formatting Pod and Service
Signed-off-by: song <tinysong1226@gmail.com>pull/34028/head
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@ -8,8 +8,8 @@ weight: 20
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---
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<!-- overview -->
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Kubernetes creates DNS records for services and pods. You can contact
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services with consistent DNS names instead of IP addresses.
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Kubernetes creates DNS records for Services and Pods. You can contact
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Services with consistent DNS names instead of IP addresses.
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<!-- body -->
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@ -25,20 +25,20 @@ Pod's own namespace and the cluster's default domain.
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### Namespaces of Services
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A DNS query may return different results based on the namespace of the pod making
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it. DNS queries that don't specify a namespace are limited to the pod's
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namespace. Access services in other namespaces by specifying it in the DNS query.
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A DNS query may return different results based on the namespace of the Pod making
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it. DNS queries that don't specify a namespace are limited to the Pod's
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namespace. Access Services in other namespaces by specifying it in the DNS query.
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For example, consider a pod in a `test` namespace. A `data` service is in
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For example, consider a Pod in a `test` namespace. A `data` Service is in
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the `prod` namespace.
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A query for `data` returns no results, because it uses the pod's `test` namespace.
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A query for `data` returns no results, because it uses the Pod's `test` namespace.
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A query for `data.prod` returns the intended result, because it specifies the
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namespace.
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DNS queries may be expanded using the pod's `/etc/resolv.conf`. Kubelet
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sets this file for each pod. For example, a query for just `data` may be
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DNS queries may be expanded using the Pod's `/etc/resolv.conf`. Kubelet
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sets this file for each Pod. For example, a query for just `data` may be
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expanded to `data.test.svc.cluster.local`. The values of the `search` option
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are used to expand queries. To learn more about DNS queries, see
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[the `resolv.conf` manual page.](https://www.man7.org/linux/man-pages/man5/resolv.conf.5.html)
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@ -49,7 +49,7 @@ search <namespace>.svc.cluster.local svc.cluster.local cluster.local
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options ndots:5
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```
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In summary, a pod in the _test_ namespace can successfully resolve either
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In summary, a Pod in the _test_ namespace can successfully resolve either
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`data.prod` or `data.prod.svc.cluster.local`.
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### DNS Records
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@ -70,14 +70,14 @@ For more up-to-date specification, see
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### A/AAAA records
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"Normal" (not headless) Services are assigned a DNS A or AAAA record,
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depending on the IP family of the service, for a name of the form
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depending on the IP family of the Service, for a name of the form
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`my-svc.my-namespace.svc.cluster-domain.example`. This resolves to the cluster IP
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of the Service.
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"Headless" (without a cluster IP) Services are also assigned a DNS A or AAAA record,
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depending on the IP family of the service, for a name of the form
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depending on the IP family of the Service, for a name of the form
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`my-svc.my-namespace.svc.cluster-domain.example`. Unlike normal
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Services, this resolves to the set of IPs of the pods selected by the Service.
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Services, this resolves to the set of IPs of the Pods selected by the Service.
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Clients are expected to consume the set or else use standard round-robin
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selection from the set.
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@ -87,36 +87,36 @@ SRV Records are created for named ports that are part of normal or [Headless
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Services](/docs/concepts/services-networking/service/#headless-services).
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For each named port, the SRV record would have the form
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`_my-port-name._my-port-protocol.my-svc.my-namespace.svc.cluster-domain.example`.
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For a regular service, this resolves to the port number and the domain name:
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For a regular Service, this resolves to the port number and the domain name:
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`my-svc.my-namespace.svc.cluster-domain.example`.
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For a headless service, this resolves to multiple answers, one for each pod
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that is backing the service, and contains the port number and the domain name of the pod
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For a headless Service, this resolves to multiple answers, one for each Pod
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that is backing the Service, and contains the port number and the domain name of the Pod
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of the form `auto-generated-name.my-svc.my-namespace.svc.cluster-domain.example`.
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## Pods
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### A/AAAA records
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In general a pod has the following DNS resolution:
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In general a Pod has the following DNS resolution:
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`pod-ip-address.my-namespace.pod.cluster-domain.example`.
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For example, if a pod in the `default` namespace has the IP address 172.17.0.3,
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For example, if a Pod in the `default` namespace has the IP address 172.17.0.3,
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and the domain name for your cluster is `cluster.local`, then the Pod has a DNS name:
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`172-17-0-3.default.pod.cluster.local`.
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Any pods exposed by a Service have the following DNS resolution available:
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Any Pods exposed by a Service have the following DNS resolution available:
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`pod-ip-address.service-name.my-namespace.svc.cluster-domain.example`.
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### Pod's hostname and subdomain fields
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Currently when a pod is created, its hostname is the Pod's `metadata.name` value.
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Currently when a Pod is created, its hostname is the Pod's `metadata.name` value.
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The Pod spec has an optional `hostname` field, which can be used to specify the
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Pod's hostname. When specified, it takes precedence over the Pod's name to be
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the hostname of the pod. For example, given a Pod with `hostname` set to
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the hostname of the Pod. For example, given a Pod with `hostname` set to
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"`my-host`", the Pod will have its hostname set to "`my-host`".
