Connecting to Kubernetes TCP and UDP services on the same IP - kubernetes

Question

I have 2 pods in a Kubernetes namespace. One uses TCP and the other uses UDP and both are exposed using ClusterIP services via external IP. Both services use the same external IP.
This way I let my users access both the services using the same IP.
I want to remove the use of spec.externalIPs but be able to allow my user to still use a single domain name/IP to access both the TCP and UDP services.
I do not want to use spec.externalIPs, so I believe clusterIP and NodePort services cannot be used. ​Load balancer service does not allow me to specify both TCP and UDP in the same service.
I have experimented with NGINX Ingress Controller. But even there the Load Balancer service needs to be created which cannot support both TCP and UDP in the same service.
Below is the cluster IP service exposing the apps currently using external IP:
apiVersion: v1
kind: Service
metadata:
labels:
app: tcp-udp-svc
name: tcp-udp-service
spec:
externalIPs:
- <public IP- IP2>
ports:
- name: tcp-exp
port: 33001
protocol: TCP
targetPort: 33001
- name: udp-exp
port: 33001
protocol: UDP
targetPort: 33001
selector:
app: tcp-udp-app
sessionAffinity: None
type: ClusterIP
The service shows up like below
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S)
tcp-udp-service ClusterIP <internal IP IP1> <public IP- IP2> 33001/TCP,33001/UDP
Using the above set up, both the TCP and UDP apps on port 33001 is accessible externally just fine using IP2.
As you can see I've used:
spec:
externalIPs:
- <public IP- IP2>
In the service to make it accessible externally.
However I do not want to use this set up, ie. I am looking for a set up without using the spec.externalIPs.
When using a load balancer service to expose the apps, I see that both TCP and UDP cannot be added in the same load balancer service. So I have to create one load balancer service for TCP and add another load balancer service for UDP like below
NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S)
tcp-service LoadBalancer <internal IP IP1> <public IP- IP2> 33001/TCP
udp-service LoadBalancer <internal IP IP3> <public IP- IP4> 33001/UDP
---
apiVersion: v1
kind: Service
metadata:
name: tcp-service
spec:
externalTrafficPolicy: Cluster
ports:
- name: tcp-svc
port: 33001
protocol: TCP
targetPort: 33001
selector:
app: tcp-udp-app
sessionAffinity: None
type: LoadBalancer
---
apiVersion: v1
kind: Service
metadata:
name: udp-service
spec:
externalTrafficPolicy: Cluster
ports:
- name: udp-svc
port: 33001
protocol: UDP
targetPort: 33001
selector:
app: tcp-udp-app
sessionAffinity: None
type: LoadBalancer
But the problem is that each of these services get individual IPs assigned (IP2 & IP4).
But I want to be able to access both the TCP & UDP apps using the same IP. When testing out with nginx ingress controller too, I am faced the same issue as above.
Is there any other possible way to achieve what I am looking for, ie. to expose both TCP and UDP services on the same IP, but without using the spec.externalIPs?

Answer 1

Unfortunately, you will not be able to achieve your desired result with Load Balancer. Service type in any way for UDP traffic, because according the following documentation UDP protocol is not supported by any of VPC load balancer types.
You could theoretically define a portable public IP address for LoadBalancer Service type, by using the loadBalancerIP annotation, but this portable public IP address has to be available in portable public subnet upfront and Cloud Provivers's LB needs to support UDP protocol. You can see this doc
Workaround for non-Prod setup:
You can use hostPort to expose TCP & UDP ports directly on worker nodes. Could be used together with some Ingress controllers that support TCP & UDP Services, like NGINX Ingress. For more see this documentation.