Could Puppet-reports be removed once these have been processed by Puppet-dashboard or PuppetDB?

Puppet-reports are using a lot of diskspace in:

/var/lib/puppet/reports
/var/lib/mysql

The assumption is that it stores all reports in the MySQL database, because both paths are about the same size. The resource_statuses table consist of rows that each represent a line in a reports file.

• Can one safely remove the reports in /var/lib/puppet/reports after Puppet-dashboard or PuppetDB has processed them?
• What is the best practice for handling reports?
• Is there a way to make Puppet-dashboard automatically delete the yaml report files after processing them?

Yes you can delete them and I recommend it as well. The docs for Puppet dashboard aren't very opinionated on the ongoing maintenance of the dashboard, but it does need maintenance. I recommend a cron that delete reports in the database after a few days, a second one to remove any orphaned records, and a third to delete processed reports. Mine looks like this:

cd /path/to dashboard ; RAILS_ENV=production rake reports:prune upto=3 unit=day
cd /path/to dashboard ; RAILS_ENV=production rake reports:prune:orphaned
find /var/lib/puppet/var/reports/ -mmin +300 -type f -print0 | xargs -0 -r rm > /dev/null 2>&1

You can tweak the times to what works best for your system. I don't believe the delayed_job contains any functionality to delete processed reports, but you might be able to add it to code.