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
The service discovery that you're trying to is documented at https://kubernetes.io/docs/concepts/services-networking/dns-pod-service, 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
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
Related
I have gone through the doc mentioned here gitlink as well as doclink
But my job would be a whole lot easier if I could get the dns of a resource type by using any kubernetes command.
Also tried this commands-link
For example, i would like to get the dns name of a service db-service running in dev namespace inside svc.cluster.local
db-service.dev.svc.cluster.local
Any pointers ?
If you need to, you can query that in a pod:
How do I run a container from the command line in Kubernetes (like docker run)?
Retrieve the full name of a service in Kubernetes
using a pod which has some DNS utils
kubectl run tmp-shell --rm -i --tty --image tutum/dnsutils -- /bin/bash
you can then run
root#tmp-shell:/# nslookup db-service
Server: 10.2.32.10
Address: 10.2.32.10#53
Name: db-service.dev.svc.cluster.local
for a one-liner, see: https://serverfault.com/questions/929211/kubernetes-pod-dns-resolution
Try command
kubectl get svc
First column is internal DNS name.
If the type is LoadBalancer then EXTERNAL-IP column will display the external DNS name.
I would like to execute a command on a node from the master. For e.g let's say I have worker node: kubenode01
Now a pod (pod-test) is running on this node. Using "kubectl get pods --output=wide" on the master shows that the pod is running on this node.
Trying to execute a command on that pod from the master results into an error e.g:
kubectl exec -ti pod-test -- cat /etc/resolv.conf
The result is:
Error from server: error dialing backend: dial tcp 10.0.22.131:10250: i/o timeout
Any idea?
Thanks in advance
You can execute kubectl commands from anywhere as long as your kubeconfig is configured to point to the right cluster URL (kube-apiserver), with the right credentials and the firewall allows connecting to the kube-apiserver port.
In your case, I'd check if your 10.0.22.131:10250 is the real IP:PORT for your kube-apiserver and that you can access it.
Note that kubectl exec -ti pod-test -- cat /etc/resolv.conf runs on the Pod and not on the Node. If you'd like to run on the Node just simply use SSH.
Update:
There are two other alternatives here:
You can create a pod (or debug pod) with a nodeSelector that specifically makes that pod run on the specific node.
If you are trying to debug something on a pod already running on a specific node, you can also try creating a debug ephemeral container.
On newer versions of Kubernetes you can use a debug pod to run something on a specific node
✌️
I create a pod to test my service in kubernetes. But i didn't get anythings. Here is my command
kubectl run --generator=run-pod/v1 nginx-resolver --image=nginx
kubectl expose pod nginx-resolver --name=nginx-resolver-service --port=80 --target-port=80 --type=ClusterIP
kubectl run --generator=run-pod/v1 test-nslookup --image=busybox:1.28 --rm -it -- nslookup nginx-resolver-service
Please help me explain why. Thanks
Run the following command and get things what you are thinking wrong about this cmd.
$ kubectl run --help
Create and run a particular image, possibly replicated.
Creates a deployment or job to manage the created container(s).
Examples:
# Start a single instance of nginx.
kubectl run nginx --image=nginx
# Start a single instance of hazelcast and let the container expose port 5701 .
kubectl run hazelcast --image=hazelcast --port=5701
...
So, kubectl run cmd creates a deployment or a job
If it is a deployment, it creates (a) first, a replicaset, (b) then Pod(s).
If it is a job, it creates a Pod.
But you are trying to expose a Pod which name is not the correct one. You can see the name of the Pod that is/are created by the cmd kubectl run.
$ kubectl get pods --namespace=<namespace> | grep "nginx-resolver"
$ kubectl get pods --namespace=<namespace> | grep "test-nslookup"
Then use those names to expose Pod.
You can optionally expose your Deployment. To do so, see the help of $ kubectl expose deployment --help. Run:
$ kubectl expose deployment --help
Expose a resource as a new Kubernetes service.
Looks up a deployment, service, replica set, replication controller or pod by name and uses the selector for that
resource as the selector for a new service on the specified port. A deployment or replica set will be exposed as a
service only if its selector is convertible to a selector that service supports, i.e. when the selector contains only
the matchLabels component. Note that if no port is specified via --port and the exposed resource has multiple ports, all
will be re-used by the new service. Also if no labels are specified, the new service will re-use the labels from the
resource it exposes.
