When flushing to S3 failed more than Retry_Limit, the failed data remains in store_dir. Can I manually flush those data to S3 in Fluentbit?
You can easily force flushing the logs to AWS S3 by sending a SIGUSR1 to td-agent:
sudo kill -USR1 `cat /var/run/td-agent/td-agent.pid`
you should see a message like this in
/var/log/td-agent/td-agent.conf
2019-08-11 14:43:18 +0000 [info]: #0 force flushing buffered events
2019-08-11 14:43:18 +0000 [info]: #0 flushing all buffer forcedly