CODEWITHSUNDEEP
kuberneteskube-dns
Ryan
Ryan

Reputation: 1221

Service discovery on Kubernetes

I have kubeDNS set up on a bare metal kubernetes cluster. I thought that would allow me to access services as described here (http:// for those who don't want to follow the link), but when I run

curl https://monitoring-influxdb:8083

I get the error

curl: (6) Could not resolve host: monitoring-influxdb

This is true when I run curl on a service name in any namespace. Is this an error with my kubDNS setup or are there different steps I need to take in order to achieve this? I get the expected output when I run the test at the end of this article.

For reference:

kubeDNS controller yaml files

kubeDNS service yaml file

kubelet flags

output of kubectl get svc in default and kube-system namespaces

Upvotes: 1

Views: 3716

Answers (2)

Ryan
Ryan

Reputation: 1221

As @Michael Hausenblas pointed out in the comments, curl http://monitoring-influxdb:8086 needs to be run from within a pod. Doing that provided the expected results

Upvotes: 1

heckj
heckj

Reputation: 7357

The service discovery that you're trying to is documented at https://kubernetes.io/docs/concepts/services-networking/dns-pod-serv‌​ice, and is for communications within one pod talking to an existing service, not from nodes (or the master) to speak to Kubernetes services.

You will want to leverage the DNS for the service in form of <servicename>.<namespace> or <servicename>.<namespace>.svc.cluster.local. To see this in operation, kick up an interactive pod with busybox (or use an existing pod of your own) with something like:

  • kubectl run -i --tty alpine-interactive --image=alpine --restart=Never

and within that shell that is provided there, make an nslookup command. From your example, I'm guessing you're trying to access influxDB from https://github.com/kubernetes/heapster/tree/master/deploy/kube-config/influxdb, then it will be installed into the kube-system namespace, and the service name you'd use from another Pod internally to the cluster would be:

  • monitoring-influxdb.kube-system.svc.cluster.local

For example:

kubectl run -i --tty alpine --image=alpine --restart=Never
If you don't see a command prompt, try pressing enter.
/ # nslookup monitoring-influxdb.kube-system.svc.cluster.local
Server:    10.96.0.10
Address 1: 10.96.0.10 kube-dns.kube-system.svc.cluster.local

Name:      monitoring-influxdb.kube-system.svc.cluster.local
Address 1: 10.102.27.233 monitoring-influxdb.kube-system.svc.cluster.local

Upvotes: 6

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