Service Types

Take a look at the yaml that describes your web-service.

kubectl get svc web-service -o yaml

"svc" is a short-hand alias for "service", either will work in kubectl.

You should see a section that looks like this:

spec:
  clusterIP: 10.96.213.234
  ...
  type: ClusterIP

We didn't specify a service type! Why is this here? Well, it's because ClusterIP is the default service type.

The clusterIP is the IP address that the service is bound to on the internal Kubernetes network. Remember how we talked about how pods get their own internal, virtual IP address? Well, services can too! However, type: ClusterIP is just one type of service! There are several others, including:

• NodePort: Exposes the Service on each Node's IP at a static port.
• LoadBalancer: Creates an external load balancer in the current cloud environment (if supported, e.g. AWS, GCP, Azure) and assigns a fixed, external IP to the service.
• ExternalName: Maps the Service to the contents of the externalName field (for example, to the hostname api.foo.bar.example). The mapping configures your cluster's DNS server to return a CNAME record with that external hostname value. No proxying of any kind is set up.

The interesting thing about service types is that they typically build on top of each other. For example, a NodePort service is just a ClusterIP service with the added functionality of exposing the service on each node's IP at a static port (it still has an internal cluster IP).

A LoadBalancer service is just a NodePort service with the added functionality of creating an external load balancer in the current cloud environment (it still has an internal cluster IP and node port).

An ExternalName service is actually a bit different. All it does is a DNS-level redirect. You can use it to redirect traffic from one service to another.