You can configure the Fluentd deployment via the fluentd section of the Logging custom resource. This page shows some examples on configuring Fluentd. For the detailed list of available parameters, see FluentdSpec.

Custom pvc volume for Fluentd buffers 🔗︎

apiVersion: logging.banzaicloud.io/v1beta1
kind: Logging
metadata:
  name: default-logging-simple
spec:
  fluentd:
    bufferStorageVolume:
      pvc:
        spec:
          accessModes:
            - ReadWriteOnce
          resources:
            requests:
              storage: 40Gi
          storageClassName: fast
          volumeMode: Filesystem
  fluentbit: {}
  controlNamespace: logging

Custom Fluentd hostPath volume for buffers 🔗︎

apiVersion: logging.banzaicloud.io/v1beta1
kind: Logging
metadata:
  name: default-logging-simple
spec:
  fluentd:
    disablePvc: true
    bufferStorageVolume:
      hostPath:
        path: "" # leave it empty to automatically generate: /opt/logging-operator/default-logging-simple/default-logging-simple-fluentd-buffer
  fluentbit: {}
  controlNamespace: logging

FluentOutLogrotate 🔗︎

The following snippet redirects Fluentd’s stdout to a file and configures rotation settings.

This is important to avoid Fluentd getting into a ripple effect when there is an error and the error message gets back to the system as a log message, which generates another error, and so on.

Default settings configured by the operator:

spec:
  fluentd:
    fluentOutLogrotate:
      enabled: true
      path: /fluentd/log/out
      age: 10
      size: 10485760

Disabling it and write to stdout (not recommended):

spec:
  fluentd:
    fluentOutLogrotate:
      enabled: false

Scaling 🔗︎

You can scale the Fluentd deployment manually by changing the number of replicas in the fluentd section of the Logging custom resource. For example:

apiVersion: logging.banzaicloud.io/v1beta1
kind: Logging
metadata:
  name: default-logging-simple
spec:
  fluentd:
    scaling:
      replicas: 3
  fluentbit: {}
  controlNamespace: logging

For automatic scaling, see Autoscaling with HPA.

Graceful draining 🔗︎

While you can scale down the Fluentd deployment by decreasing the number of replicas in the fluentd section of the Logging custom resource, it won’t automatically be graceful, as the controller will stop the extra replica pods without waiting for any remaining buffers to be flushed. You can enable graceful draining in the scaling subsection:

apiVersion: logging.banzaicloud.io/v1beta1
kind: Logging
metadata:
  name: default-logging-simple
spec:
  fluentd:
    scaling:
      drain:
        enabled: true
  fluentbit: {}
  controlNamespace: logging

When graceful draining is enabled, the operator starts drainer jobs for any undrained volumes. The drainer job flushes any remaining buffers before terminating, and the operator marks the associated volume (the PVC, actually) as drained until it gets used again. The drainer job has a template very similar to that of the Fluentd deployment with the addition of a sidecar container that oversees the buffers and signals Fluentd to terminate when all buffers are gone. Pods created by the job are labeled as not to receive any further logs, thus buffers will clear out eventually.

If you want, you can specify a custom drainer job sidecar image in the drain subsection:

apiVersion: logging.banzaicloud.io/v1beta1
kind: Logging
metadata:
  name: default-logging-simple
spec:
  fluentd:
    scaling:
      drain:
        enabled: true
        image:
          repository: ghcr.io/banzaicloud/fluentd-drain-watch
          tag: latest
  fluentbit: {}
  controlNamespace: logging

In addition to the drainer job, the operator also creates a placeholder pod with the same name as the terminated pod of the Fluentd deployment to keep the deployment from recreating that pod which would result in concurrent access of the volume. The placeholder pod just runs a pause container, and goes away as soon as the job has finished successfully or the deployment is scaled back up and explicitly flushing the buffers is no longer necessary because the newly created replica will take care of processing them.

You can mark volumes that should be ignored by the drain logic by adding the label logging.banzaicloud.io/drain: no to the PVC.

Autoscaling with HPA 🔗︎

To configure autoscaling of the Fluentd deployment using Horizontal Pod Autoscaler (HPA), complete the following steps.

  1. Configure the aggregation layer. Many providers already have this configured, including kind.

  2. Install Prometheus and the Prometheus Adapter if you don’t already have them installed on the cluster. Adjust the default Prometheus address values as needed for your environment (set prometheus.url, prometheus.port, and prometheus.path to the appropriate values).

  3. (Optional) Install metrics-server to access basic metrics. If the readiness of the metrics-server pod fails with HTTP 500, try adding the --kubelet-insecure-tls flag to the container.

  4. If you want to use a custom metric for autoscaling Fluentd and the necessary metric is not available in Prometheus, define a Prometheus recording rule:

    groups:
    - name: my-logging-hpa.rules
      rules:
      - expr: (node_filesystem_size_bytes{container="buffer-metrics-sidecar",mountpoint="/buffers"}-node_filesystem_free_bytes{container="buffer-metrics-sidecar",mountpoint="/buffers"})/node_filesystem_size_bytes{container="buffer-metrics-sidecar",mountpoint="/buffers"}
        record: buffer_space_usage_ratio
    

    Alternatively, you can define the derived metric as a configuration rule in the Prometheus Adapter’s config map.

