Kubernetes External Access Of A Single Pod

Question

I am running a kubernetes cluster in AWS. I have 2 nodes. I have one pod that should be accessible externally. The problem is, that pod can be on either node.

The solution according to the docs:

1. Expose the deployment as a NodePort service.
2. get pods to find the name of the node running the pod.
3. get nodes to find the IP address of the named node.
4. Open the NodePort port through EC2 Security Group.

The problem here is that this pod could be restarted/switch nodes, I think? At that point the application will be unavailable by the previous node IP address.

How can I make sure an application is always available, even if this specific pod switches nodes during a restart/etc?

Note: I definitely only want one of this specific pod. I do not want replicas.

Answer 1

The NodePort will resolve correctly, no matter the node where the pods is (even if it gets rescheduled on a different node).

Any <Node IP>:<NodePort> will resolve to a Service type NodePort, no matter what node the pods are running.

Every node will forward traffic to that port to the Service.

You need to be on the same network (or create a SSH tunnel) or open that port in one of your nodes to the world.

Answer 2

I am going to put some concreteness to @Tensibai's recommendation in the comments. I began looking into Ingress and Ingress controllers, but my knowledge/implementation was wrong. I successfully connected via an Ingress, but I felt, at least my implementation, it still depended on the node the ingress was running on.

So, I began looking at ELB on AWS. I couldn't find any good tutorials on implementing this specific for AWS. The official docs actually helped more than I was aware. It ended up being embarrassingly easy. I made a single change to my service yaml:

type: NodePort

to

type: LoadBalancer

and applied it via kubectl apply -f my-file.yaml

You can then find the external IP:

$ kubectl get svc
NAME             TYPE           CLUSTER-IP      EXTERNAL-IP        PORT(S)
my-service       LoadBalancer   100.99.98.97    12.34.56.78        444:31415/TCP

One part I was not expecting is that the first port 444 is used, rather than the NodePort (31415 in my case).

To access my app I would use: 12.34.56.78:444

The second part I was not expecting is that the external IP, in my case on AWS, was an ELB. It was created automatically in AWS. I am not sure if kubernetes does this, or kops? Maybe someone can clarify in the comments.

Answer 3

you can use the feature of port-forward using kubectl,

Examples:
  # Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in the pod
  kubectl port-forward pod/mypod 5000 6000

  # Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in a pod selected by the
deployment
  kubectl port-forward deployment/mydeployment 5000 6000

  # Listen on port 8888 locally, forwarding to 5000 in the pod
  kubectl port-forward pod/mypod 8888:5000

  # Listen on a random port locally, forwarding to 5000 in the pod
  kubectl port-forward pod/mypod :5000 

But if you want to expose your pod, so that other pods can communicate to it, use services. K8s service