Communication issue between frontend and backend pods using cluster IP, it works with Nodeport or Loadbalancer IP

Mani, Subhash 0

Communication issue between frontend and backend pods using cluster IP, it works with Node port or Load balancer IP.

I have a three-tier application which we have deployed as pods in AKS cluster. Front end is running using tomcat and backend is using jdk 11. Frontend pod is able to communicate with the backend pod only with public IP(either nodeport or LoadbalancerIP) it is not working with Cluster IP.
I do not want to expose the backend and the DB over the public IP but for some reason it is not working with cluster IP.

Mounika Reddy Anumandla 505 Reputation points Microsoft Vendor

2024-10-15T16:54:26.21+00:00
Hi Mani, Subhash,

Welcome to the Microsoft Q&A Platform! Thank you for asking your question here.

I can suggest you with some troubleshooting steps

Ensure that your backend service is correctly defined as a ClusterIP service. The frontend should access the backend using the service name rather than the pod IP. Whenever a front-end pod wants to communicate with backend pods, it has to simply communicate to a ClusterIP service name, which is a single endpoint service managing the communication to all backend pods.

Ensure that the tomcat frontend is using the correct IP addresses or DNS names to connect to the backend services.

Ensure that the tomcat frontend is using the correct API endpoints to connect to the backend services.

Additionally, I would suggest you go through Kubernetes documentation which might be helpful.
https://kubernetes.io/docs/tasks/access-application-cluster/connecting-frontend-backend/

If you have any further queries, do let us know.
Mounika Reddy Anumandla 505 Reputation points Microsoft Vendor

2024-10-16T15:20:06.6733333+00:00

Hi Mani, Subhash,

Hope you are doing well! Just checking to see if you had a chance to see my response to your question. If you have any further queries, do let us know.

If the answer is helpful, please click "Accept Answer" and "Upvote it."
Mounika Reddy Anumandla 505 Reputation points Microsoft Vendor

2024-10-17T09:20:29.8666667+00:00

Hi Mani, Subhash,

Just checking to see if you had a chance to see my response to your question. If you have any further queries, do let us know.

If the answer is helpful, please click "Accept Answer" and "Upvote it."
Mani, Subhash 0 Reputation points

2024-10-17T10:53:29.0533333+00:00

@Mounika Reddy Anumandla Thank you for looking into this.
I am new to Kubernetes so how I use to establish connections between pod, was using service type as nodeport.

So I use to give the IP or dns name of the node and the NodePort No as the connection string to call the API from frontend. which works however that is not what I want.
But prior to this I tried the service DNS in the format service-name.namespace.svc.cluster.local

which did not work, I was getting Network error.
I am not sure if we are missing anything in the tomcat configuration, like what is mentioned in the link that you have shared for nginx upstream configurations.
I will try with the service name as DNS in config map and update here.
If there is something I need to update in the tomcat server configuration do let me know, I will check that also.
Mounika Reddy Anumandla 505 Reputation points Microsoft Vendor

2024-10-17T13:44:12.8533333+00:00

Hi Mani, Subhash,

Thank you for reaching to us again!

I have investigated more on this context and thought this would help you.
As per my understanding, I think it would be better you go with headless services.
A Kubernetes headless service is a form of service that doesn’t allocate a cluster IP to represent a set of pods. Instead of load-balancing traffic across a group of pods, a headless service allows DNS queries for the service to go back to the individual IP addresses of all the pods associated with it. Headless service are useful in scenarios in which databases or other clustered applications want to discover and communicate with each other.

Unfortunately, if the pod is killed, in deployment a new pod will spin up but the pod name changes. So, we suggest you use stateful sets so that the pod name can't be changed if pod is killed. The new pod will spin up with the same name.

Headless services are usually used with StatefulSets, where every pod has a unique identity. This allows for direct conversation with particular pods. It’s also useful in scenarios requiring custom load balancing or direct communication with individual pods, such as in database clustering setups.
Additionally, I can provide you with some documents:
https://kubernetes.io/docs/concepts/services-networking/service/#headless-services
https://stackoverflow.com/questions/52707840/what-is-a-headless-service-what-does-it-do-accomplish-and-what-are-some-legiti

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Communication issue between frontend and backend pods using cluster IP, it works with Nodeport or Loadbalancer IP

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