docs: create keptn metrics getting started

docs/content/en/docs/getting-started/metrics/_index.md

@@ -4,3 +4,270 @@ description: Learn how Keptn metrics enhances your deployment
 weight: 25
 ---
 
+The Keptn metrics component of the Keptn Lifecycle Toolkit
+allow you to define any type of metric
+from multiple instances of any type of data source in your Kubernetes cluster.
+You may have tools like Argo, Flux, KEDA, HPA, or Keptn
+that need observability data to make automated decisions.
+Whether a rollout is good, whether to scale up or down.
+Your observability data may come
+from multiple observability solutions --
+Datadog, Dynatrace, Lightstep, Honeycomb, Splunk,
+or data directly from your cloud provider such as AWS, Google, or Azure.
+
+The Keptn Lifecycle Toolkit hooks directly into Kubernetes primitives
+so minimal configuration is required.
+
+The
+[Kubernetes metric server](https://github.com/kubernetes-sigs/metrics-server)
+requires that you maintain point-to-point integrations
+from Argo Rollouts, Flux, KEDA, and HPA.
+Each has plugins but it is difficult to maintain them,
+especially if you are using multiple tools,
+and multible observability platforms,
+and multiple instance of some tools or observability platforms.
+The Keptn Metrics Server unifies and standardizes access to this data.
+
+## Using this exercise
+
+This exercise is based on the
+[simplenode-dev](https://github.com/keptn-sandbox/klt-on-k3s-with-argocd)
+example.
+You can clone that repo to access it locally
+or just look at it for examples
+as you implement the functionality "from scratch"
+on your local Kubernetes deployment cluster.
+
+The steps to implement metrics in an existing cluster are:
+
+1. [Install the Keptn Lifecycle Toolkit](../../install/install)
+1. Configure metrics to use
+   - [Define metrics providers](#define-metrics-providers)
+   - [Define KeptnMetric information](#define-keptnmetric-information)
+   - [View available metrics](#view-available-metrics)
+
+If you want to create your own cluster to run this exercise,
+follow the instructions in [Installation](../../install).
+
+See the
+[Introducing Keptn Lifecycle Toolkit](https://youtu.be/449HAFYkUlY)
+video for a demonstration of this exercise.
+
+## Define metrics to use
+
+You need to define the external observability platforms
+from which you want to pull data
+and then the specific data you want to pull.
+This data is pulled and fetched continuously
+at an interval you specify for each specific bit of data.
+Data is available through the resource and through the data provider itself,
+as well as the Kubernetes CLI.
+
+### Define metrics providers
+
+Populate a
+[KeptnMetricsProvider](../../yaml-crd-ref/metricsprovider.md)
+resource for each external observability platform you want to use.
+
+For our example, we define two observability platforms:
+
+- `dev-prometheus`
+- `dev-dynatrace`
+
+You can specify a virtually unlimited number of providers,
+including multiple instances of each observability platform.
+Each one must be assigned a unique name,
+identified by the type of platform it is
+and the URL.
+
+> Note: The video and example application use an older syntax
+  of the `KeptnMetricsProvider` and `KeptnMetric` resources.
+  The syntax shown in this document is correct for v0.7.1 and later.
+
+Definition of
+[dev-prometheus](https://github.com/keptn-sandbox/klt-on-k3s-with-argocd/blob/main/simplenode-dev/keptn-prometheus-provider.yaml)
+data source:
+
+```yaml
+kind: KeptnMetricsProvider
+metadata:
+  name: dev-prometheus
+  namespace: simplenode-dev
+spec:
+  type: prometheus
+  targetserver: "http://prometheus-k8s-monitoring-svc.cluster.local:9090"
+```
+
+Definition of the
+[dev-dynatrace](https://github.com/keptn-sandbox/klt-on-k3s-with-argocd/blob/main/simplenode-dev/dynatrace-provider.yaml.tmp)
+data source.
+Note that the `dev-dynatrace` server is protected by a secret key
+so that information is included in the provider definition:
+
+```yaml
+kind: KeptnMetricsProvider
+metadata:
+  name: dev-dynatrace
+  namespace: simplenode-dev
+spec:
+  type: dynatrace
+  targetServer: "https://hci34192.live.dynatrace.com"
+  secretKeyRef
+    name: dynatrace
+    key: DT_TOKEN
+...
+```
+
+### Define KeptnMetric information
+
+The [KeptnMetric](../../yaml-crd-ref/metric.md) resource
+defines the information you want to gather,
+specified as a query for the particular observability platform
+you are using.
