During source-only mode, the ingested events are stored in a temporary file buffer. After SIGWINCH is sent to the supervisor and this mode is canceled, this buffer begins to load.
By default, the file buffer path is as follows.
/tmp/fluent/source-only-buffer/{Unique ID for the Fluentd instance}
You can confirm it in the following log output at startup.
[info]: #0 with-source-only: the emitted data will be stored in the buffer files under
/tmp/fluent/source-only-buffer/bbd9006d-bc41-418b-b346-f80888641dda. You can send SIGWINCH to
the supervisor process to cancel with-source-only mode and process data.
This file buffer is the buffer of out_buffer. It works with the default settings of out_buffer except for the following points:
path is automatically determined by default.
overflow_action is drop_oldest_chunk by default.
If needed, you can configure some options for the buffer in System Configuration. Please see the following for details.
If Fluentd stops with the temporary buffer remained, you need to recover the buffer to launch Fluentd with source-only mode again.
Note that a different path will be used each time unless you configure the temporary buffer path explicitly. In this case, you can recover the buffer as follows.
Configure the remaining buffer path explicitly.
Start Fluentd with source-only mode again.
Send SIGWINCH to the supervisor to load the buffer.
If this recovery is necessary, i.e., Fluentd stops with the temporary buffer remained, the following warning log will be displayed. You can confirm the path to configure by this log.
[warn]: #0 some buffer files remain in /tmp/fluent/source-only-buffer/bbd9006d-bc41-418b-b346-f80888641dda.
Please consider recovering or saving the buffer files in the directory. To recover them, you can set
the buffer path manually to system config and retry, i.e., restart Fluentd with with-source-only mode
and send SIGWINCH again. Config Example:
<system>
<source_only_buffer>
path /tmp/fluent/source-only-buffer/bbd9006d-bc41-418b-b346-f80888641dda
</source_only_buffer>
</system>
