Understanding cluster logging

You can use JSON logging to configure the Log Forwarding API to parse JSON strings into a structured object. You can perform the following tasks:

For information, see About JSON logging.

The OKD Event Router is a pod that watches Kubernetes events and logs them for collection by OKD logging. You must manually deploy the Event Router.

For information, see About collecting and storing Kubernetes events.

OKD allows you to update OKD logging. You must update the following operators while updating OKD logging:

For information, see About updating OKD logging.

The OKD logging dashboard contains charts that show details about your Elasticsearch instance at the cluster level. These charts help you diagnose and anticipate problems.

For information, see About viewing the cluster dashboard.

You can troubleshoot the logging issues by performing the following tasks:

You can stop log aggregation by deleting the Clusterlogging custom resource (CR). After deleting the CR, there are other cluster logging components that remain, which you can optionally remove.

For information, see About uninstalling OKD logging.

The logging system exports fields. Exported fields are present in the log records and are available for searching from Elasticsearch and Kibana.

For information, see About exporting fields.

The cluster logging components include a collector deployed to each node in the OKD cluster that collects all node and container logs and writes them to a log store. You can use a centralized web UI to create rich visualizations and dashboards with the aggregated data.

The major components of cluster logging are:

This document might refer to log store or Elasticsearch, visualization or Kibana, collection or Fluentd, interchangeably, except where noted.

OKD uses Fluentd to collect container and node logs.

By default, the log collector uses the following sources:

The logging collector is deployed as a daemon set that deploys pods to each OKD node. System and infrastructure logs are generated by journald log messages from the operating system, the container runtime, and OKD. Application logs are generated by the CRI-O container engine. Fluentd collects the logs from these sources and forwards them internally or externally as you configure in OKD.

The container runtimes provide minimal information to identify the source of log messages: project, pod name, and container id. This is not sufficient to uniquely identify the source of the logs. If a pod with a given name and project is deleted before the log collector begins processing its logs, information from the API server, such as labels and annotations, might not be available. There might not be a way to distinguish the log messages from a similarly named pod and project or trace the logs to their source. This limitation means log collection and normalization is considered best effort.

For information, see Configuring the log collector.

By default, OKD uses Elasticsearch (ES) to store log data. Optionally, you can use the log forwarding features to forward logs to external log stores using Fluentd protocols, syslog protocols, or the OKD Log Forwarding API.

The cluster logging Elasticsearch instance is optimized and tested for short term storage, approximately seven days. If you want to retain your logs over a longer term, it is recommended you move the data to a third-party storage system.

Elasticsearch organizes the log data from Fluentd into datastores, or indices, then subdivides each index into multiple pieces called shards, which it spreads across a set of Elasticsearch nodes in an Elasticsearch cluster. You can configure Elasticsearch to make copies of the shards, called replicas, which Elasticsearch also spreads across the Elasticsearch nodes. The Clusterlogging custom resource (CR) allows you to specify how the shards are replicated to provide data redundancy and resilience to failure. You can also specify how long the different types of logs are retained using a retention policy in the Clusterlogging CR.

The Cluster logging Operator and companion OpenShift Elasticsearch Operator ensure that each Elasticsearch node is deployed using a unique deployment that includes its own storage volume. You can use a Clusterlogging custom resource (CR) to increase the number of Elasticsearch nodes, as needed. Refer to the Elasticsearch documentation for considerations involved in configuring storage.

Role-based access control (RBAC) applied on the Elasticsearch indices enables the controlled access of the logs to the developers. Administrators can access all logs and developers can access only the logs in their projects.

For information, see Configuring the log store.

OKD uses Kibana to display the log data collected by Fluentd and indexed by Elasticsearch.

Kibana is a browser-based console interface to query, discover, and visualize your Elasticsearch data through histograms, line graphs, pie charts, and other visualizations.

For information, see Configuring the log visualizer.

The Event Router is a pod that watches OKD events so they can be collected by cluster logging. The Event Router collects events from all projects and writes them to STDOUT. Fluentd collects those events and forwards them into the OKD Elasticsearch instance. Elasticsearch indexes the events to the infra index.

You must manually deploy the Event Router.

For information, see Collecting and storing Kubernetes events.

By default, OKD cluster logging sends logs to the default internal Elasticsearch log store, defined in the Clusterlogging custom resource (CR). If you want to forward logs to other log aggregators, you can use the log forwarding features to send logs to specific endpoints within or outside your cluster.

For information, see Forwarding logs to third party systems.