How to make two Kubernetes Services talk to each other? - kubernetes

Question

Currently, I have working K8s API pods in a K8s service that connects to a K8s Redis service, with K8s pods of it's own. The problem is, I am using NodePort meaning BOTH are exposed to the public. I only want the API accessable to the public. The issue is that if I make the Redis service not public, the API can't see it. Is there a way to connect two Services without exposing one to the public?
This is my API service yaml:
apiVersion: v1
kind: Service
metadata:
name: app-api-svc
spec:
selector:
app: app-api
tier: api
ports:
- protocol: TCP
port: 5000
nodePort: 30400
type: NodePort
And this is my Redis service yaml:
apiVersion: v1
kind: Service
metadata:
name: app-api-redis-svc
spec:
selector:
app: app-api-redis
tier: celery_broker
ports:
- protocol: TCP
port: 6379
nodePort: 30537
type: NodePort

Answer 1

First, configure the Redis service as a ClusterIP service. It will be private, visible only for other services. This is could be done removing the line with the option type.
apiVersion: v1
kind: Service
metadata:
name: app-api-redis-svc
spec:
selector:
app: app-api-redis
tier: celery_broker
ports:
- protocol: TCP
port: 6379
targetPort: [the port exposed by the Redis pod]
Finally, when you configure the API to reach Redis, the address should be app-api-redis-svc:6379
And that's all. I have a lot of services communicating each other in this way. If this doesn't work for you, let me know in the comments.

Answer 2

I'm going to try to take the best from all answers and my own research and make a short guide that I hope you will find helpful:
1. Test connectivity
Connect to a different pod, eg ruby pod:
kubectl exec -it some-pod-name -- /bin/sh
Verify it can ping to the service in question:
ping redis
Can it connect to the port? (I found telnet did not work for this)
nc -zv redis 6379
2. Verify your service selectors are correct
If your service config looks like this:
kind: Service
apiVersion: v1
metadata:
name: redis
labels:
app: redis
role: master
tier: backend
spec:
ports:
- port: 6379
targetPort: 6379
selector:
app: redis
role: master
tier: backend
verify those selectors are also set on your pods?
get pods --selector=app=redis,role=master,tier=backend
Confirm that your service is tied to your pods by running:
$> describe service redis
Name: redis
Namespace: default
Labels: app=redis
role=master
tier=backend
Annotations: <none>
Selector: app=redis,role=master,tier=backend
Type: ClusterIP
IP: 10.47.250.121
Port: <unset> 6379/TCP
Endpoints: 10.44.0.16:6379
Session Affinity: None
Events: <none>
check the Endpoints: field and confirm it's not blank
More info can be found at:
https://kubernetes.io/docs/tasks/debug-application-cluster/debug-service/#my-service-is-missing-endpoints

Answer 3

I'm not sure about redis, but I have a similar application. I have a Java web application running as a pod that is exposed to the outside world through a nodePort. I have a mongodb container running as a pod.
In the webapp deployment specifications, I map it to the mongodb service through its name by passing the service name as parameter, I have pasted the specification below. You can modify accordingly.There should be a similar mapping parameter in Redis also where you would have to use the service name which is "mongoservice" in my case.
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: empappdepl
labels:
name: empapp
spec:
replicas: 1
template:
metadata:
labels:
name: empapp
spec:
containers:
- resources:
limits:
cpu: 0.2
image: registryip:5000/employee:1
imagePullPolicy: IfNotPresent
name: wsemp
ports:
- containerPort: 8080
name: wsemp
command: ["java","-Dspring.data.mongodb.uri=mongodb://mongoservice/microservices", "-Djava.security.egd=file:/dev/./urandom","-jar","/app.jar"]
imagePullSecrets:
- name: myregistrykey
---
apiVersion: v1
kind: Service
metadata:
labels:
name: empwhatever
name: empservice
spec:
ports:
- port: 8080
targetPort: 8080
protocol: TCP
name: http
nodePort: 30062
type: NodePort
selector:
name: empapp
---
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
name: mongodbdepl
labels:
name: mongodb
spec:
replicas: 1
template:
metadata:
labels:
name: mongodb
spec:
containers:
- resources:
limits:
cpu: 0.3
image: mongo
imagePullPolicy: IfNotPresent
name: mongodb
ports:
- containerPort: 27017
---
apiVersion: v1
kind: Service
metadata:
labels:
name: mongowhatever
name: mongoservice
spec:
ports:
- port: 27017
targetPort: 27017
protocol: TCP
selector:
name: mongodb
Note that the mongodb service doesnt need to be exposed as a NodePort.

Answer 4

Kubernetes enables inter service communication by allowing services communicate with other services using their service name.
In your scenario, redis service should be accessible from other services on
http://app-api-redis-svc.default:6379. Here default is the namespace under which your service is running.
This internally routes your requests to your redis pod running on the target container port
Checkout this link for different modes of service discovery options provided by kubernetes
Hope it helps