Why can't I find service discovery in Kubernetes? - kubernetes

Question

I am creating a simple grpc example using Kubernetes in an on-premises environment.
When nodejs makes a request with pythonservice, pythonservice responds with helloworld and displays it on a web page.
However, pythonservice's clusterip is accessible, but not http://pythoservice:8000.
There may be a problem with coredns, so I checked various things and deleted kube-dns service of kube-system.
And if you check with pythonservice.default.svc.cluster.local with nslookup, you will see a different address from the clusterip of pythonservice.
Sorry I'm not good at English
This is the node.js code :
var setting = 'test';
var express = require('express');
var app = express();
const port = 80;
var PROTO_PATH = __dirname + '/helloworld.proto';
var grpc = require('grpc');
var protoLoader = require('#grpc/proto-loader');
var packageDefinition = protoLoader.loadSync(
PROTO_PATH,
{keepCase: true,
longs: String,
enums: String,
defaults: true,
oneofs: true
});
// http://pythonservice:8000
// 10.109.228.152:8000
// pythonservice.default.svc.cluster.local:8000
// 218.38.137.28
var hello_proto =
grpc.loadPackageDefinition(packageDefinition).helloworld;
function main(callback) {
var client = new hello_proto.Greeter("http://pythonservice:8000",
grpc.credentials.createInsecure());
var user;
if (process.argv.length >= 3) {
user = process.argv[2];
} else {
user = 'world';
}
client.sayHello({name: user}, function(err, response) {
console.log('Greeting:', response.message);
setting = response.message;
});
}
var server = app.listen(port, function () {});
app.get('/', function (req, res) {
main();
res.send(setting);
//res.send(ip2);
//main(function(result){
// res.send(result);
//})
});
This is the yaml file for pythonservice
apiVersion: apps/v1
kind: Deployment
metadata:
name: practice-dp2
spec:
selector:
matchLabels:
app: practice-dp2
replicas: 1
template:
metadata:
labels:
app: practice-dp2
spec:
hostname: appname
subdomain: default-subdomain
containers:
- name: practice-dp2
image: taeil777/greeter-server:v1
ports:
- containerPort: 8000
---
apiVersion: v1
kind: Service
metadata:
name: pythonservice
spec:
type: ClusterIP
selector:
app: practice-dp2
ports:
- port: 8000
targetPort: 8000
this is kubectl get all:
root#pusik-server0:/home/tinyos/Desktop/grpc/node# kubectl get all
NAME READY STATUS RESTARTS AGE
pod/practice-dp-55dd4b9d54-v4hhq 1/1 Running 1 68m
pod/practice-dp2-7d4886876-znjtl 1/1 Running 0 18h
NAME TYPE CLUSTER-IP EXTERNAL-IP
PORT(S) AGE
service/kubernetes ClusterIP 10.96.0.1 <none>
443/TCP 34d
service/nodeservice ClusterIP 10.100.165.53 <none>
80/TCP 68m
service/pythonservice ClusterIP 10.109.228.152 <none>
8000/TCP 18h
NAME READY UP-TO-DATE AVAILABLE AGE
deployment.apps/practice-dp 1/1 1 1 68m
deployment.apps/practice-dp2 1/1 1 1 18h
NAME DESIRED CURRENT READY
AGE
replicaset.apps/practice-dp-55dd4b9d54 1 1 1
68m
replicaset.apps/practice-dp2-7d4886876 1 1 1
18h
root#pusik-server0:/home/tinyos/Desktop/grpc/python# nslookup
pythonservice.default.svc.cluster.local
Server: 127.0.1.1
Address: 127.0.1.1#53
Name: pythonservice.default.svc.cluster.local
Address: 218.38.137.28

Answer 1

1. Answering the first question:
pythonservice's clusterip is accessible, but not http://pythoservice:8000.
Please refer to Connecting Applications with Services
The type of service/pythonservice is ClusterIP If you are interested with exposing the service outside the cluster please use service type NodePort or LoadBalancer. According to the attached screens, your application is accessible from within the cluster (ClusterIP serice).
2. Answering the second question:
The output
exec failed: container_linux.go:345: starting container process caused "exec: \"nslookup\": executable file not found in $PATH": unknown command terminated with exit code 126
means that inside your pod probably you don't have tools like nslookup so: please run some pod in the same namespace with installed tools and verify again:
kubectl run ubuntu --rm -it --image ubuntu --restart=Never --command -- bash -c 'apt-get update && apt-get -y install dnsutils && bash'
kubectl exec ubuntu2 -- nslookup pythonservice.default.svc.cluster.local
-- Update
Please verfify the state for all pods and svc especially in the kube-system namespace:
kubectl get nodes,pods,svc --all-namespaces -o wide
In order to start debugging please get more information about particular problem f.e. with coredns please use:
kubectl describe pod your coredns_pod -n kube-system
kubectl logs coredns_pod -n kube-system
Please refer to:
Debug Services
Debugging DNS Resolution
Hope this help.