Debugging DNS has been moved to a separate article. (#7436)
* Separated
Customizing DNS service
Debugging DNS
from https://kubernetes.io/docs/tasks/administer-cluster/dns-custom-nameservers/
* fixed a typo
This commit is contained in:
Aravind
k8s-ci-robot
parent
3121977ed9
commit
06f94d3983
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@ -47,7 +47,7 @@ GEM
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jekyll-paginate (1.1.0)
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jekyll-readme-index (0.0.3)
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jekyll (~> 3.0)
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jekyll-redirect-from (0.12.1)
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jekyll-redirect-from (0.13.0)
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jekyll (~> 3.3)
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jekyll-relative-links (0.5.1)
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jekyll (~> 3.3)
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@ -145,7 +145,7 @@ DEPENDENCIES
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jekyll-optional-front-matter (~> 0.1)
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jekyll-paginate (= 1.1.0)
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jekyll-readme-index (= 0.0.3)
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jekyll-redirect-from (~> 0.11)
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jekyll-redirect-from (~> 0.13)
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jekyll-relative-links (~> 0.2)
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jekyll-seo-tag
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jekyll-sitemap
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@ -180,6 +180,7 @@ toc:
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- docs/tasks/administer-cluster/configure-multiple-schedulers.md
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- docs/tasks/administer-cluster/ip-masq-agent.md
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- docs/tasks/administer-cluster/dns-custom-nameservers.md
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- docs/tasks/administer-cluster/dns-debugging-resolution.md
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- docs/tasks/administer-cluster/pvc-protection.md
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- title: Federation - Run an App on Multiple Clusters
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@ -7,7 +7,7 @@ title: Customizing DNS Service
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{% capture overview %}
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This page provides hints on configuring DNS Pod and guidance on customizing the
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DNS resolution process and diagnosing DNS problems.
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DNS resolution process.
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{% endcapture %}
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{% capture prerequisites %}
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@ -183,182 +183,8 @@ data:
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["172.16.0.1"]
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```
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## Debugging DNS resolution
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### Create a simple Pod to use as a test environment
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Create a file named busybox.yaml with the following contents:
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{% include code.html language="yaml" file="busybox.yaml" ghlink="/docs/tasks/administer-cluster/busybox.yaml" %}
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Then create a pod using this file and verify its status:
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```shell
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$ kubectl create -f busybox.yaml
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pod "busybox" created
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$ kubectl get pods busybox
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NAME READY STATUS RESTARTS AGE
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busybox 1/1 Running 0 <some-time>
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```
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Once that pod is running, you can exec `nslookup` in that environment.
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If you see something like the following, DNS is working correctly.
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```shell
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$ kubectl exec -ti busybox -- nslookup kubernetes.default
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Server: 10.0.0.10
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Address 1: 10.0.0.10
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Name: kubernetes.default
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Address 1: 10.0.0.1
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```
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If the `nslookup` command fails, check the following:
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### Check the local DNS configuration first
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Take a look inside the resolv.conf file.
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(See [Inheriting DNS from the node](#inheriting-dns-from-the-node) and
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[Known issues](#known-issues) below for more information)
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```shell
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$ kubectl exec busybox cat /etc/resolv.conf
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```
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Verify that the search path and name server are set up like the following
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(note that search path may vary for different cloud providers):
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```
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search default.svc.cluster.local svc.cluster.local cluster.local google.internal c.gce_project_id.internal
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nameserver 10.0.0.10
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options ndots:5
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```
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Errors such as the following indicate a problem with the kube-dns add-on or
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associated Services:
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```
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$ kubectl exec -ti busybox -- nslookup kubernetes.default
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Server: 10.0.0.10
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Address 1: 10.0.0.10
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nslookup: can't resolve 'kubernetes.default'
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```
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or
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```
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$ kubectl exec -ti busybox -- nslookup kubernetes.default
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Server: 10.0.0.10
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Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local
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nslookup: can't resolve 'kubernetes.default'
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```
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### Check if the DNS pod is running
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Use the `kubectl get pods` command to verify that the DNS pod is running.
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```shell
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$ kubectl get pods --namespace=kube-system -l k8s-app=kube-dns
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NAME READY STATUS RESTARTS AGE
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...
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kube-dns-v19-ezo1y 3/3 Running 0 1h
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...
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```
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If you see that no pod is running or that the pod has failed/completed, the DNS
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add-on may not be deployed by default in your current environment and you will
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have to deploy it manually.
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### Check for Errors in the DNS pod
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Use `kubectl logs` command to see logs for the DNS daemons.
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```shell
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$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c kubedns
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$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c dnsmasq
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$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c sidecar
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```
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See if there is any suspicious log. Letter '`W`', '`E`', '`F`' at the beginning
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represent Warning, Error and Failure. Please search for entries that have these
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as the logging level and use
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[kubernetes issues](https://github.com/kubernetes/kubernetes/issues)
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to report unexpected errors.
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### Is DNS service up?
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Verify that the DNS service is up by using the `kubectl get service` command.
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```shell
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$ kubectl get svc --namespace=kube-system
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NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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...
