[enterprise-4.6] SRVKS-573: Autoscaling docs improvements

_topic_maps/_topic_map.yml

@@ -2707,11 +2707,7 @@ Topics:
   - Name: Serverless applications
     File: serverless-applications
   - Name: Autoscaling
-    File: serverless-autoscaling
-  - Name: Scale bounds
-    File: serverless-autoscaling-scale-bounds
-  - Name: Concurrency
-    File: serverless-autoscaling-concurrency
+    File: serverless-autoscaling-developer
   - Name: Traffic management
     File: serverless-traffic-management
   - Name: Routing
@@ -2749,6 +2745,8 @@ Topics:
     File: serverless-cluster-admin-serving
   - Name: Configuring the Knative Serving custom resource
     File: knative-serving-CR-config
+  - Name: Autoscaling
+    File: serverless-admin-autoscaling
     # Ingress options
   - Name: Integrating Service Mesh with OpenShift Serverless
     File: serverless-ossm-setup

modules/serverless-autoscaling-minscale-kn.adoc

@@ -11,12 +11,12 @@ You can use the `kn service` command with the `--min-scale` flag to create or mo
 
 * Set the minimum number of replicas for the service by using the `--min-scale` flag:
 +
-.Examples
 [source,terminal]
 ----
 $ kn service create <service_name> --image <image_uri> --min-scale <integer>
 ----
 +
+.Example command
 [source,terminal]
 ----
 $ kn service create example-service --image quay.io/openshift-knative/knative-eventing-sources-event-display:latest --min-scale 2

modules/serverless-enable-scale-to-zero.adoc

@@ -0,0 +1,31 @@
+// Module included in the following assemblies:
+//
+// * serverless/admin_guide/serverless-admin-autoscaling.adoc
+
+[id="serverless-enable-scale-to-zero_{context}"]
+= Enabling scale-to-zero
+
+Cluster administrators can enable or disable scale-to-zero globally for the cluster.
+
+.Prerequisites
+
+* You have installed {ServerlessOperatorName} and Knative Serving on your cluster.
+* You have cluster administrator permissions.
+* You are using the default Knative Pod Autoscaler. The scale to zero feature is not available if you are using the Kubernetes Horizontal Pod Autoscaler.
+
+.Procedure
+
+* Modify the `enable-scale-to-zero` spec in the `KnativeServing` CR:
++
+[source,yaml]
+----
+apiVersion: operator.knative.dev/v1alpha1
+kind: KnativeServing
+metadata:
+  name: knative-serving
+spec:
+  config:
+    autoscaler:
+      enable-scale-to-zero: "false" <1>
+----
+<1> The `enable-scale-to-zero` spec can be either `"true"` or `"false"`. If set to true, scale-to-zero is enabled. If set to false, applications are scaled down to the configured _minimum scale bound_. The default value is `"true"`.

modules/serverless-scale-to-zero-grace-period.adoc

@@ -0,0 +1,31 @@
+// Module included in the following assemblies:
+//
+// * serverless/admin_guide/serverless-admin-autoscaling.adoc
+
+[id="serverless-scale-to-zero-grace-period_{context}"]
+= Configuring the scale-to-zero grace period
+
+This setting specifies an upper bound time limit that Knative waits for scale-from-zero machinery to be in place before the last replica of an application is removed.
+
+.Prerequisites
+
+* You have installed {ServerlessOperatorName} and Knative Serving on your cluster.
+* You have cluster administrator permissions.
+* You are using the default Knative Pod Autoscaler. The scale to zero feature is not available if you are using the Kubernetes Horizontal Pod Autoscaler.
+
+.Procedure
+
+* Modify the `scale-to-zero-grace-period` spec in the `KnativeServing` CR:
++
+[source,yaml]
+----
+apiVersion: operator.knative.dev/v1alpha1
+kind: KnativeServing
+metadata:
+  name: knative-serving
+spec:
+  config:
+    autoscaler:
+      scale-to-zero-grace-period: "30s" <1>
+----
+<1> The grace period time in seconds. The default value is 30 seconds.

