Kubernetes services¶

This guide describes the Kubernetes Services that are active when running Knative Serving.

Before You Begin¶

This guide assumes that you have installed Knative Serving.

Verify that you have the proper components in your cluster. To view the services installed in your cluster, use the command:

$ kubectl get services -n knative-serving

This returns an output similar to the following:

NAME                TYPE        CLUSTER-IP       EXTERNAL-IP   PORT(S)                  AGE
activator-service   ClusterIP   10.96.61.11      <none>        80/TCP,81/TCP,9090/TCP   1h
autoscaler          ClusterIP   10.104.217.223   <none>        8080/TCP,9090/TCP        1h
controller          ClusterIP   10.101.39.220    <none>        9090/TCP                 1h
webhook             ClusterIP   10.107.144.50    <none>        443/TCP                  1h

To view the deployments in your cluster, use the following command:

$ kubectl get deployments -n knative-serving

This returns an output similar to the following:

NAME                         DESIRED   CURRENT   UP-TO-DATE   AVAILABLE   AGE
activator                    1         1         1            1           1h
autoscaler                   1         1         1            1           1h
controller                   1         1         1            1           1h
net-certmanager-controller   1         1         1            1           1h
net-istio-controller         1         1         1            1           1h
webhook                      1         1         1            1           1h

These services and deployments are installed by the serving.yaml file during install. The next section describes their function.

Components¶

Service: activator¶

The activator is responsible for receiving & buffering requests for inactive revisions and reporting metrics to the autoscaler. It also retries requests to a revision after the autoscaler scales the revision based on the reported metrics.

Service: autoscaler¶

The autoscaler receives request metrics and adjusts the number of pods required to handle the load of traffic.

Service: controller¶

The controller service reconciles all the public Knative objects and autoscaling CRDs. When a user applies a Knative service to the Kubernetes API, this creates the configuration and route. It will convert the configuration into revisions and the revisions into deployments and Knative Pod Autoscalers (KPAs).

Service: webhook¶

The webhook intercepts all Kubernetes API calls as well as all CRD insertions and updates. It sets default values, rejects inconsistent and invalid objects, and validates and mutates Kubernetes API calls.

Deployment: net-certmanager-controller¶

The certmanager reconciles cluster ingresses into cert manager objects.

Deployment: net-istio-controller¶

The net-istio-controller deployment reconciles a cluster's ingress into an Istio virtual service.

What's Next¶

For a deeper look at the services and deployments involved in Knative Serving, see the specs repository.
For a high-level analysis of Knative Serving, see the Knative Serving overview.
For hands-on tutorials, see the Knative Serving code samples.