Can we create service to link two PODs from different Deployments > - kubernetes

Question

My application has to deployments with a POD.
Can I create a Service to distribute load across these 2 PODs, part of different deployments ?
If so, How ?

Answer 1

Yes it is possible to achieve. Good explanation how to do it can be found on Kubernete documentation. However, keep in mind that both deployments should provide the same functionality, as the output should have the same format.
A Kubernetes Service is an abstraction which defines a logical set of Pods running somewhere in your cluster, that all provide the same functionality. When created, each Service is assigned a unique IP address (also called clusterIP). This address is tied to the lifespan of the Service, and will not change while the Service is alive. Pods can be configured to talk to the Service, and know that communication to the Service will be automatically load-balanced out to some pod that is a member of the Service.
Based on example from Documentation.
1. nginx Deployment. Keep in mind that Deployment can have more than 1 label.
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx
spec:
selector:
matchLabels:
run: nginx
env: dev
replicas: 2
template:
metadata:
labels:
run: nginx
env: dev
spec:
containers:
- name: nginx
image: nginx
ports:
- containerPort: 80
2. nginx-second Deployment
apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-second
spec:
selector:
matchLabels:
run: nginx
env: prod
replicas: 2
template:
metadata:
labels:
run: nginx
env: prod
spec:
containers:
- name: nginx-second
image: nginx
ports:
- containerPort: 80
Now to pair Deployments with Services you have to use Selector based on Deployments labels. Below you can find 2 service YAMLs. nginx-service which pointing to both deployments and nginx-service-1 which points only to nginx-second deployment.
## Both Deployments
apiVersion: v1
kind: Service
metadata:
name: nginx-service
spec:
ports:
- port: 80
protocol: TCP
selector:
run: nginx
---
### To nginx-second deployment
apiVersion: v1
kind: Service
metadata:
name: nginx-service-1
spec:
ports:
- port: 80
protocol: TCP
selector:
env: prod
You can verify that service binds to deployment by checking the endpoints.
$ kubectl get pods -l run=nginx -o yaml | grep podIP
podIP: 10.32.0.9
podIP: 10.32.2.10
podIP: 10.32.0.10
podIP: 10.32.2.11
$ kk get ep nginx-service
NAME ENDPOINTS AGE
nginx-service 10.32.0.10:80,10.32.0.9:80,10.32.2.10:80 + 1 more... 3m33s
$ kk get ep nginx-service-1
NAME ENDPOINTS AGE
nginx-service-1 10.32.0.10:80,10.32.2.11:80 3m36s

Answer 2

Yes, you can do that.
Add a common label key pair to both the deployment pod spec and use that common label as selector in service definition
With the above defined service the requests would be load balanced across all the matching pods.