Issue: logstash module's `format: json` not work and json pipeline not matched?

[youzipi]

the former question is because my filebeat config not create the json pipeline in es.
I send it by modify the default format.
Now I have new questions ,as described in the issue.
I cannot create the json pipeline by the config shown in document.

Q1:
Can anyone tell me where the default pipeline from
or how can I use custom pipeline for specific module from filebeat side?
Q2:
I cloned the source code, but i donot find how the module config parsed.

Issue: logstash module's `format: json` not make effect and json pipeline not matched

update at
2018-12-06 09:34:09

===================
former question

===================

Hout to config filebeat 6.5.1 logstash modules json decode?

filebeat version: 6.5.1
elk : 6.5.1

I use the logstash modules to tranfer my application's log to ELK.
but it's not parsed in elk.
how can i parse the json in filebeat side?

In Kibana, the message body is not parsed , instead it is treated like a string.

config :

// spring-logback.xml
    <appender name="STASH" class="ch.qos.logback.core.rolling.RollingFileAppender">
        <file>logback/center.log</file>
        <rollingPolicy class="ch.qos.logback.core.rolling.TimeBasedRollingPolicy">
            <fileNamePattern>logback/center.%d{yyyy-MM-dd}.log</fileNamePattern>
            <maxHistory>7</maxHistory>
        </rollingPolicy>
        <encoder class="net.logstash.logback.encoder.LogstashEncoder"/>
    </appender>

// ./modules.d/logstash.yml
- module: logstash
  # logs
  log:
    enabled: true

    # Set custom paths for the log files. If left empty,
    # Filebeat will choose the paths depending on your OS.
    var.paths: ["/Users/youzipi/projects/0/ace-security/logback/*.log"]
    # format: json # i tried this, not worked.

i tried configure json decode

processors:
  - decode_json_fields:
    fields: ["logstash"]
    target: ""
    overwrite_keys: true

but it throw an error : Exiting: error unpacking config data: required 'object', but found 'string' in field 'processors.0.target' (source:'filebeat.yml')

I saw the document example, it's a empty string there.

[steffens (Steffen Siering)]

Which Logstash and Elasticsearch versions are you using?

Have you tried not to set target at all:

processors:
  - decode_json_fields:
    fields: ["logstash"]
    overwrite_keys: true

[youzipi]

I go into the wrong path.
The question is that I cannot create the json pipeline by the config shown in document.
I add more infomation and try steps in issue.