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The Grok processor uses pattern matching to structure and extract important keys from unstructured data.


The following table describes options you can use with the Grok processor to structure your data and make your data easier to query.

Option Required Type Description
break_on_match No Boolean Specifies whether to match all patterns (true) or stop once the first successful match is found (false). Default is true.
grok_when No String Specifies under what condition the grok processor should perform matching. Default is no condition.
keep_empty_captures No Boolean Enables the preservation of null captures from the processed output. Default is false.
keys_to_overwrite No List Specifies which existing keys will be overwritten if there is a capture with the same key value. Default is [].
match No Map Specifies which keys should match specific patterns. Default is an empty response body.
named_captures_only No Boolean Specifies whether to keep only named captures. Default is true.
pattern_definitions No Map Allows for a custom pattern that can be used inline inside the response body. Default is an empty response body.
patterns_directories No List Specifies which directory paths contain the custom pattern files. Default is an empty list.
pattern_files_glob No String Specifies which pattern files to use from the directories specified for pattern_directories. Default is *.
target_key No String Specifies a parent-level key used to store all captures. Default value is null.
timeout_millis No Integer The maximum amount of time during which matching occurs. Setting to 0 prevents any matching from occurring. Default is 30,000.
performance_metadata No Boolean Whether or not to add the performance metadata to events. Default is false. For more information, see Grok performance metadata.

Conditional grok

The grok processor can be configured to run conditionally by using the grok_when option. The following is an example Grok processor configuration that uses grok_when:

  - grok:
      grok_when: '/type == "ipv4"'
          message: ['%{IPV4:clientip} %{WORD:request} %{POSINT:bytes}']
  - grok:
      grok_when: '/type == "ipv6"'
          message: ['%{IPV6:clientip} %{WORD:request} %{POSINT:bytes}']

The grok_when option can take a conditional expression. This expression is detailed in the Expression syntax documentation.

Grok performance metadata

When the performance_metadata option is set to true, the grok processor adds the following metadata keys to each event:

  • _total_grok_processing_time: The total amount of time, in milliseconds, that the grok processor takes to match the event. This is the sum of the processing time based on all of the grok processors that ran on the event and have the performance_metadata option enabled.
  • _total_grok_patterns_attempted: The total number of grok pattern match attempts across all grok processors that ran on the event.

To include Grok performance metadata when the event is sent to the sink inside the pipeline, use the add_entries processor to describe the metadata you want to include, as shown in the following example:

    - grok:
        performance_metadata: true
          log: "%{COMMONAPACHELOG"}
    - add_entries:
          - add_when: 'getMetadata("_total_grok_patterns_attempted") != null'
            key: "grok_patterns_attempted"
            value_expression: 'getMetadata("_total_grok_patterns_attempted")'
          - add_when: 'getMetadata("_total_grok_processing_time") != null'
            key: "grok_time_spent"
            value_expression: 'getMetadata("_total_grok_processing_time")'


The following table describes common Abstract processor metrics.

Metric name Type Description
recordsIn Counter Metric representing the ingress of records to a pipeline component.
recordsOut Counter Metric representing the egress of records from a pipeline component.
timeElapsed Timer Metric representing the time elapsed during execution of a pipeline component.

The Grok processor includes the following custom metrics.


  • grokProcessingMismatch: Records the number of records that did not match any of the patterns specified in the match field.
  • grokProcessingMatch: Records the number of records that matched at least one pattern from the match field.
  • grokProcessingErrors: Records the total number of record processing errors.
  • grokProcessingTimeouts: Records the total number of records that timed out while matching.


  • grokProcessingTime: The time taken by individual records to match against match patterns. The avg metric is the most useful metric for this timer because because it provides the average time taken to match records.
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