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The Pod spec also has an optional `subdomain` field which can be used to specify
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@ -173,14 +173,14 @@ spec:
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name: busybox
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```
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If there exists a headless service in the same namespace as the pod and with
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If there exists a headless Service in the same namespace as the Pod and with
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the same name as the subdomain, the cluster's DNS Server also returns an A or AAAA
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record for the Pod's fully qualified hostname.
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For example, given a Pod with the hostname set to "`busybox-1`" and the subdomain set to
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"`default-subdomain`", and a headless Service named "`default-subdomain`" in
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the same namespace, the pod will see its own FQDN as
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the same namespace, the Pod will see its own FQDN as
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"`busybox-1.default-subdomain.my-namespace.svc.cluster-domain.example`". DNS serves an
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A or AAAA record at that name, pointing to the Pod's IP. Both pods "`busybox1`" and
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A or AAAA record at that name, pointing to the Pod's IP. Both Pods "`busybox1`" and
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"`busybox2`" can have their distinct A or AAAA records.
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The Endpoints object can specify the `hostname` for any endpoint addresses,
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@ -189,7 +189,7 @@ along with its IP.
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{{< note >}}
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Because A or AAAA records are not created for Pod names, `hostname` is required for the Pod's A or AAAA
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record to be created. A Pod with no `hostname` but with `subdomain` will only create the
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A or AAAA record for the headless service (`default-subdomain.my-namespace.svc.cluster-domain.example`),
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A or AAAA record for the headless Service (`default-subdomain.my-namespace.svc.cluster-domain.example`),
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pointing to the Pod's IP address. Also, Pod needs to become ready in order to have a
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record unless `publishNotReadyAddresses=True` is set on the Service.
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{{< /note >}}
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@ -205,17 +205,17 @@ When you set `setHostnameAsFQDN: true` in the Pod spec, the kubelet writes the P
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{{< note >}}
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In Linux, the hostname field of the kernel (the `nodename` field of `struct utsname`) is limited to 64 characters.
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If a Pod enables this feature and its FQDN is longer than 64 character, it will fail to start. The Pod will remain in `Pending` status (`ContainerCreating` as seen by `kubectl`) generating error events, such as Failed to construct FQDN from pod hostname and cluster domain, FQDN `long-FQDN` is too long (64 characters is the max, 70 characters requested). One way of improving user experience for this scenario is to create an [admission webhook controller](/docs/reference/access-authn-authz/extensible-admission-controllers/#admission-webhooks) to control FQDN size when users create top level objects, for example, Deployment.
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If a Pod enables this feature and its FQDN is longer than 64 character, it will fail to start. The Pod will remain in `Pending` status (`ContainerCreating` as seen by `kubectl`) generating error events, such as Failed to construct FQDN from Pod hostname and cluster domain, FQDN `long-FQDN` is too long (64 characters is the max, 70 characters requested). One way of improving user experience for this scenario is to create an [admission webhook controller](/docs/reference/access-authn-authz/extensible-admission-controllers/#admission-webhooks) to control FQDN size when users create top level objects, for example, Deployment.
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{{< /note >}}
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### Pod's DNS Policy
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DNS policies can be set on a per-pod basis. Currently Kubernetes supports the
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following pod-specific DNS policies. These policies are specified in the
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DNS policies can be set on a per-Pod basis. Currently Kubernetes supports the
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following Pod-specific DNS policies. These policies are specified in the
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`dnsPolicy` field of a Pod Spec.
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- "`Default`": The Pod inherits the name resolution configuration from the node
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that the pods run on.
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that the Pods run on.
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See [related discussion](/docs/tasks/administer-cluster/dns-custom-nameservers)
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for more details.
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- "`ClusterFirst`": Any DNS query that does not match the configured cluster
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@ -326,7 +326,7 @@ a list of search domains of up to 2048 characters.
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## DNS resolution on Windows nodes {#dns-windows}
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- ClusterFirstWithHostNet is not supported for pods that run on Windows nodes.
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- ClusterFirstWithHostNet is not supported for Pods that run on Windows nodes.
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Windows treats all names with a `.` as a FQDN and skips FQDN resolution.
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- On Windows, there are multiple DNS resolvers that can be used. As these come with
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slightly different behaviors, using the
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@ -335,10 +335,10 @@ a list of search domains of up to 2048 characters.
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- On Linux, you have a DNS suffix list, which is used after resolution of a name as fully
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qualified has failed.
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On Windows, you can only have 1 DNS suffix, which is the DNS suffix associated with that
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pod's namespace (example: `mydns.svc.cluster.local`). Windows can resolve FQDNs, services,
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or network name which can be resolved with this single suffix. For example, a pod spawned
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Pod's namespace (example: `mydns.svc.cluster.local`). Windows can resolve FQDNs, Services,
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or network name which can be resolved with this single suffix. For example, a Pod spawned
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in the `default` namespace, will have the DNS suffix `default.svc.cluster.local`.
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Inside a Windows pod, you can resolve both `kubernetes.default.svc.cluster.local`
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Inside a Windows Pod, you can resolve both `kubernetes.default.svc.cluster.local`
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and `kubernetes`, but not the partially qualified names (`kubernetes.default` or
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`kubernetes.default.svc`).
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