Kubernetes 服务无法发现外部名称

Question

I'm deploying a nodejs application into a kubernetes cluster. This application needs access to an external database which is public available under db.external-service.com . For this purpose a service of the type ExternalName is created.

kind: Service
apiVersion: v1
metadata:
  name: postgres
spec:
  type: ExternalName
  externalName: db.external-service.com

In the deployment an environment variable which provides the database hostname for the application is set to the name of this service.

env:
  - name: DB_HOST
    value: postgres

The problem is that when the nodejs application try to connect to the database ends up with this error message.

Error: getaddrinfo ENOTFOUND postgres

Already tried to use the full hostname postgres.<my-namespace>.svc.cluster.local without success.

What cloud be wrong with this setup?

EDIT:

• It works if I use directly the plain ip address behind db.external-service.com in my pod configuration
• It dose not work if I use the hostname directly in my pod configuration
• I can ping the hostname with one of my pods: kubectl exec my-pod-xxx -- ping db.external-service.com has the right ip address

Answer 1

It turns out that the Kubernetes worker nodes are not on the allow list from the database. So the connection timed out.

Answer 2

• Seems like your Pod is not able to resolve DNS db.external-service.com to an IP Address.

• In Kubernetes, Pods use CoreDNS Pods to resolve Service Names to Service IP Addresses. https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/

• If CoreDNS Pods are not able to resolve the DNS to IP Address it is supposed to redirect the request to the Nameserver configured in the Host/VM/Node resolv.conf because dnsPolicy for CoreDNS Pods is Default. https://kubernetes.io/docs/concepts/services-networking/dns-pod-service/#pod-s-dns-policy

• So what is the dnsPolicy of your Pod?

• Are you able to resolve DNS db.external-service.com to an IP Address from the Host/VM/Node on which the CoreDNS Pod is running on?