Basics
Services
Before we proceed, let’s check about Kubernetes service, A Kubernetes service is a logical abstraction for a deployed group of pods in a cluster (which all perform the same function). Since pods are ephemeral, a service enables a group of pods, which provide specific functions (web services, image processing, etc.) to be assigned a name and unique IP address (clusterIP). As long as the service is running that IP address, it will not change. Services also define policies for their access.
Types of Kubernetes services?
- ClusterIP. Exposes a service which is only accessible from within the cluster.
- NodePort. Exposes a service via a static port on each node’s IP.
- LoadBalancer. Exposes the service via the cloud provider’s load balancer.
- ExternalName. Maps a service to a predefined externalName field by returning a value for the CNAME record.
Container Network Interface
As we know, Every Pod in a cluster gets its own unique cluster-wide IP address. This means you do not need to explicitly create links between Pods and you almost never need to deal with mapping container ports to host ports. This creates a clean, backwards-compatible model where Pods can be treated much like VMs or physical hosts from the perspectives of port allocation, naming, service discovery, load balancing, application configuration, and migration.
Kubernetes imposes the following fundamental requirements on any networking implementation (barring any intentional network segmentation policies): pods can communicate with all other pods on any other node without NAT agents on a node (e.g. system daemons, kubelet) can communicate with all pods on that node.
Kubernetes networking addresses four concerns:
- Containers within a Pod use networking to communicate via loopback.
- Cluster networking provides communication between different Pods.
- The Service resource lets you expose an application running in Pods to be reachable from outside your cluster.
- You can also use Services to publish services only for consumption inside your cluster.
CNI Plugins:
Here are some familiar or most used CNI plugins,
- Flannel
- Calico
- Cilium
- WeaveNet
- Canal
Summary Matrix
