Services and port forwarding
============================

Exposing a resource (e.g. pod, replicaset, or deployment) using `kubectl` creates a service:

```console
$ kubectl run pod-hello --image=pbitty/hello-from --port=80
pod/pod-hello created

$ kubectl expose pod pod-hello --type=NodePort
service/pod-hello exposed
```

We can now access the `pod-hello` service from the host machine:

```console
$ minikube service pod-hello --url
http://192.168.49.2:31500

$ curl $(minikube service pod-hello --url); echo
Hello from pod-hello (10.244.0.7)
```

Note that the IP address returned by `curl` (`10.xx.xx.xx`) is for the minikube cluster's internal network, while the IP address returned by the first command (`192.168.49.xx`) is for the bridge network used by Minikube. To expose the service to other machines, we need port forwarding:

```console
$ kubectl port-forward --address 0.0.0.0 svc/pod-hello 8000:80
Forwarding from 0.0.0.0:8000 -> 80
```

![](/_static/images/svc-port-forward.png)

We can, of course, relegate our port-forwarding tasks to the background:

```console
$ kubectl port-forward --address 0.0.0.0 svc/pod-hello 8000:80 &>/dev/null &
[1] 698879
$ kubectl port-forward --address 0.0.0.0 svc/pod-hello 8080:80 &>/dev/null &
[2] 699035
$ kubectl port-forward --address 0.0.0.0 svc/pod-hello 8888:80 &>/dev/null &
[3] 699192
$ jobs
[1]   Running                 kubectl port-forward --address 0.0.0.0 svc/pod-hello 8000:80 &> /dev/null &
[2]-  Running                 kubectl port-forward --address 0.0.0.0 svc/pod-hello 8080:80 &> /dev/null &
[3]+  Running                 kubectl port-forward --address 0.0.0.0 svc/pod-hello 8888:80 &> /dev/null &
$ kill %1
[1]   Terminated              kubectl port-forward --address 0.0.0.0 svc/pod-hello 8000:80 &> /dev/null
$ kill %2
[2]-  Terminated              kubectl port-forward --address 0.0.0.0 svc/pod-hello 8080:80 &> /dev/null
$ kill %3
[3]+  Terminated              kubectl port-forward --address 0.0.0.0 svc/pod-hello 8888:80 &> /dev/null
$ jobs
```

Note how we were able to expose multiple ports, all pointing to the same service.

Clean up by deleting the created pod and service:

```console
$ kubectl delete pod/pod-hello service/pod-hello
pod "pod-hello" deleted
service "pod-hello" deleted
```

## YAML specification

:::{code-block} yaml
:caption: pod-hello-svc.yaml

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod-hello
  name: pod-hello
spec:
  containers:
    - image: pbitty/hello-from
      name: pod-hello
      ports:
        - containerPort: 80
  dnsPolicy: ClusterFirst
  restartPolicy: Always
---
apiVersion: v1
kind: Service
metadata:
  name: pod-hello
spec:
  selector:
    run: pod-hello
  type: NodePort
  ports:
  - name: http
    protocol: TCP
    port: 8000
    targetPort: 80
    nodePort: 31080
:::

```{kroki}
:type: plantuml
:caption: Right click > "Open image in new tab" to view full-size.

@startyaml
#highlight metadata/labels/run

apiVersion: v1
kind: Pod
metadata:
  creationTimestamp: null
  labels:
    run: pod-hello
  name: pod-hello
spec:
  containers:
    - image: pbitty/hello-from
      name: pod-hello
      ports:
        - containerPort: 80
  dnsPolicy: ClusterFirst
  restartPolicy: Always
@endyaml
```

```{kroki}
:type: plantuml

@startyaml
#highlight spec/selector/run

apiVersion: v1
kind: Service
metadata:
  name: pod-hello
spec:
  selector:
    run: pod-hello
  type: NodePort
  ports:
  - name: http
    protocol: TCP
    port: 8000
    targetPort: 80
    nodePort: 31080
@endyaml
```

Note that the selector for the service matches the label for the pod.

```console
$ kubectl create -f pod-hello-svc.yaml
pod/pod-hello created
service/pod-hello created
$ curl `minikube service pod-hello --url`; echo
Hello from pod-hello (10.244.0.8)
$ kubectl get svc,pod
NAME                 TYPE        CLUSTER-IP      EXTERNAL-IP   PORT(S)          AGE
service/kubernetes   ClusterIP   10.96.0.1       <none>        443/TCP          5h20m
service/pod-hello    NodePort    10.98.186.154   <none>        8000:31080/TCP   91s

NAME            READY   STATUS    RESTARTS   AGE
pod/pod-hello   1/1     Running   0          91s
$ kubectl port-forward --address 0.0.0.0 svc/pod-hello 8000:8000 &>/dev/null &
[1] 705964
```

The service can now be accessed externally as before.