serverless/admin_guide/serverless-admin-autoscaling.adoc

@@ -0,0 +1,12 @@
+[id="serverless-admin-autoscaling"]
+= Autoscaling
+include::modules/common-attributes.adoc[]
+include::modules/serverless-document-attributes.adoc[]
+:context: serverless-admin-autoscaling
+
+toc::[]
+
+As a cluster administrator, you can set global and per-namespace default configurations for autoscaling features by modifying the `KnativeServing` custom resource (CR). This propagates changes to the relevant config maps.
+
+include::modules/serverless-enable-scale-to-zero.adoc[leveloffset=+1]
+include::modules/serverless-scale-to-zero-grace-period.adoc[leveloffset=+1]

serverless/develop/serverless-autoscaling-developer.adoc

@@ -0,0 +1,98 @@
+[id="serverless-autoscaling-developer"]
+= Autoscaling
+include::modules/common-attributes.adoc[]
+include::modules/serverless-document-attributes.adoc[]
+:context: serverless-autoscaling-developer
+
+toc::[]
+
+Knative Serving provides automatic scaling, or _autoscaling_, for applications to match incoming demand. For example, if an application is receiving no traffic, and scale-to-zero is enabled, Knative Serving scales the application down to zero replicas. If scale-to-zero is disabled, the application is scaled down to the xref:../../serverless/develop/serverless-autoscaling-developer.adoc#serverless-autoscaling-developer-minscale[minimum number of replicas specified for applications on the cluster]. Replicas can also be scaled up to meet demand if traffic to the application increases.
+
+If Knative autoscaling is enabled for your cluster, you can configure concurrency and scale bounds for your application.
+
+[NOTE]
+====
+Any limits or targets set in the revision template are measured against a single instance of your application. For example, setting the `target` annotation to `50` configures the autoscaler to scale the application so that each revision handles 50 requests at a time.
+====
+
+[id="serverless-autoscaling-developer-scale-bounds"]
+== Scale bounds
+
+Scale bounds determine the minimum and maximum numbers of replicas that can serve an application at any given time.
+
+You can set scale bounds for an application to help prevent cold starts or control computing costs.
+
+[id="serverless-autoscaling-developer-minscale"]
+=== Minimum scale bounds
+
+The minimum number of replicas that can serve an application is determined by the `minScale` annotation.
+
+The `minScale` value defaults to `0` replicas if the following conditions are met:
+
+* The `minScale` annotation is not set
+* Scaling to zero is enabled
+* The class `KPA` is used
+
+If scale to zero is not enabled, the `minScale` value defaults to `1`.
+
+// TODO: Document KPA if supported, link to docs about setting class
+
+// TO DO:
+// Add info / links about enabling and disabling autoscaling (admin docs)
+// if `enable-scale-to-zero` is set to `false` in the `config-autoscaler` config map.
+
+.Example service spec with `minScale` spec
+[source,yaml]
+----
+apiVersion: serving.knative.dev/v1
+kind: Service
+metadata:
+  name: example-service
+  namespace: default
+spec:
+  template:
+    metadata:
+      annotations:
+        autoscaling.knative.dev/minScale: "0"
+...
+----
+
+include::modules/serverless-autoscaling-minscale-kn.adoc[leveloffset=+3]
+
+[id="serverless-autoscaling-developer-maxscale"]
+=== Maximum scale bounds
+
+The maximum number of replicas that can serve an application is determined by the `maxScale` annotation. If the `maxScale` annotation is not set, there is no upper limit for the number of replicas created.
+
+.Example service spec with `maxScale` spec
+[source,yaml]
+----
+apiVersion: serving.knative.dev/v1
+kind: Service
+metadata:
+  name: example-service
+  namespace: default
+spec:
+  template:
+    metadata:
+      annotations:
+        autoscaling.knative.dev/maxScale: "10"
+...
+----
+
+include::modules/serverless-autoscaling-maxscale-kn.adoc[leveloffset=+3]
+
+[id="serverless-autoscaling-developer-concurrency"]
+== Concurrency
+
+Concurrency determines the number of simultaneous requests that can be processed by each replica of an application at any given time.
+
+include::modules/serverless-concurrency-limits.adoc[leveloffset=+2]
+include::modules/serverless-concurrency-limits-configure-soft.adoc[leveloffset=+2]
+include::modules/serverless-concurrency-limits-configure-hard.adoc[leveloffset=+2]
+include::modules/serverless-target-utilization.adoc[leveloffset=+2]
+
+[id="additional-resources_serverless-autoscaling-developer"]
+== Additional resources
+
+* Scale-to-zero can be enabled or disabled for the cluster by cluster administrators. For more information, see xref:../../serverless/admin_guide/serverless-admin-autoscaling.adoc#serverless-enable-scale-to-zero_serverless-admin-autoscaling[Enabling scale-to-zero].