Service not available in Kubernetes - kubernetes

Question

I have a minikube cluster running locally (v0.17.1), with two deployments: one is a Redis instance and one is a custom app that is trying to connect to the Redis instance. My configuration is more or less copy/pasted from the official docs and the Kubernetes guestbook example.
Service definition and deployment:
apiVersion: v1
kind: Service
metadata:
name: poller-redis
labels:
app: poller-redis
tier: backend
role: database
target: poller
spec:
selector:
app: poller
tier: backend
role: service
ports:
- port: 6379
targetPort: 6379
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: poller-redis
spec:
replicas: 1
template:
metadata:
labels:
app: poller-redis
tier: backend
role: database
target: poller
spec:
containers:
- name: poller-redis
image: gcr.io/jmen-1266/jmen-redis:a67b5f4bfd8ea8441ed66a8fcb6596f276017a1c
ports:
- containerPort: 6379
env:
- name: GET_HOSTS_FROM
value: dns
imagePullSecrets:
- name: gcr-json-key
App deployment:
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: poller
spec:
replicas: 1
template:
metadata:
labels:
app: poller
tier: backend
role: service
spec:
containers:
- name: poller
image: gcr.io/jmen-1266/poller:a96a452292e894e46339309cc024cac67647cc25
imagePullPolicy: Always
imagePullSecrets:
- name: gcr-json-key
Relevant (I hope) Kubernetes info:
$ kubectl get services
NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
kubernetes 10.0.0.1 <none> 443/TCP 24d
poller-redis 10.0.0.137 <none> 6379/TCP 20d
$ kubectl get deployments
NAME DESIRED CURRENT UP-TO-DATE AVAILABLE AGE
poller 1 1 1 1 12d
poller-redis 1 1 1 1 4d
$ kubectl get endpoints
NAME ENDPOINTS AGE
kubernetes 10.0.2.15:8443 24d
poller-redis 172.17.0.7:6379 20d
Inside the poller pod (custom app), I get environment variables created for Redis:
# env | grep REDIS
POLLER_REDIS_SERVICE_HOST=10.0.0.137
POLLER_REDIS_SERVICE_PORT=6379
POLLER_REDIS_PORT=tcp://10.0.0.137:6379
POLLER_REDIS_PORT_6379_TCP_ADDR=10.0.0.137
POLLER_REDIS_PORT_6379_TCP_PORT=6379
POLLER_REDIS_PORT_6379_TCP_PROTO=tcp
POLLER_REDIS_PORT_6379_TCP=tcp://10.0.0.137:6379
However, if I try to connect to that port, I cannot. Doing something like:
nc -vz poller-redis 6379
fails.
What I have noticed is that I cannot access the Redis service via its ClusterIP but I can via the IP of the pod running Redis.
Any ideas, please?

Answer 1

Figured this out in the end, it looks like I misunderstood how the service selectors work in Kubernetes.
I have posted that my service definition is:
apiVersion: v1
kind: Service
metadata:
name: poller-redis
labels:
app: poller-redis
tier: backend
role: database
target: poller
spec:
selector:
app: poller
tier: backend
role: service
ports:
- port: 6379
targetPort: 6379
The problem is that metadata.labels and spec.selector are different, when they should actually be the same. I still do not exactly understand why this is the case judging by the Kubernetes documentation, but there you have it. Now my service definition looks like:
apiVersion: v1
kind: Service
metadata:
name: poller-redis
labels:
app: poller-redis
tier: backend
role: database
target: poller
spec:
selector:
app: poller-redis
tier: backend
role: database
target: poller
ports:
- port: 6379
targetPort: 6379
I also now use straight up DNS lookup (i.e. ping poller-redis) rather than trying to connect to localhost:6379 from my target pods.

Answer 2

It could be related to kube-dns possibly not running.
From inside the poller pod can you verify that poller-redis resolves?
Does the following work from inside the container?
nc -v 10.0.0.137

Answer 3

One kube-dns service running in kube-system is enough. Did you run nc -vz poller-redis 6379 in pods which have same namespace as redis service?
poller-redis is simplified dns name of resdis service in same namespace. It will do not work in different namespace.
Since kube-dns is unavailable on nodes. So if you want to run nc or redisclient in nodes, please use clusterIP of redis service to replace dns name.