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Publish Metrics

Publish Metrics

Since version 12.2.1.4 Coherence has had the ability to expose a http endpoint that can be used to scrape metrics. This would typically be used to expose metrics to something like Prometheus.

Note
 The default metrics endpoint is disabled by default in Coherence clusters but can be enabled and configured by setting the relevant fields in the Coherence CRD. If your Coherence version is before CE 21.12.1 this example assumes that your application has included the coherence-metrics module as a dependency. See the Coherence product documentation for more details on enabling metrics in your application.

The example below shows how to enable and access Coherence metrics.

Once the metrics port has been exposed, for example via a load balancer or port-forward command, the metrics endpoint is available at http://host:port/metrics.

See the Using Coherence Metrics documentation for full details on the available metrics.

Important Note Regarding Prometheus Metrics Prefix

From version 3.4.1 of the Coherence Operator, the packaged Grafana dashboards no longer use the vendor: prefix for querying Prometheus metrics. This prefix was deprecated a number of releases ago and the default, of legacy metrics, in Coherence and will be removed in the most recent Coherence releases after this Operator release.

If you are using a Coherence cluster version you are using has not yet changed this property, you may see no metrics in the Grafana dashboards.

To change your cluster to not use legacy names, set the environment variable COHERENCE_METRICS_LEGACY_NAMES to false in your yaml.

metrics-cluster.yaml
apiVersion: coherence.oracle.com/v1
kind: Coherence
metadata:
  name: metrics-cluster
spec:
  env:
    - name: "COHERENCE_METRICS_LEGACY_NAMES"
      value: "false"
  coherence:
...

has not set "coherence.metrics.legacy.names=false"

Deploy Coherence with Metrics Enabled

To deploy a Coherence resource with metrics enabled and exposed on a port, the simplest yaml would look like this:

metrics-cluster.yaml
apiVersion: coherence.oracle.com/v1
kind: Coherence
metadata:
  name: metrics-cluster
spec:
  coherence:
    metrics:
      enabled: true     # (1)
  ports:
    - name: metrics  # (2)

  1. Setting the coherence.metrics.enabled field to true will enable metrics

  2. To expose metrics via a Service it is added to the ports list. The metrics port is a special case where the port number is optional so in this case metrics will bind to the default port 9612. (see Exposing Ports for details)

Expose Metrics on a Different Port

To expose metrics on a different port the alternative port value can be set in the coherence.metrics section, for example:

metrics-cluster.yaml
apiVersion: coherence.oracle.com/v1
kind: Coherence
metadata:
  name: metrics-cluster
spec:
  coherence:
    metrics:
      enabled: true
      port: 8080      # (1)
  ports:
    - name: metrics

  1. metrics will now be exposed on port 8080

Port-forward the Metrics Port

After installing the basic metrics-cluster.yaml from the first example above there would be a three member Coherence cluster installed into Kubernetes.

For example, the cluster can be installed with kubectl

kubectl -n coherence-test create -f metrics-cluster.yaml

coherence.coherence.oracle.com/metrics-cluster created

The kubectl CLI can be used to list Pods for the cluster:

kubectl -n coherence-test get pod -l coherenceCluster=metrics-cluster

NAME                   READY   STATUS    RESTARTS   AGE
metrics-cluster-0   1/1     Running   0          36s
metrics-cluster-1   1/1     Running   0          36s
metrics-cluster-2   1/1     Running   0          36s

In a test or development environment the simplest way to reach an exposed port is to use the kubectl port-forward command. For example to connect to the first Pod in the deployment:

kubectl -n coherence-test port-forward metrics-cluster-0 9612:9612

Forwarding from [::1]:9612 -> 9612
Forwarding from 127.0.0.1:9612 -> 9612

Access the Metrics Endpoint

Now that a port has been forwarded from localhost to a Pod in the cluster the metrics endpoint can be accessed.

Issue the following curl command to access the REST endpoint:

curl http://127.0.0.1:9612/metrics

Prometheus Service Monitor

The operator can create a Prometheus ServiceMonitor for the metrics port so that Prometheus will automatically scrape metrics from the Pods in a Coherence deployment.

metrics-cluster.yaml
apiVersion: coherence.oracle.com/v1
kind: Coherence
metadata:
  name: metrics-cluster
spec:
  coherence:
    metrics:
      enabled: true
  ports:
    - name: metrics
      serviceMonitor:
        enabled: true  # (1)

  1. The serviceMonitor.enabled field is set to true for the metrics port.

See Exposing ports and Services - Service Monitors documentation for more details.