Kubernetes Cookbook: Building Cloud Native Applications

by Sebastien Goasguen

Kubernetes (commonly stylized as K8s[3]) is an open-source container-orchestration system for automating deployment, scaling and management of containerized applications.[4] It was originally designed by Google and is now maintained by the Cloud Native Computing Foundation. It aims to provide a "platform for automating deployment, scaling, and operations of application containers across clusters of hosts".[3] It works with a range of container tools, including Docker.

Keeping the mapping between the VIP and the pods up to date is the job of kube-proxy, a process that runs on every node on the cluster. This kube-proxy process queries the API server to learn about new services in the cluster and updates the node’s iptables rules (iptables) accordingly, to provide the necessary routing information.

you can automatically create a Service object using the kubectl expose command, like so:

Kubernetes uses the Service object to dynamically configure the iptables on all the nodes to be able to send the network traffic to the containers that make up the microservice.

If your service does not seem to be working properly, check the labels used in the selector and verify that a set of endpoints is being populated with kubectl get endpoints. If not, this most likely means that your selector is not finding any matching pods.

If the DNS cluster add-on is available and working properly, you can access the service via a fully qualified domain name (FQDN) in the form of $SERVICENAME.$NAMESPACE.svc.cluster.local.

Ingress rule

The kube-system namespace is reserved for administrators, whereas the kube-public namespace is meant to store public objects available to any users of the cluster.