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grammatical changes to resource metrics pipeline 

Made some grammatical changes to the text.
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content/en/docs/tasks/debug-application-cluster/resource-metrics-pipeline.md
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@ -9,29 +9,29 @@ content_type: concept
<!-- overview --> <!-- overview -->
Resource usage metrics, such as container CPU and memory usage, Resource usage metrics, such as container CPU and memory usage,
are available in Kubernetes through the Metrics API. These metrics can be either accessed directly are available in Kubernetes through the Metrics API. These metrics can be accessed either directly
by user, for example by using `kubectl top` command, or used by a controller in the cluster, e.g. by the user, i.e. by using the `kubectl top` command, or by a controller in the cluster, e.g.
Horizontal Pod Autoscaler, to make decisions. Horizontal Pod Autoscaler, to make decisions.
<!-- body --> <!-- body -->
## The Metrics API ## The Metrics API
Through the Metrics API you can get the amount of resource currently used Through the Metrics API, you can get the amount of resource currently used
by a given node or a given pod. This API doesn't store the metric values, by a given node or a given pod. This API doesn't store the metric values,
so it's not possible for example to get the amount of resources used by a so it's not possible, for example, to get the amount of resources used by a
given node 10 minutes ago. given node 10 minutes ago.
The API is no different from any other API: The API is no different from any other API:
- it is discoverable through the same endpoint as the other Kubernetes APIs under `/apis/metrics.k8s.io/` path - it is discoverable through the same endpoint as the other Kubernetes APIs under the path: `/apis/metrics.k8s.io/`
- it offers the same security, scalability and reliability guarantees - it offers the same security, scalability, and reliability guarantees
The API is defined in [k8s.io/metrics](https://github.com/kubernetes/metrics/blob/master/pkg/apis/metrics/v1beta1/types.go) The API is defined in [k8s.io/metrics](https://github.com/kubernetes/metrics/blob/master/pkg/apis/metrics/v1beta1/types.go)
repository. You can find more information about the API there. repository. You can find more information about the API there.
{{< note >}} {{< note >}}
The API requires metrics server to be deployed in the cluster. Otherwise it will be not available. The API requires the metrics server to be deployed in the cluster. Otherwise it will be not available.
{{< /note >}} {{< /note >}}
## Measuring Resource Usage ## Measuring Resource Usage
@ -49,20 +49,18 @@ The kubelet chooses the window for the rate calculation.
Memory is reported as the working set, in bytes, at the instant the metric was collected. Memory is reported as the working set, in bytes, at the instant the metric was collected.
In an ideal world, the "working set" is the amount of memory in-use that cannot be freed under memory pressure. In an ideal world, the "working set" is the amount of memory in-use that cannot be freed under memory pressure.
However, calculation of the working set varies by host OS, and generally makes heavy use of heuristics to produce an estimate. However, calculation of the working set varies by host OS, and generally makes heavy use of heuristics to produce an estimate.
It includes all anonymous (non-file-backed) memory since kubernetes does not support swap. It includes all anonymous (non-file-backed) memory since Kubernetes does not support swap.
The metric typically also includes some cached (file-backed) memory, because the host OS cannot always reclaim such pages. The metric typically also includes some cached (file-backed) memory, because the host OS cannot always reclaim such pages.
## Metrics Server ## Metrics Server
[Metrics Server](https://github.com/kubernetes-incubator/metrics-server) is a cluster-wide aggregator of resource usage data. [Metrics Server](https://github.com/kubernetes-incubator/metrics-server) is a cluster-wide aggregator of resource usage data.
It is deployed by default in clusters created by `kube-up.sh` script By default, it is deployed in clusters created by `kube-up.sh` script
as a Deployment object. If you use a different Kubernetes setup mechanism you can deploy it using the provided as a Deployment object. If you use a different Kubernetes setup mechanism, you can deploy it using the provided
[deployment components.yaml](https://github.com/kubernetes-sigs/metrics-server/releases) file. [deployment components.yaml](https://github.com/kubernetes-sigs/metrics-server/releases) file.
Metric server collects metrics from the Summary API, exposed by Metrics Server collects metrics from the Summary API, exposed by
[Kubelet](/docs/reference/command-line-tools-reference/kubelet/) on each node. [Kubelet](/docs/reference/command-line-tools-reference/kubelet/) on each node, and is registered with the main API server via
Metrics Server is registered with the main API server through
[Kubernetes aggregator](/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/). [Kubernetes aggregator](/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/).
Learn more about the metrics server in Learn more about the metrics server in