If the Fluentd log collector is unable to keep up with a high number of logs,
Fluentd performs file buffering to reduce memory usage and prevent data loss.
Fluentd file buffering stores records in chunks. Chunks are stored in buffers.
You can tune file buffering in your cluster by editing environment variables
in the Fluentd daemon set:
To modify the
in the Fluentd daemon set, you must set cluster logging to the unmanaged state.
Operators in an unmanaged state are unsupported and the cluster administrator
assumes full control of the individual component configurations and upgrades.
BUFFER_SIZE_LIMIT. This parameter determines the maximum size of each chunk
file before Fluentd creates a new chunk. The default is
This parameter sets the Fluentd
BUFFER_SIZE_LIMIT can collect more records per chunk file. However,
bigger records take longer to be sent to the logstore.
FILE_BUFFER_LIMIT. This parameter determines the file buffer size per logging output.
This value is only a request based on the available space on the node where a Fluentd pod is scheduled.
OpenShift Container Platform does not allow Fluentd to exceed the node capacity. The default is
FILE_BUFFER_LIMIT could translate to a higher
BUFFER_QUEUE_LIMIT based the number of outputs.
However, if the node’s space is under pressure, Fluentd can fail.
By default, the
1 if all the logs are sent to a single resource, and is incremented by
1 for each
additional resource. You might have multiple outputs if you use the Log Forwarding API, the Fluentd Forward protocol, or
syslog protocol to forward logs to external locations.
The permanent volume size must be larger than
FILE_BUFFER_LIMIT multiplied by the
number of outputs.
BUFFER_QUEUE_LIMIT. This parameter is the maximum number of buffer chunks allowed.
BUFFER_QUEUE_LIMIT parameter is not directly tunable. OpenShift Container Platform calculates this value
based on the number of logging outputs, the chunk size, and the filesystem space available.
The default is
32 chunks. To change the
BUFFER_QUEUE_LIMIT, you must change the value of
BUFFER_QUEUE_LIMIT parameter sets the Fluentd
OpenShift Container Platform calculates the
(FILE_BUFFER_LIMIT / (number_of_outputs * BUFFER_SIZE_LIMIT)).
Using the default set of values, the value of
BUFFER_QUEUE_LIMIT is 32:
OpenShift Container Platform uses the Fluentd file buffer plug-in
to configure how the chunks are stored. You can see the location of the buffer file
using the following command:
$ oc get cm fluentd -o json | jq -r '.data."fluent.conf"'
@type file (1)
path '/var/lib/flunetd/retry-elasticsearch' (2)
|The Fluentd file buffer plugin. Do not change this value.
|The path where buffer chunks are stored.
To configure Buffer Chunk Limiting:
Edit either of the following parameters in the
fluentd daemon set.
- name: FILE_BUFFER_LIMIT (1)
- name: BUFFER_SIZE_LIMIT (2)
|Specify the Fluentd file buffer size per output.
|Specify the maximum size of each Fluentd buffer chunk.