Cause: Fluentd buffers the logs which are not immediately flushed to the storage such as Elaticsearch. The buffers are placed in memory, by default.
Consequence: If there are some issue and the fluentd is forced to quit, the buffered logs would have been lost when the fluentd is restarted.
Fix: Instead of placing the buffers in memory, they are configured on the permanent storage.
Result: Even if the fluentd is accidentally restarted, the buffered logs would not be lost.