The Knative project combines elements of existing CNCF projects such as Kubernetes, Istio, Prometheus, and Grafana and eventing engines such as Kafka and Google Pub/Sub. Knative runs as a Kubernetes operator using Kubernetes Custom Resource Definitions (CRDs), which help operators administer Knative using the kubectl command line. Knative provides its API for developers, which the kn command-line utility can use. The users are provided access through Istio, which, with its traffic managementfeatures, is a crucial component of Knative. The following diagram describes
this graphically:
Figure 7.2 – Knative architecture
Knative consists of two main modules—serving and eventing. While the serving module helps us maintain stateless applications using HTTP/S endpoints, the eventing module integrates with eventing engines such as Kafka and Google Pub/Sub. As we’ve discussed mostly HTTP/S traffic, we will scope our discussion to Knative serving for this book.
Knative maintains serving pods, which help route traffic within workload pods and act as proxies using the Istio Ingress Gateway component. It provides a virtual endpoint for your service and listens to it. When it discovers a hit on the endpoint, it creates the required Kubernetes components to serve that traffic. Therefore, Knative has the functionality to scale from zero workload pods as it will spin up a pod when it receives traffic for it. The followingdiagram shows how:
Figure 7.3 – Knative serving architecture
Knative endpoints are made up of three basic parts—<app-name>, <namespace>, and <custom-domain>. While name and namespace are similar to Kubernetes Services, custom-domain is defined by us. It can be a legitimate domain for your organization or a MagicDNS solution, such as sslip.io, which we will use in our hands-on exercises. If you are using your organization domain, you must create your DNS configuration to resolve the domain to the Istio Ingress Gateway IP addresses.
Now, let’s go ahead and install Knative.
For the exercises, we will use GKE. Since GKE is a highly robust Kubernetes cluster, it is a great choice for integrating with Knative. As mentioned previously, Google Cloud provides a free trial of $300 for 90 days. You can sign up at https://cloud.google.com/free if you’ve not done so already.