  5. If it’s not already installed, install the logging-operator and configure a logging resource with at least one flow. Make sure that the logging resource has buffer volume metrics monitoring enabled under spec.fluentd:

    #spec:
    #  fluentd:
        bufferVolumeMetrics:
          serviceMonitor: true
    
  6. Verify that the custom metric is available by running:

    kubectl get --raw '/apis/custom.metrics.k8s.io/v1beta1/namespaces/default/pods/*/buffer_space_usage_ratio'
    
  7. The logging-operator enforces the replica count of the stateful set based on the logging resource’s replica count, even if it’s not set explicitly. To allow for HPA to control the replica count of the stateful set, this coupling has to be severed. Currently, the only way to do that is by deleting the logging-operator deployment.

  8. Create a HPA resource. The following example tries to keep the average buffer volume usage of Fluentd instances at 80%.

    apiVersion: autoscaling/v2beta2
    kind: HorizontalPodAutoscaler
    metadata:
      name: one-eye-fluentd
    spec:
      scaleTargetRef:
        apiVersion: apps/v1
        kind: StatefulSet
        name: one-eye-fluentd
      minReplicas: 1
      maxReplicas: 10
      metrics:
      - type: Pods
        pods:
          metric:
            name: buffer_space_usage_ratio
          target:
            type: AverageValue
            averageValue: 800m
    

Probe 🔗︎

A Probe is a diagnostic performed periodically by the kubelet on a Container. To perform a diagnostic, the kubelet calls a Handler implemented by the Container. You can configure a probe for Fluentd in the livenessProbe section of the Logging custom resource. For example:

apiVersion: logging.banzaicloud.io/v1beta1
kind: Logging
metadata:
  name: default-logging-simple
spec:
  fluentd:
    livenessProbe:
      periodSeconds: 60
      initialDelaySeconds: 600
      exec:
        command:
        - "/bin/sh"
        - "-c"
        - >
          LIVENESS_THRESHOLD_SECONDS=${LIVENESS_THRESHOLD_SECONDS:-300};
          if [ ! -e /buffers ];
          then
            exit 1;
          fi;
          touch -d "${LIVENESS_THRESHOLD_SECONDS} seconds ago" /tmp/marker-liveness;
          if [ -z "$(find /buffers -type d -newer /tmp/marker-liveness -print -quit)" ];
          then
            exit 1;
          fi;
  fluentbit: {}
  controlNamespace: logging

You can use the following parameters:

Name Type Default Description
initialDelaySeconds int 0 Number of seconds after the container has started before liveness probes are initiated.
timeoutSeconds int 1 Number of seconds after which the probe times out.
periodSeconds int 10 How often (in seconds) to perform the probe.
successThreshold int 1 Minimum consecutive successes for the probe to be considered successful after having failed.
failureThreshold int 3 Minimum consecutive failures for the probe to be considered failed after having succeeded.
exec array {} Exec specifies the action to take. More info
httpGet array {} HTTPGet specifies the http request to perform. More info
tcpSocket array {} TCPSocket specifies an action involving a TCP port. More info

Custom Fluentd image 🔗︎

You can deploy custom images by overriding the default images using the following parameters in the fluentd or fluentbit sections of the logging resource.

Name Type Default Description
repository string "” Image repository
tag string "” Image tag
pullPolicy string "” Always, IfNotPresent, Never

The following example deploys a custom fluentd image:

apiVersion: logging.banzaicloud.io/v1beta1
kind: Logging
metadata:
  name: default-logging-simple
spec:
  fluentd:
    image:
      repository: banzaicloud/fluentd
      tag: v1.10.4-alpine-1
      pullPolicy: IfNotPresent
    configReloaderImage:
      repository: jimmidyson/configmap-reload
      tag: v0.4.0
      pullPolicy: IfNotPresent
    scaling:
      drain:
        image:
          repository: ghcr.io/banzaicloud/fluentd-drain-watch
          tag: v0.0.1
          pullPolicy: IfNotPresent
    bufferVolumeImage:
      repository: quay.io/prometheus/node-exporter
      tag: v1.1.2
      pullPolicy: IfNotPresent
  fluentbit: {}
  controlNamespace: logging

KubernetesStorage 🔗︎

Define Kubernetes storage.

Name Type Default Description
hostPath HostPathVolumeSource - Represents a host path mapped into a pod. If path is empty, it will automatically be set to “/opt/logging-operator//” 
emptyDir EmptyDirVolumeSource - Represents an empty directory for a pod. 
pvc PersistentVolumeClaim - A PersistentVolumeClaim (PVC) is a request for storage by a user. 

Persistent Volume Claim 🔗︎

Name Type Default Description
spec PersistentVolumeClaimSpec - Spec defines the desired characteristics of a volume requested by a pod author. 
source PersistentVolumeClaimVolumeSource - PersistentVolumeClaimVolumeSource references the user’s PVC in the same namespace.  

The Persistent Volume Claim should be created with the given spec and with the name defined in the source's claimName.