libbeat: can't override logging.files.name by command line option if filebeat.full.yml is loaded

[cyrilleverrier]

This bug is reproducible with any beats (filebeats, metrics beat, custom beat, etc.)

• Version: libbeat v5.0.0
• Operating System: Linux Ubuntu
• Steps to Reproduce:

1. cd <...>/github.com/elastic/beats/filebeat
2. make
3. ./filebeat -c filebeat.yml -E logging.files.name=override1_filename.log
4. ./filebeat -c filebeat.full.yml -E logging.files.name=override2_filename.log
5. ls logs

Expected result:
In both cases, the log filename is overridden

$ls logs
 override1_filename.log override2_filename.log

Actual result:
The log filename is not overridden if the filebeat.full.yml is loaded

$ls logs
filebeat  override1_filename.log

There is a problem when merging the configuration from file and from command line.

filebeat.full.yml contains the section logging.files but is empty
filebeat.yml does not contain the section logging.files, and get default values

[ruflin]

@urso I think this is related to ucfg. Can you have a look?
@cyrilleverrier Thanks for reporting.

[cyrilleverrier]

note: @urso this bug is still present with ucfg v0.4.4

[urso]

Testing with console output only yet, using -E works for me.

I started PR #3304 adding debug output of config file loaded. This will help debugging the issue.

Will have a look at the described issue tomorrow.

[urso]

fix in progress: elastic/go-ucfg#85