Setting up a logging plugin

Knative allows cluster operators to use different backends for their logging needs. This document describes how to change these settings. Knative currently requires changes in Fluentd configuration files, however we plan on abstracting logging configuration in the future (#906). Once #906 is complete, the methodology described in this document will no longer be valid and migration to a new process will be required. In order to minimize the effort for a future migration, we recommend only changing the output configuration of Fluentd and leaving the rest intact.

NOTE: All the files mentioned below are in knative/serving repository. You run the commands mentioned below from the root directory of knative/serving.


Configure the DaemonSet for stdout/stderr logs

Operators can do the following steps to configure the Fluentd DaemonSet for collecting stdout/stderr logs from the containers:

  1. Replace 900.output.conf part in 100-fluentd-configmap.yaml with the desired output configuration. Knative provides a sample for sending logs to Elasticsearch or Stackdriver. Developers can simply use 100-fluentd-configmap.yaml or override any with other configuration.
  2. Replace the image field of fluentd-ds container of fluentd-ds DaemonSet in 200-fluentd.yaml with the Fluentd image including the desired Fluentd output plugin. See here for the requirements of Flunetd image on Knative.

Configure the Sidecar for log files under /var/log

Currently operators have to configure the Fluentd Sidecar separately for collecting log files under /var/log. An effort is in process to get rid of the sidecar. The steps to configure are:

  1. Replace logging.fluentd-sidecar-output-config flag in config-observability with the desired output configuration. NOTE: The Fluentd DaemonSet is in monitoring namespace while the Fluentd sidecar is in the namespace same with the app. There may be small differences between the configuration for DaemonSet and sidecar even though the desired backends are the same.
  2. Replace logging.fluentd-sidecar-image flag in config-observability with the Fluentd image including the desired Fluentd output plugin. In theory, this is the same with the one for Fluentd DaemonSet.


Operators need to deploy Knative components after the configuring:

# Deploy the configuration for sidecar
kubectl apply --filename config/config-observability.yaml

# Deploy the DaemonSet to make configuration for DaemonSet take effect
kubectl apply --recursive --filename config/monitoring/100-namespace.yaml \
    --filename <path-of-fluentd-daemonset-config>

In the commands above, replace <path-of-fluentd-daemonset-config> with the Fluentd DaemonSet configuration file, e.g. config/monitoring/logging/stackdriver.

NOTE: The deployment above will not affect the fluentd sidecar of existing pods. Developers need to redeploy their app to get the newest configuration for the fluentd sidecar used to send logs to /var/log.

NOTE: Operators sometimes need to deploy extra services as the logging backends. For example, if they desire Elasticsearch&Kibana, they have to deploy the Elasticsearch and Kibana services. Knative provides this sample:

kubectl apply --recursive --filename third_party/config/monitoring/logging/elasticsearch

See here for deploying the whole Knative monitoring components.


To uninstall a logging plugin, run:

kubectl delete --recursive --filename <path-of-fluentd-daemonset-config>

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