Add documentation for default metrics exported by Istio (#1485) (#1542)

.spelling

@@ -252,6 +252,7 @@ destination.port
 destination.service
 destination.uid
 destination.user
+details.default.svc.cluster.local
 dev
 dm_bookinfo.png
 dm_gcp_iam.png
@@ -468,6 +469,7 @@ response.headers
 response.size
 response.time
 reviews.abc.svc.cluster.local
+reviews.default.svc.cluster.local
 roadmap
 roleRef
 roles_summary.png

content/docs/reference/config/policy-and-telemetry/metrics.md

@@ -0,0 +1,88 @@
+---
+title: Default Metrics
+description: Default Metrics exported from Istio through Mixer.
+weight: 50
+---
+
+This page presents details about the metrics that Istio collects when using its initial configuration. You can add and remove metrics by changing configuration at any time, but this is the built-in set. They can be found
+[here](https://github.com/istio/istio/blob/{{<branch_name>}}/install/kubernetes/helm/istio/charts/mixer/templates/config.yaml)
+under the section with “kind: metric”. It uses [metric
+template](/docs/reference/config/policy-and-telemetry/templates/metric/) to define these metrics.
+
+We will describe metrics first and then the labels for each metric.
+
+## Metrics
+
+*   **Request Count**: This is a `COUNTER`
+    [metric](https://github.com/istio/istio/blob/{{<branch_name>}}/install/kubernetes/templates/istio-mixer.yaml.tmpl#L786:9)
+    incremented for every request handled by an Istio proxy.
+
+*   **Request Duration**: This is a `DISTRIBUTION`
+    [metric](https://github.com/istio/istio/blob/{{<branch_name>}}/install/kubernetes/templates/istio-mixer.yaml.tmpl#L802:9)
+    which measures the duration of the request (as observed by the server-side
+    proxy).
+
+*   **Request Size**: This is a `DISTRIBUTION`
+    [metric](https://github.com/istio/istio/blob/{{<branch_name>}}/install/kubernetes/templates/istio-mixer.yaml.tmpl#L818:9)
+    which measures the size of the HTTP request’s body size.
+
+*   **Response Size**: This is a `DISTRIBUTION`
+    [metric](https://github.com/istio/istio/blob/{{<branch_name>}}/install/kubernetes/templates/istio-mixer.yaml.tmpl#L834:9)
+    which measures the size of the HTTP response body size.
+
+*   **Tcp Byte Sent**: This is a `COUNTER`
+    [metric](https://github.com/istio/istio/blob/{{<branch_name>}}/install/kubernetes/templates/istio-mixer.yaml.tmpl#L850:9)
+    which measures the size of total bytes sent during response in case of a TCP
+    connection as measured by the server-side proxy.
+
+*   **Tcp Byte Received**: This is a `COUNTER`
+    [metric](https://github.com/istio/istio/blob/{{<branch_name>}}/install/kubernetes/templates/istio-mixer.yaml.tmpl#L867:9)
+    which measures the size of total bytes received during request in case of a
+    TCP connection as measured by the server-side proxy.
+
+## Labels
+
+*   **Source Service**: This identifies the source service responsible for an
+    incoming request. This is also the FQDN for a source service. Ex:
+    "reviews.default.svc.cluster.local".
+
+    ```yaml
+    source_service: source.service | "unknown"
+    ```
+
+*   **Source Version**: This identifies the version of the source service of the
+    request.
+
+    ```yaml
+    source_version: source.labels["version"] | "unknown"
+    ```
+
+*   **Destination Service**: This identifies the destination service responsible
+    for an incoming request. This is also the FQDN for a source service. Ex:
+    "details.default.svc.cluster.local".
+
+    ```yaml
+    destination_service: destination.service | "unknown"
+    ```
+
+*   **Destination Version**: This identifies the version of the source service
+    of the request.
+
+    ```yaml
+    destination_version: destination.labels["version"] | "unknown"
+    ```
+
+*   **Response Code**: This identifies the response code of the request. This
+    label is present only on HTTP metrics.
+
+    ```yaml
+    response_code: response.code | 200
+    ```
+
+*   **Connection mTLS**: This identifies the service authentication policy of
+    the request. It is set to true, when istio is used to make secure
+    communications.
+
+    ```yaml
+    connection_mtls: connection.mtls | false
+    ```