Possible resources include (case insensitive):
pod (po), service (svc), replicationcontroller (rc), deployment (deploy), replicaset (rs)
Examples:
...
# Create a service for an nginx deployment, which serves on port 80 and connects to the containers on port 8000.
kubectl expose deployment nginx --port=80 --target-port=8000
...
If you want to see the log interactively, you need to set the --restart option of your test-nslookup pod to Never or OnFailure. Otherwise, kubernetes will just restart your pod indefinitely and you won't see anything.
So your last command should be :
kubectl run --generator=run-pod/v1 test-nslookup --image=busybox:1.28 -it --restart=OnFailure -- nslookup nginx-resolver-service
Why ?
Probably because of this issue.
It seems to have a delay of 5s before kubectl run actually print something.
So in order to do it without changing the restart option, you'll need to change your command like this (beware of the sleep 7, so you'll have to wait 7seconds before seeing the logs) :
kubectl run --generator=run-pod/v1 test-nslookup --image=busybox:1.28 -it --rm -- sh -c 'sleep 7; nslookup nginx-resolver-service'
I created a kubernetes cluster on my debian 9 machine using kind.
Which apparently works because I can run kubectl cluster-info with valid output.
Now I wanted to fool around with the tutorial on Learn Kubernetes Basics site.
I have already deployed the app
kubectl create deployment kubernetes-bootcamp --image=gcr.io/google-samples/kubernetes-bootcamp:v1
and started the kubectl proxy.
Output of kubectl get deployments
NAME READY UP-TO-DATE AVAILABLE AGE
kubernetes-bootcamp 1/1 1 1 17m
My problem now is: when I try to see the output of the application using curl I get
Error trying to reach service: 'dial tcp 10.244.0.5:80: connect: connection refused'
My commands
export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{.metadata.name}}{{"\n"}}{{end}}')
curl http://localhost:8001/api/v1/namespaces/default/pods/$POD_NAME/proxy/
For the sake of completeness I can run curl http://localhost:8001/api/v1/namespaces/default/pods/$POD_NAME/ and I get valid output.
The steps from this tutorial module represent environment as if You were working on one of the cluster nodes.
And the command tries to check connectivity to service locally on the node.
However In Your case by running Your kubernetes in a docker (kind) cluster the curl command is most likely ran from the host that is serving the docker containers that have kubernetes in it.
It might be possible to use docker exec to get inside kind node and try to run curl command from there.
Hope this helps.
I'm also doing following the tutorial using kind and got it to work forwarding the port:
kubectl port-forward $POD_NAME 8001:8001
Try add :8080 after the $POD_NAME
curl http://localhost:8001/api/v1/namespaces/default/pods/$POD_NAME:8080/proxy/
I'm new to using Kubernetes (v 1.11.2-gke.18), and am trying to get Sentry running as a Kubernetes deployment. This is all being run in Google Cloud. Here's the YAML files for Postgres, Redis, and Sentry:
The Redis and Postgres parts seem to be up and running just fine, but Sentry fails because: could not translate host name "postgres-sentry:5432" to address: Name or service not known.
My question is this: How do I get these services to communicate properly? How do I get the Sentry container to communicate with Postgres and Redis?
It turns out that in this case, what I needed was to change the SENTRY_REDIS_HOST and SENTRY_POSTGRES_HOST values to not have the port numbers in the env declaration. Taking those out made everything talk together as expected.
In Kubernetes pods generally can find other pods through services using DNS.
Your configuration looks correct if postgres-sentry is in the same namespace as your sentry app pod/deployment (which looks like the default namespace).
So it points that you may have a problem with DNS. You can check by shelling into the sentry app container/pod and trying to ping postgres-sentry:
$ kubectl exec -it <pod-id-of-your-sentry-app> sh
# ping postgres-sentry
Also, check if you have you /etc/resolv.conf looks something like this:
# cat /etc/resolv.conf
nameserver 10.96.0.10
search default.svc.cluster.local svc.cluster.local cluster.local
options ndots:5
Finally, check if your DNS pods are running:
$ kubectl -n kube-system get pods | grep dns
coredns-xxxxxxxxxxx-xxxxx 1/1 Running 15 116d
coredns-xxxxxxxxxxx-xxxxx 1/1 Running 15 116d