The ignore_older is independent to the new files.
If you have used a wildcard in your path setting filebeat will get the new files without any issue and will stop of watching them after given hours.
So for example imagine that today its 2019.01.01 and you want to ignore the files from 2018 for the logs the name log-.log and are under /var/log/example.
If we want to get newer files automatically what you need its to set the paths parameter as follows:
- type: log
This configuration will take newer files, but we also want to ignore files from 2018 at now are 17:00 so I would set ignore older to 17h as follows:
- type: log
With this configuration our filebeat will send to the previusly configured ouput any file which match the pattern "/var/log/example/log-*.log" but which doesn't have more than 17hours with beeying modified.
If you want can modify it to 24h some days before when there is no chance to get data that you dont want to have.
I would test on test environment even the removal of the parameter to check if after create the sincedb filebeat he would read older files or not.
I hope this clarifies your doubts