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kube-dns 10.0.0.10 <none> 53/UDP,53/TCP 1h
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...
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```
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If you have created the service or in the case it should be created by default
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but it does not appear, see
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[debugging services](/docs/tasks/debug-application-cluster/debug-service/) for
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more information.
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### Are DNS endpoints exposed?
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You can verify that DNS endpoints are exposed by using the `kubectl get endpoints`
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command.
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```shell
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$ kubectl get ep kube-dns --namespace=kube-system
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NAME ENDPOINTS AGE
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kube-dns 10.180.3.17:53,10.180.3.17:53 1h
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```
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If you do not see the endpoints, see endpoints section in the
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[debugging services](/docs/tasks/debug-application-cluster/debug-service/) documentation.
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For additional Kubernetes DNS examples, see the
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[cluster-dns examples](https://github.com/kubernetes/examples/tree/master/staging/cluster-dns)
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in the Kubernetes GitHub repository.
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## Known issues
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Kubernetes installs do not configure the nodes' resolv.conf files to use the
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cluster DNS by default, because that process is inherently distro-specific.
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This should probably be implemented eventually.
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Linux's libc is impossibly stuck ([see this bug from
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2005](https://bugzilla.redhat.com/show_bug.cgi?id=168253)) with limits of just
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3 DNS `nameserver` records and 6 DNS `search` records. Kubernetes needs to
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consume 1 `nameserver` record and 3 `search` records. This means that if a
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local installation already uses 3 `nameserver`s or uses more than 3 `search`es,
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some of those settings will be lost. As a partial workaround, the node can run
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`dnsmasq` which will provide more `nameserver` entries, but not more `search`
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entries. You can also use kubelet's `--resolv-conf` flag.
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If you are using Alpine version 3.3 or earlier as your base image, DNS may not
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work properly owing to a known issue with Alpine.
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Check [here](https://github.com/kubernetes/kubernetes/issues/30215)
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for more information.
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## Kubernetes Federation (Multiple Zone support)
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Release 1.3 introduced Cluster Federation support for multi-site Kubernetes
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installations. This required some minor (backward-compatible) changes to the
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way the Kubernetes cluster DNS server processes DNS queries, to facilitate
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the lookup of federated services (which span multiple Kubernetes clusters).
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See the [Cluster Federation Administrators' Guide](/docs/concepts/cluster-administration/federation/)
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for more details on Cluster Federation and multi-site support.
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## References
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- [DNS for Services and Pods](/docs/concepts/services-networking/dns-pod-service/)
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- [Docs for the DNS cluster addon](http://releases.k8s.io/{{page.githubbranch}}/cluster/addons/dns/README.md)
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## What's next
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- [Autoscaling the DNS Service in a Cluster](/docs/tasks/administer-cluster/dns-horizontal-autoscaling/).
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- [Debugging DNS Resolution](/docs/tasks/administer-cluster/dns-debugging-resolution/).
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{% endcapture %}
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|
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@ -0,0 +1,197 @@
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---
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approvers:
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- bowei
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- zihongz
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title: Debugging DNS Resolution
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---
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{% capture overview %}
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This page provides hints on diagnosing DNS problems.
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{% endcapture %}
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{% capture prerequisites %}
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* {% include task-tutorial-prereqs.md %}
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* Kubernetes version 1.6 and above.
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* The cluster must be configured to use the `kube-dns` addon.
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{% endcapture %}
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{% capture steps %}
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### Create a simple Pod to use as a test environment
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Create a file named busybox.yaml with the following contents:
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{% include code.html language="yaml" file="busybox.yaml" ghlink="/docs/tasks/administer-cluster/busybox.yaml" %}
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Then create a pod using this file and verify its status:
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```shell
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$ kubectl create -f busybox.yaml
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pod "busybox" created
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$ kubectl get pods busybox
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NAME READY STATUS RESTARTS AGE
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busybox 1/1 Running 0 <some-time>
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```
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Once that pod is running, you can exec `nslookup` in that environment.
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If you see something like the following, DNS is working correctly.
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```shell
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$ kubectl exec -ti busybox -- nslookup kubernetes.default
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Server: 10.0.0.10
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Address 1: 10.0.0.10
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Name: kubernetes.default
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Address 1: 10.0.0.1
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```
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If the `nslookup` command fails, check the following:
|
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|
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### Check the local DNS configuration first
|
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|
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Take a look inside the resolv.conf file.
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(See [Inheriting DNS from the node](#inheriting-dns-from-the-node) and
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[Known issues](#known-issues) below for more information)
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```shell
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$ kubectl exec busybox cat /etc/resolv.conf
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```
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Verify that the search path and name server are set up like the following
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(note that search path may vary for different cloud providers):
|
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```
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search default.svc.cluster.local svc.cluster.local cluster.local google.internal c.gce_project_id.internal
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nameserver 10.0.0.10
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options ndots:5
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```
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Errors such as the following indicate a problem with the kube-dns add-on or
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associated Services:
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```
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$ kubectl exec -ti busybox -- nslookup kubernetes.default
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Server: 10.0.0.10
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Address 1: 10.0.0.10
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nslookup: can't resolve 'kubernetes.default'
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```
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or
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```
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$ kubectl exec -ti busybox -- nslookup kubernetes.default
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Server: 10.0.0.10
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Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local
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nslookup: can't resolve 'kubernetes.default'
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```
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### Check if the DNS pod is running
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Use the `kubectl get pods` command to verify that the DNS pod is running.
