Metrics and Logging

Metrics #

The Flink Kubernetes Operator (Operator) extends the Flink Metric System that allows gathering and exposing metrics to centralized monitoring solutions. The well known Metric Reporters are shipped in the operator image and are ready to use.

Slf4j #

The default metrics reporter in the operator is Slf4j. It does not require any external monitoring systems, and it is enabled in the values.yaml file by default, mainly for demonstrating purposes.

  create: true
  append: true
  flink-conf.yaml: |+
    metrics.reporter.slf4j.factory.class: org.apache.flink.metrics.slf4j.Slf4jReporterFactory
    metrics.reporter.slf4j.interval: 5 MINUTE    

To use a more robust production grade monitoring solution the configuration needs to be changed.

How to Enable Prometheus (Example) #

The following example shows how to enable the Prometheus metric reporter:

  create: true
  append: true
  flink-conf.yaml: |+
    metrics.reporter.prom.class: org.apache.flink.metrics.prometheus.PrometheusReporter
    metrics.reporter.prom.port: 9999    

Some metric reporters, including the Prometheus, needs a port to be exposed on the container. This can be achieved be defining a value for the otherwise empty metrics.port variable. Either in the values.yaml file:

  port: 9999

or using the option --set metrics.port=9999 in the command line.

Set up Prometheus locally #

The Prometheus Operator among other options provides an elegant, declarative way to specify how group of pods should be monitored using custom resources.

To install the Prometheus operator via Helm run:

helm repo add prometheus-community
helm install prometheus prometheus-community/kube-prometheus-stack

The Grafana dashboard can be accessed through port-forwarding:

kubectl port-forward deployment/prometheus-grafana 3000

To enable the operator metrics in Prometheus create a pod-monitor.yaml file with the following content:

kind: PodMonitor
  name: flink-kubernetes-operator
    release: prometheus
    matchLabels: flink-kubernetes-operator
      - port: metrics

and apply it on your Kubernetes environment:

kubectl create -f pod-monitor.yaml

Once the custom resource is created in the Kubernetes environment the operator metrics are ready to explore http://localhost:3000/explore.

Logging #

The Operator controls the logging behaviour for Flink applications and the Operator itself using configuration files mounted externally via ConfigMaps. Configuration files with default values are shipped in the Helm chart. It is recommended to review and adjust them if needed in the values.yaml file before deploying the Operator in production environments.

To append/override the default log configuration properties for the Operator use:

  create: true
  append: true |+
        rootLogger.level = DEBUG

Logging in the operator is intentionally succinct and does not include contextual information such as namespace or name of the FlinkDeployment objects. We rely on the MDC provided by the operator-sdk to access this information and use it directly in the log layout.

See the Java Operator SDK docs for more detail.

To append/override the default log configuration properties for Flink applications use:

  create: true
  append: true |+
        rootLogger.level = DEBUG

To learn more about accessing the job logs or changing the log level dynamically check the corresponding section of the core documentation.