Services

Cluster IP

kind: Service
apiVersion: v1
metadata:
  name: my-awesome-service
spec:
  type: ClusterIP
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 32768
    targetPort: 80

NodePort

kind: Service
apiVersion: v1
metadata:
  name: my-awesome-service
spec:
  type: NodePort
  selector:
    app: nginx
  ports:
  - protocol: TCP
    port: 32768  # Service Port
    targetPort: 80 # Pod Port
    nodePort: 30080 # Node Port

LoadBalancer

apiVersion: v1
kind: Service
metadata:
  name: nginx-loadbalancer
spec:
  type: LoadBalancer
  ports:
  - port: 80
    targetPort: 80
  selector:
    app: nginx

# Study Things
# Set the annotation to route load balancer traffic local to the node:

kubectl annotate service kubeserve2 externalTrafficPolicy=Local

# https://kubernetes.io/docs/tutorials/services/source-ip/#source-ip-for-services-with-type-clusterip

Headless

Test

Excert from Kubenertes in Action by Marco Luksa

Each connection to the service is forwarded to one randomly selected backing pod. But what if the client needs to connect to all of those pods? What if the backing pods themselves need to each connect to all the other backing pods. Connecting through the service clearly isn’t the way to do this. What is?
For a client to connect to all pods, it needs to figure out the the IP of each individual pod. One option is to have the client call the Kubernetes API server and get the list of pods and their IP addresses through an API call, but because you should always strive to keep your apps Kubernetes-agnostic, using the API server isn’t ideal
Luckily, Kubernetes allows clients to discover pod IPs through DNS lookups. Usually, when you perform a DNS lookup for a service, the DNS server returns a single IP — the service’s cluster IP. But if you tell Kubernetes you don’t need a cluster IP for your service (you do this by setting the clusterIP field to None in the service specification ), the DNS server will return the pod IPs instead of the single service IP. Instead of returning a single DNS A record, the DNS server will return multiple A records for the service, each pointing to the IP of an individual pod backing the service at that moment. Clients can therefore do a simple DNS A record lookup and get the IPs of all the pods that are part of the service. The client can then use that information to connect to one, many, or all of them.
Setting the clusterIP field in a service spec to None makes the service headless, as Kubernetes won’t assign it a cluster IP through which clients could connect to the pods backing it.

apiVersion: v1
kind: Service
metadata:
  name: kube-headless
spec:
  clusterIP: None
  ports:
  - port: 80
    targetPort: 8080
  selector:
    app: kubserve2

Troubleshooting

# Look at the iptables rules for your services:
sudo iptables-save | grep KUBE | grep nginx