Concepts

Deployment

The configuration of a standard Cilium Kubernetes deployment consists of several Kubernetes resources:

  • A DaemonSet resource: describes the Cilium pod that is deployed to each Kubernetes node. This pod runs the cilium-agent and associated daemons. The configuration of this DaemonSet includes the image tag indicating the exact version of the Cilium docker container (e.g., v1.0.0) and command-line options passed to the cilium-agent.
  • A ConfigMap resource: describes common configuration values that are passed to the cilium-agent, such as the kvstore endpoint and credentials, enabling/disabling debug mode, etc.
  • ServiceAccount, ClusterRole, and ClusterRoleBindings resources: the identity and permissions used by cilium-agent to access the Kubernetes API server when Kubernetes RBAC is enabled.
  • A Secret resource: describes the credentials use access the etcd kvstore, if required.

Networking For Existing Pods

In case pods were already running before the Cilium DaemonSet was deployed, these pods will still be connected using the previous networking plugin according to the CNI configuration. A typical example for this is the kube-dns service which runs in the kube-system namespace by default.

A simple way to change networking for such existing pods is to rely on the fact that Kubernetes automatically restarts pods in a Deployment if they are deleted, so we can simply delete the original kube-dns pod and the replacement pod started immediately after will have networking managed by Cilium. In a production deployment, this step could be performed as a rolling update of kube-dns pods to avoid downtime of the DNS service.

$ kubectl --namespace kube-system delete pods -l k8s-app=kube-dns
pod "kube-dns-268032401-t57r2" deleted

Running kubectl get pods will show you that Kubernetes started a new set of kube-dns pods while at the same time terminating the old pods:

$ kubectl --namespace kube-system get pods
NAME                          READY     STATUS        RESTARTS   AGE
cilium-5074s                  1/1       Running       0          58m
kube-addon-manager-minikube   1/1       Running       0          59m
kube-dns-268032401-j0vml      3/3       Running       0          9s
kube-dns-268032401-t57r2      3/3       Terminating   0          57m

Default Ingress Allow from Local Host

Kubernetes has functionality to indicate to users the current health of their applications via Liveness Probes and Readiness Probes. In order for kubelet to run these health checks for each pod, by default, Cilium will always allow all ingress traffic from the local host to each pod.