Kubernetes, access IP outside the cluster - networking

Question

I have a corporate network(10.22..) which hosts a Kubernetes cluster(10.225.0.1). How can I access some VM in the same network but outside the cluster from within the pod in the cluster?
For example, I have a VM with IP 10.22.0.1:30000, which I need to access from a Pod in Kubernetes cluster. I tried to create a Service like this
apiVersion: v1
kind: Service
metadata:
name: vm-ip
spec:
selector:
app: vm-ip
ports:
- name: vm
protocol: TCP
port: 30000
targetPort: 30000
externalIPs:
- 10.22.0.1
But when I do "curl http://vm-ip:30000" from a Pod(kubectl exec -it), it returns "connection refused" error. But it works with "google.com". What are the ways of accessing the external IPs?

Answer 1

You can create an endpoint for that.
Let's go through an example:
In this example, I have a http server on my network with IP 10.128.15.209 and I want it to be accessible from my pods inside my Kubernetes Cluster.
First thing is to create an endpoint. This is going to let me create a service pointing to this endpoint that will redirect the traffic to my external http server.
My endpoint manifest is looking like this:
apiVersion: v1
kind: Endpoints
metadata:
name: http-server
subsets:
- addresses:
- ip: 10.128.15.209
ports:
- port: 80
$ kubectl apply -f http-server-endpoint.yaml
endpoints/http-server configured
Let's create our service:
apiVersion: v1
kind: Service
metadata:
name: http-server
spec:
ports:
- port: 80
targetPort: 80
$ kubectl apply -f http-server-service.yaml
service/http-server created
Checking if our service exists and save it's clusterIP for letter usage:
user#minikube-server:~$$ kubectl get service
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
http-server ClusterIP 10.96.228.220 <none> 80/TCP 30m
kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 10d
Now it's time to verify if we can access our service from a pod:
$ kubectl run ubuntu -it --rm=true --restart=Never --image=ubuntu bash
This command will create and open a bash session inside a ubuntu pod.
In my case I'll install curl to be able to check if I can access my http server. You may need install mysql:
root#ubuntu:/# apt update; apt install -y curl
Checking connectivity with my service using clusterIP:
root#ubuntu:/# curl 10.128.15.209:80
Hello World!
And finally using the service name (DNS):
root#ubuntu:/# curl http-server
Hello World!
So, in your specific case you have to create this:
apiVersion: v1
kind: Endpoints
metadata:
name: vm-server
subsets:
- addresses:
- ip: 10.22.0.1
ports:
- port: 30000
---
apiVersion: v1
kind: Service
metadata:
name: vm-server
spec:
ports:
- port: 30000
targetPort: 30000