+You can define any type of metric from any data source.
+
+In our example, we define two bits of information to retrieve:
+
+- Number of CPUs, derived from the `dev-prometheus` data platform
+- `availability` SLO, derived from the `dev-dynatrace` data platform
+
+Each of these are configured to fetch data every 10 seconds
+but you could configure a different `fetchIntervalSeconds` value
+for each metric.
+
+The
+[keptn-metric.yaml](https://github.com/keptn-sandbox/klt-on-k3s-with-argocd/blob/main/simplenode-dev/keptn-metric.yaml)
+file for our example looks like:
+
+```yaml
+apiVersion: metrics.keptn.sh/v1alpha2
+kind: Keptnmetric
+metadata:
+  name: available-cpus
+  namespace: simplenode-dev
+spec:
+  provider:
+    name: dev-prometheus
+  query: "sum(kube_node_status_cvapacity{resources`cpu`})"
+  fetchIntervalSeconds: 10
+...
+apiVersion: metrics.keptn.sh/v1alpha2
+kind: Keptnmetric
+metadata:
+  name: availability-slo
+  namespace: simplenode-dev
+spec:
+  provider:
+    name: dev-dynatrace
+  query: "func:slo.availability_simplenodeservice"
+  fetchIntervalSeconds: 10
+...
+```
+
+Note the following:
+
+- Populate one YAML file per metric
+  then apply all of them.
+- Each metric is assigned a unique `name`.
+- The value of the `spec.provider.name` field
+  must correspond to the name assigned in a
+  the `metadata.name` field of a `KeptnMetricsProvider` resource.
+- Information is fetched in on a continuous basis
+at a rate specified by the value of the `spec.fetchIntervalSeconds` field.
+
+### View available metrics
+
+Use the following command to view
+the metrics that are configured in your cluster.
+This example displays the two metrics we configured above:
+
+```shell
+kubectl get KeptnMetrics -A
+```
+
+```shell
+NAMESPACE       NAME              PROVIDER       QUERY
+simplenode-dev  availability-slo  dev-dynatrace  func:slo.availability_simplenodeservice
+simplenode-dev  available-cpus    dev-prometheus sum(kube_node_status_capacity{resource=`cpu`})
+```
+
+## Run the metrics
+
+As soon as you define your `KeptnMetricsProvider` and `KeptnMetric` resources,
+the Lifecycle Toolkit begins collecting the metrics you defined.
+You do not need to do anything else.
+
+## Observing the metrics
+
+The metrics can be retrieved
+through CRs and through the Kubernetes Metric API.
+
+The syntax to retrieve metrics from the CR is:
+
+```shell
+kubectl get keptnmetrics.metrics.keptn.sh -n <namespace> <metric-name>
+```
+
+For example, the output for the `available-cpus` metric looks like:
+
+```shell
+$ kubectl get keptnmetrics.metrics.keptn.sh -n simplenode-dev available-cpus
+
+NAME             PROVIDER     QUERY                                           VALUE
+cpu-throttling   my-provider  sum(kube_node_status_capacity{resource=`cpu`})   6.000
+```
+
+The syntax to retrieve metrics through the Kubernetes API  is:
+
+```yaml
+kubectl get --raw "/apis/custom.metrics.k8s.io/v1beta2/namespaces/<namespace>/keptnmetrics.metrics.sh/<metric-name>/<metric-name>"
+```
+
+For example, the output for the `available-cpus` looks like:
+
+```yaml
+$ kubectl get --raw "/apis/custom.metrics.k8s.io/v1beta2/namespaces/simplenode-dev/keptnmetrics.metrics.sh/available-cpus/available-cpus"
+
+{
+  "kind": "MetricValueList",
+  "apiVersion": "custom.metrics.k8s.io/v1beta2",
+  "metadata": {},
+  "items": [
+    {
+      "describedObject": {
+        "kind": "KeptnMetric",
+        "namespace": "simplenode-dev",
+        "name": "available-cpus",
+        "apiVersion": "metrics.keptn.sh/v1alpha2"
+      },
+      "metric": {
+        "name": "available-cpus",
+        "selector": {}
+      },
+      "timestamp": "2023-05-11T08:05:36Z",
+      "value": "6"
+    }
+  ]
+}
+```
+
+You can also display the graphics using a dashboard such as Grafana.
+
+## Implementing autoscaling with HPA
+
+The Kubernetes HorizontalPodAutoscaler (HPA)
+uses metrics to provide autoscaling for the cluster.
+HPA can retrieve KeptnMetrics and use it to implement HPA.
+See Using the [HorizontalPodAutoscaler](../../implmenting/evaluatemetrics)
+for detailed information.
+
+TODO: Link to HPA subsection after that content is merged
+
+## Learn more
+
+To learn more about the Keptn Metrics Server, see:
+
+- Architecture:
+  [Keptn Metrics Operator](../../concepts/architecture/components/metrics-operator/)
+- More information about implementing Keptn Metrics:
+  [Keptn Metrics](../../implementing/evaluatemetrics.md/)