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```shell
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$ kubectl get pods --namespace=kube-system -l k8s-app=kube-dns
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NAME READY STATUS RESTARTS AGE
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...
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kube-dns-v19-ezo1y 3/3 Running 0 1h
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...
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```
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If you see that no pod is running or that the pod has failed/completed, the DNS
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add-on may not be deployed by default in your current environment and you will
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have to deploy it manually.
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|
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### Check for Errors in the DNS pod
|
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Use `kubectl logs` command to see logs for the DNS daemons.
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```shell
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$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c kubedns
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$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c dnsmasq
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$ kubectl logs --namespace=kube-system $(kubectl get pods --namespace=kube-system -l k8s-app=kube-dns -o name) -c sidecar
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```
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See if there is any suspicious log. Letter '`W`', '`E`', '`F`' at the beginning
|
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represent Warning, Error and Failure. Please search for entries that have these
|
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as the logging level and use
|
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[kubernetes issues](https://github.com/kubernetes/kubernetes/issues)
|
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to report unexpected errors.
|
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|
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### Is DNS service up?
|
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|
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Verify that the DNS service is up by using the `kubectl get service` command.
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|
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```shell
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$ kubectl get svc --namespace=kube-system
|
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NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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...
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kube-dns 10.0.0.10 <none> 53/UDP,53/TCP 1h
|
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...
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```
|
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|
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If you have created the service or in the case it should be created by default
|
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but it does not appear, see
|
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[debugging services](/docs/tasks/debug-application-cluster/debug-service/) for
|
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more information.
|
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|
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### Are DNS endpoints exposed?
|
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|
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You can verify that DNS endpoints are exposed by using the `kubectl get endpoints`
|
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command.
|
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|
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```shell
|
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$ kubectl get ep kube-dns --namespace=kube-system
|
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NAME ENDPOINTS AGE
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kube-dns 10.180.3.17:53,10.180.3.17:53 1h
|
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```
|
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|
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If you do not see the endpoints, see endpoints section in the
|
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[debugging services](/docs/tasks/debug-application-cluster/debug-service/) documentation.
|
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|
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For additional Kubernetes DNS examples, see the
|
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[cluster-dns examples](https://github.com/kubernetes/examples/tree/master/staging/cluster-dns)
|
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in the Kubernetes GitHub repository.
|
||||
|
||||
## Known issues
|
||||
|
||||
Kubernetes installs do not configure the nodes' resolv.conf files to use the
|
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cluster DNS by default, because that process is inherently distro-specific.
|
||||
This should probably be implemented eventually.
|
||||
|
||||
Linux's libc is impossibly stuck ([see this bug from
|
||||
2005](https://bugzilla.redhat.com/show_bug.cgi?id=168253)) with limits of just
|
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3 DNS `nameserver` records and 6 DNS `search` records. Kubernetes needs to
|
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consume 1 `nameserver` record and 3 `search` records. This means that if a
|
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local installation already uses 3 `nameserver`s or uses more than 3 `search`es,
|
||||
some of those settings will be lost. As a partial workaround, the node can run
|
||||
`dnsmasq` which will provide more `nameserver` entries, but not more `search`
|
||||
entries. You can also use kubelet's `--resolv-conf` flag.
|
||||
|
||||
If you are using Alpine version 3.3 or earlier as your base image, DNS may not
|
||||
work properly owing to a known issue with Alpine.
|
||||
Check [here](https://github.com/kubernetes/kubernetes/issues/30215)
|
||||
for more information.
|
||||
|
||||
## Kubernetes Federation (Multiple Zone support)
|
||||
|
||||
Release 1.3 introduced Cluster Federation support for multi-site Kubernetes
|
||||
installations. This required some minor (backward-compatible) changes to the
|
||||
way the Kubernetes cluster DNS server processes DNS queries, to facilitate
|
||||
the lookup of federated services (which span multiple Kubernetes clusters).
|
||||
See the [Cluster Federation Administrators' Guide](/docs/concepts/cluster-administration/federation/)
|
||||
for more details on Cluster Federation and multi-site support.
|
||||
|
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## References
|
||||
|
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- [DNS for Services and Pods](/docs/concepts/services-networking/dns-pod-service/)
|
||||
- [Docs for the DNS cluster addon](http://releases.k8s.io/{{page.githubbranch}}/cluster/addons/dns/README.md)
|
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|
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## What's next
|
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- [Autoscaling the DNS Service in a Cluster](/docs/tasks/administer-cluster/dns-horizontal-autoscaling/).
|
||||
|
||||
{% endcapture %}
|
||||
|
||||
{% include templates/task.md %}
|
||||
Loading…
Reference in New Issue