How to configure the logging app to use Custom PVC volume for Fluentd buffers

This document (000020976) is provided subject to the disclaimer at the end of this document.

Environment

Rancher with Rancher-Logging chart v2

Resolution

Go to Apps > Charts, then Select Logging and click Install/Update
Select the project to install the logging app and select "Customize Helm Options before install", and click Next
Select Edit YAML tab and modify the following:

Search for disablePvc and change that from true to false

disablePvc: false

Search for the bufferStorageVolume section and change it to the following (Modify the STORAGE_CLASS_NAME with your environement value):

  bufferStorageVolume:
    pvc:
      spec:
        accessModes:
          - ReadWriteOnce
        resources:
          requests:
            storage: 40Gi
        storageClassName: "<STORAGE_CLASS_NAME>"
        volumeMode: Filesystem

Modify other fields if required, and finally, Click on Next, then Install/Update.

If the logging app is already installed, then the PVC will need to be created manually and associated with the fluentd StatefulSet, as per the following steps:

From UI go to Storage > PersistentVolumeClaims, and Create PVC to be used for the fluentd pod (PVC need to be on the namespace cattle-logging-system):

> kubectl get pvc -n cattle-logging-system
NAME                                  STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS            AGE
rancher-logging-root-fluentd-buffer   Bound    pvc-4b78c686-7b68-4f7d-a40f-32c0a5470831   40Gi       RWO            rancher-storage-class   10s

From UI, go to Workload > StatefulSets, then Edit the fluentd StatefulSet YAML (rancher-logging-root-fluentd) and update the claimName for the rancher-logging-root-fluentd-buffer volume with the PVC name.

Change the following two lines:

      - emptyDir: {}
        name: rancher-logging-root-fluentd-buffer

To the following:

      - name: rancher-logging-root-fluentd-buffer
        persistentVolumeClaim:
          claimName: "rancher-logging-root-fluentd-buffer"

Finally, click on save, and a new fluentd pod will be scheduled with to use PV for buffer volume.

To confirm if fluentd is using PV for buffer volume, you can run the following command and review the mount and volumes output sections:

kubectl describe pod rancher-logging-root-fluentd-0 -n cattle-logging-system

If fluentd is using PV for buffer volume, the output will be:

  rancher-logging-root-fluentd-buffer:
    Type:       PersistentVolumeClaim (a reference to a PersistentVolumeClaim in the same namespace)
    ClaimName:  rancher-logging-root-fluentd-buffer
    ReadOnly:   false

If fluentd is using EmptyDir for buffer volume, the output will be:

  rancher-logging-root-fluentd-buffer:
    Type:       EmptyDir (a temporary directory that shares a pod's lifetime)
    Medium:     
    SizeLimit:  <unset>

Reference:

https://banzaicloud.com/docs/one-eye/logging-operator/logging-infrastructure/fluentd/

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