What host does Kubernetes assign to my deployment? - kubernetes

Question

I have two Kubernetes deployments: composite-app (1 pod) and product-app (2 pods), both listening in port 8080. The first one needs to call the second one sometimes.
However, the first deployment can't find the second one. When it tries to call it using the product.app host it fails:
Exception: I/O error on GET request for "http://product-app:8080/product/123": product-app;
nested exception is UnknownHostException
Am I using the right host? So far I've tried (to no avail):
product
product-app.default.pod.cluster.local
product-app
Here's my YAML:
apiVersion: v1
kind: Service
metadata:
name: composite-service
spec:
type: NodePort
selector:
app: composite-app
ports:
- targetPort: 8080
port: 8080
nodePort: 30091
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: composite-deploy
spec:
replicas: 1
selector:
matchLabels:
app: composite-app
template:
metadata:
labels:
app: composite-app
spec:
containers:
- name: composite-container
image: 192.168.49.2:2376/composite-ms:latest
imagePullPolicy: Never
ports:
- containerPort: 8080
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: product-deploy
spec:
replicas: 2
selector:
matchLabels:
app: product-app
template:
metadata:
labels:
app: product-app
spec:
containers:
- name: product-container
image: 192.168.49.2:2376/product-ms:latest
imagePullPolicy: Never
ports:
- containerPort: 8080

Answer 1

You need to define a Service object for the product-deploy Deployment as well for the other pod to be able to connect to it. The Service can be of type ClusterIP if it is not needed to be exposed to the external world.
apiVersion: v1
kind: Service
metadata:
name: product-service
spec:
type: ClusterIP
selector:
app: product-app
ports:
- targetPort: 8080
port: 8080
---
apiVersion: apps/v1
kind: Deployment
metadata:
name: product-deploy
spec:
replicas: 2
selector:
matchLabels:
app: product-app
template:
metadata:
labels:
app: product-app
spec:
containers:
- name: product-container
image: 192.168.49.2:2376/product-ms:latest
imagePullPolicy: Never
ports:
- containerPort: 8080
You can connect to the other pod using the pod's IP without the service. However, that is not recommended since the pod's IP can be changed across pod updates.
You can then connect to the product-app pod from the composite-app using product-service.