do not use multiple occurrences. I would suggest trying

    add_tag => "has_traceback"
    tag_on_failure=>[]
    break_on_match=>false
    match=> { 
        "message" => "%{CFLOG}"
        "uri_stem" =>"%{REQUESTURL}"
        "uri_stem" =>"%{DATATYPE}"
        "atime" => "%{STIME}"
    }

If that does not work then split it into two groks - one for [message] and another for the rest.

3

Thanks Badger,
I did split it into two groks, which produced the expected outcome.

Regards,

Landong

4

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