Kubernetes Services insights Pt2

2 minutes read
kubernetes • docker

In the first part we discussed pods communication through Kubernetes services, all of this internally in the cluster, but what if we need to expose the service to the internet?

Exposing services to the internet

Node Port

The service type NodePort creates a unique port in every node of the cluster and forwards the requests to the pods that are part of that service.

apiVersion: v1
kind: Service
metadata:
  name: example-nodeport
spec:
  type: NodePort             ❶
  ports:
  - port: 80                 ❷
    targetPort: 80           ❸
    nodePort: 30021          ❹
  selector:
    app: example

❶ Set the service type to NodePort.

❷ Port of the service’s internal cluster IP.

❸ Target port of the backing pods.

❹ The service will be accessible through port 30021 of each of your cluster node (no requiered, if missing Kubernetes will choose a random port)

$ kubectl get service example-nodeport
NAME               CLUSTER-IP       EXTERNAL-IP   PORT(S)        AGE
example-nodeport   10.110.254.212   <nodes>       80:30021/TCP   14m

Now you can access the service via the Node public IP address. Let’s assume that the public IP address of one of our nodes is 35.203.63.213

curl http://35.203.63.213:30021
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
</head>
...

LoadBalancer

The LoadBalancer service type is an extension of the NodePort type service. Is only supported in Kubernetes clusters running in Cloud Service providers like AWS and GCP.

If the Kubernetes cluster does not support the LoadBalancer service type then a NodePort service will be created instead.

elb

Ingress Resource

The Ingress resource is a controller that runs in the cluster. It operates at the layer 7 (application) level offering different options to route traffic to one or more services using a single endpoint.

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: example
spec:
  rules:
  - host: service.libert.xyz
    http:
      paths:
      - path: /
        backend:
          serviceName: example-nodeport
          servicePort: 80

Now you can access the ingress using the hostname.

$ curl http://service.libert.xyz
<!DOCTYPE html>
<html>
<head>
<title>Welcome to nginx!</title>
</head>
...

The workflow starts with a DNS lookup of service.libert.xyz to getthe IP of the Ingress controller.

The client then sent an HTTP request to the Ingress controller and specified service.libert.xyz in the Host header.

From that header, the Ingress controller determines which service the client is trying to access, looked up the pod IPs through the Endpoints object associated with the service, and forwards the client’s request to one of the pods.

In the following example, we can see how we can route the traffic to different services using a single endpoint.

...
  - host: service.libert.xyz
    http:
      paths:
      - path: /health                ❶
        backend:                     ❶
          serviceName: foo           ❶
          servicePort: 80            ❶
      - path: /bar                   ❷
        backend:                     ❷
          serviceName: bar           ❷
          servicePort: 80            ❷

*** References - Kubernetes in Action