The parser filter plugin "parses" string field in event records and mutates its event record with the parsed result.

It is included in the Fluentd's core.

Example Configurations

<filter foo.bar>
  @type parser
  key_name log
  <parse>
    @type regexp
    expression /^(?<host>[^ ]*) [^ ]* (?<user>[^ ]*) \[(?<time>[^\]]*)\] "(?<method>\S+)(?: +(?<path>[^ ]*) +\S*)?" (?<code>[^ ]*) (?<size>[^ ]*)$/
    time_format %d/%b/%Y:%H:%M:%S %z
  </parse>
</filter>

filter_parser uses built-in parser plugins and your own customized parser plugin, so you can reuse the predefined formats like apache2, json, etc. See Parser Plugin Overview for more details

With this example, if you receive this event:

time:
injected time (depends on your input)
record:
{"log":"192.168.0.1 - - [05/Feb/2018:12:00:00 +0900] \"GET / HTTP/1.1\" 200 777"}

The parsed result will be:

time
05/Feb/2018:12:00:00 +0900
record:
{"host":"192.168.0.1","user":"-","method":"GET","path":"/","code":"200","size":"777"}

Plugin Helpers

• ​parser​

• ​record_accessor​

• ​compat_parameters​

Parameters

See Common Parameters.

<parse> Section

This is a required subsection. Specifies the parser type and related parameter.

For more details, see Parse Section Configurations.

key_name

Specifies the field name in the record to parse.

This parameter supports nested field access via record_accessor syntax.

reserve_time

Keeps the original event time in the parsed result.

<filter foo.bar>
  @type parser
  key_name log
  reserve_time true
  <parse>
    @type json
  </parse>
</filter>

With above configuration, here is the result:

# input data:  {"key":"value","log":"{\"time\":1622473200,\"user\":1}"}

Above incoming event is parsed as:

time:
2021-06-01 00:00:00.000000000 +0900
​
record:
{
  "user": 1
}

The value of time field (1622473200) is reserved as event time (2021-06-01 00:00:00.000000000 +0900).

Without reserve_time, the result is:

# input data:  {"key":"value","log":"{\"time\":1622473200,\"user\":1}"}

Above incoming event is parsed as:

time:
2021-06-24 14:33:35.475115751 +0900 (It vary on parsed timestamp)
​
record:
{
  "user": 1
}

The value of parsed timestamp is set as event time. The value of time field is discarded.

reserve_data

Keeps the original key-value pair in the parsed result.

<filter foo.bar>
  @type parser
  key_name log
  reserve_data true
  <parse>
    @type json
  </parse>
</filter>

With above configuration, here is the result:

# input data:  {"key":"value","log":"{\"user\":1,\"num\":2}"}
# output data: {"key":"value","log":"{\"user\":1,\"num\":2}","user":1,"num":2}

Without reserve_data, the result is:

# input data:  {"key":"value","log":"{\"user\":1,\"num\":2}"}
# output data: {"user":1,"num":2}

remove_key_name_field

Removes key_name field when parsing is succeeded.

<filter foo.bar>
  @type parser
  key_name log
  reserve_data true
  remove_key_name_field true
  <parse>
    @type json
  </parse>
</filter>

With above configuration, here is the result:

# input data:  {"key":"value","log":"{\"user\":1,\"num\":2}"}
# output data: {"key":"value","user":1,"num":2}

replace_invalid_sequence

If true, invalid string is replaced with safe characters and re-parse it.

inject_key_prefix

Stores the parsed values with the specified key name prefix.

<filter foo.bar>
  @type parser
  key_name log
  reserve_data true
  inject_key_prefix data.
  <parse>
    @type json
  </parse>
</filter>

With above configuration, here is the result:

# input data:  {"log": "{\"user\":1,\"num\":2}"}
# output data: {"log":"{\"user\":1,\"num\":2}","data.user":1, "data.num":2}

hash_value_field

Stores the parsed values as a hash value in a field.

<filter foo.bar>
  @type parser
  key_name log
  hash_value_field parsed
  <parse>
    @type json
  </parse>
</filter>

With above configuration, result is below:

# input data:  {"log": "{\"user\":1,\"num\":2}"}
# output data: {"parsed":{"user":1,"num":2}}

emit_invalid_record_to_error

Emits invalid record to @ERROR label. Invalid cases are:

• key does not exist

• the format is not matched

• an unexpected error

You can rescue unexpected format logs in the @ERROR label.

If you want to ignore these errors, set false.

FAQ

suppress_parse_error_log is missing. What are the alternatives?

Since v1, parser filter does not support suppress_parse_error_log parameter because parser filter uses the @ERROR feature instead of internal logging to rescue invalid records. If you want to simply ignore invalid records, set emit_invalid_record_to_error false.

See also emit_invalid_record_to_error parameter.

Learn More

• ​Filter Plugin Overview​

If this article is incorrect or outdated, or omits critical information, please let us know. Fluentd is an open-source project under Cloud Native Computing Foundation (CNCF). All components are available under the Apache 2 License.