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}, `Configure the environment variable `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `DOMAIN`), ` to a fully qualified domain name (FQDN) that the host should be able to resolve (`, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `www.google.com`), ` is used as an example) and run the following command to let each container on every host resolve the configured domain name (it's a single line command).`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", {
parentName: "li"
}, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `export DOMAIN=www.google.com; echo "=> Start DNS resolve test"; kubectl get pods -l name=dnstest --no-headers -o custom-columns=NAME:.metadata.name,HOSTIP:.status.hostIP | while read pod host; do kubectl exec $pod -- /bin/sh -c "nslookup $DOMAIN > /dev/null 2>&1"; RC=$?; if [ $RC -ne 0 ]; then echo $host cannot resolve $DOMAIN; fi; done; echo "=> End DNS resolve test"
`))), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("li", {
parentName: "ol"
}, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", {
parentName: "li"
}, `When this command has finished running, the output indicating everything is correct is:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", {
parentName: "li"
}, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `=> Start DNS resolve test
=> End DNS resolve test
`)))), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `If you see error in the output, that means that the mentioned host(s) is/are not able to resolve the given FQDN.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `Example error output of a situation where host with IP 209.97.182.150 had the UDP ports blocked.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `=> Start DNS resolve test
command terminated with exit code 1
209.97.182.150 cannot resolve www.google.com
=> End DNS resolve test
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `Cleanup the alpine DaemonSet by running `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `kubectl delete ds/dnstest`), `.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("h3", {
"id": "coredns-specific"
}, `CoreDNS specific`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("h4", {
"id": "check-coredns-logging"
}, `Check CoreDNS logging`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `kubectl -n kube-system logs -l k8s-app=kube-dns
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("h4", {
"id": "check-configuration"
}, `Check configuration`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `CoreDNS configuration is stored in the configmap `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `coredns`), ` in the `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `kube-system`), ` namespace.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `kubectl -n kube-system get configmap coredns -o go-template={{.data.Corefile}}
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("h4", {
"id": "check-upstream-nameservers-in-resolvconf"
}, `Check upstream nameservers in resolv.conf`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `By default, the configured nameservers on the host (in `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/etc/resolv.conf`), `) will be used as upstream nameservers for CoreDNS. You can check this file on the host or run the following Pod with `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `dnsPolicy`), ` set to `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `Default`), `, which will inherit the `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/etc/resolv.conf`), ` from the host it is running on.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `kubectl run -i --restart=Never --rm test-\${RANDOM} --image=ubuntu --overrides='{"kind":"Pod", "apiVersion":"v1", "spec": {"dnsPolicy":"Default"}}' -- sh -c 'cat /etc/resolv.conf'
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("h4", {
"id": "enable-query-logging"
}, `Enable query logging`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `Enabling query logging can be done by enabling the `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("a", {
parentName: "p",
"href": "https://coredns.io/plugins/log/"
}, `log plugin`), ` in the Corefile configuration in the configmap `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `coredns`), `. You can do so by using `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `kubectl -n kube-system edit configmap coredns`), ` or use the command below to replace the configuration in place:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `kubectl get configmap -n kube-system coredns -o json | sed -e 's_loadbalance_log\\\\n loadbalance_g' | kubectl apply -f -
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `All queries will now be logged and can be checked using the command in `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("a", {
parentName: "p",
"href": "#check-coredns-logging"
}, `Check CoreDNS logging`), `.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("h3", {
"id": "kube-dns-specific"
}, `kube-dns specific`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("h4", {
"id": "check-upstream-nameservers-in-kubedns-container"
}, `Check upstream nameservers in kubedns container`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `By default, the configured nameservers on the host (in `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/etc/resolv.conf`), `) will be used as upstream nameservers for kube-dns. Sometimes the host will run a local caching DNS nameserver, which means the address in `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/etc/resolv.conf`), ` will point to an address in the loopback range (`, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `127.0.0.0/8`), `) which will be unreachable by the container. In case of Ubuntu 18.04, this is done by `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `systemd-resolved`), `. We detect if `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `systemd-resolved`), ` is running, and will automatically use the `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/etc/resolv.conf`), ` file with the correct upstream nameservers (which is located at `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/run/systemd/resolve/resolv.conf`), `).`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `Use the following command to check the upstream nameservers used by the kubedns container:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `kubectl -n kube-system get pods -l k8s-app=kube-dns --no-headers -o custom-columns=NAME:.metadata.name,HOSTIP:.status.hostIP | while read pod host; do echo "Pod \${pod} on host \${host}"; kubectl -n kube-system exec $pod -c kubedns cat /etc/resolv.conf; done
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `Example output:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `Pod kube-dns-667c7cb9dd-z4dsf on host x.x.x.x
nameserver 1.1.1.1
nameserver 8.8.4.4
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `If the output shows an address in the loopback range (`, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `127.0.0.0/8`), `), you can correct this in two ways:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("ul", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("li", {
parentName: "ul"
}, `Make sure the correct nameservers are listed in `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "li"
}, `/etc/resolv.conf`), ` on your nodes in the cluster, please consult your operating system documentation on how to do this. Make sure you execute this before provisioning a cluster, or reboot the nodes after making the modification.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("li", {
parentName: "ul"
}, `Configure the `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "li"
}, `kubelet`), ` to use a different file for resolving names, by using `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "li"
}, `extra_args`), ` as shown below (where `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "li"
}, `/run/resolvconf/resolv.conf`), ` is the file with the correct nameservers):`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `services:
kubelet:
extra_args:
resolv-conf: "/run/resolvconf/resolv.conf"
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("admonition", {
"type": "note"
}, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", {
parentName: "admonition"
}, `As the `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `kubelet`), ` is running inside a container, the path for files located in `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/etc`), ` and `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/usr`), ` are in `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/host/etc`), ` and `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `/host/usr`), ` inside the `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("inlineCode", {
parentName: "p"
}, `kubelet`), ` container.`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `See `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("a", {
parentName: "p",
"href": "/v2.9/reference-guides/cluster-configuration/rancher-server-configuration/rke1-cluster-configuration#editing-clusters-with-yaml"
}, `Editing Cluster as YAML`), ` how to apply this change. When the provisioning of the cluster has finished, you have to remove the kube-dns pod to activate the new setting in the pod:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `kubectl delete pods -n kube-system -l k8s-app=kube-dns
pod "kube-dns-5fd74c7488-6pwsf" deleted
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `Try to resolve name again using `, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("a", {
parentName: "p",
"href": "#check-if-domain-names-are-resolving"
}, `Check if domain names are resolving`), `.`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `If you want to check the kube-dns configuration in your cluster (for example, to check if there are different upstream nameservers configured), you can run the following command to list the kube-dns configuration:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `kubectl -n kube-system get configmap kube-dns -o go-template='{{range $key, $value := .data}}{{ $key }}{{":"}}{{ $value }}{{"\\n"}}{{end}}'
`)), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("p", null, `Example output:`), /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("pre", null, /*#__PURE__*/ (0,_mdx_js_react__WEBPACK_IMPORTED_MODULE_1__/* .mdx */ .kt)("code", {
parentName: "pre"
}, `upstreamNameservers:["1.1.1.1"]
`)));
}
MDXContent.isMDXComponent = true;
/***/ })
}]);
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