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DNS for Services and Pods
Kubernetes creates DNS records for Services and Pods. You can contact Services with consistent DNS names instead of IP addresses.
Kubernetes publishes information about Pods and Services which is used to program DNS. Kubelet configures Pods' DNS so that running containers can lookup Services by name rather than IP.
Services defined in the cluster are assigned DNS names. By default, a client Pod's DNS search list includes the Pod's own namespace and the cluster's default domain.
Namespaces of Services
A DNS query may return different results based on the namespace of the Pod making it. DNS queries that don't specify a namespace are limited to the Pod's namespace. Access Services in other namespaces by specifying it in the DNS query.
For example, consider a Pod in a
test namespace. A
data Service is in
A query for
data returns no results, because it uses the Pod's
A query for
data.prod returns the intended result, because it specifies the
DNS queries may be expanded using the Pod's
configures this file for each Pod. For example, a query for just
data may be
data.test.svc.cluster.local. The values of the
are used to expand queries. To learn more about DNS queries, see
resolv.conf manual page.
nameserver 10.32.0.10 search <namespace>.svc.cluster.local svc.cluster.local cluster.local options ndots:5
In summary, a Pod in the test namespace can successfully resolve either
What objects get DNS records?
The following sections detail the supported DNS record types and layout that is supported. Any other layout or names or queries that happen to work are considered implementation details and are subject to change without warning. For more up-to-date specification, see Kubernetes DNS-Based Service Discovery.
"Normal" (not headless) Services are assigned DNS A and/or AAAA records,
depending on the IP family or families of the Service, with a name of the form
my-svc.my-namespace.svc.cluster-domain.example. This resolves to the cluster IP
of the Service.
(without a cluster IP) Services are also assigned DNS A and/or AAAA records,
with a name of the form
my-svc.my-namespace.svc.cluster-domain.example. Unlike normal
Services, this resolves to the set of IPs of all of the Pods selected by the Service.
Clients are expected to consume the set or else use standard round-robin
selection from the set.
SRV Records are created for named ports that are part of normal or headless
services. For each named port, the SRV record has the form
For a regular Service, this resolves to the port number and the domain name:
For a headless Service, this resolves to multiple answers, one for each Pod
that is backing the Service, and contains the port number and the domain name of the Pod
of the form
In general a Pod has the following DNS resolution:
For example, if a Pod in the
default namespace has the IP address 172.17.0.3,
and the domain name for your cluster is
cluster.local, then the Pod has a DNS name:
Any Pods exposed by a Service have the following DNS resolution available:
Pod's hostname and subdomain fields
Currently when a Pod is created, its hostname (as observed from within the Pod)
is the Pod's
The Pod spec has an optional
hostname field, which can be used to specify a
different hostname. When specified, it takes precedence over the Pod's name to be
the hostname of the Pod (again, as observed from within the Pod). For example,
given a Pod with
spec.hostname set to
"my-host", the Pod will have its
hostname set to
The Pod spec also has an optional
subdomain field which can be used to indicate
that the pod is part of sub-group of the namespace. For example, a Pod with
spec.subdomain set to
"bar", in namespace
have its hostname set to
"foo" and its fully qualified domain name (FQDN) set to
"foo.bar.my-namespace.svc.cluster.local" (once more, as observed from within
If there exists a headless Service in the same namespace as the Pod, with the same name as the subdomain, the cluster's DNS Server also returns A and/or AAAA records for the Pod's fully qualified hostname.
apiVersion: v1 kind: Service metadata: name: busybox-subdomain spec: selector: name: busybox clusterIP: None ports: - name: foo # name is not required for single-port Services port: 1234 --- apiVersion: v1 kind: Pod metadata: name: busybox1 labels: name: busybox spec: hostname: busybox-1 subdomain: busybox-subdomain containers: - image: busybox:1.28 command: - sleep - "3600" name: busybox --- apiVersion: v1 kind: Pod metadata: name: busybox2 labels: name: busybox spec: hostname: busybox-2 subdomain: busybox-subdomain containers: - image: busybox:1.28 command: - sleep - "3600" name: busybox
Given the above Service
"busybox-subdomain" and the Pods which set
"busybox-subdomain", the first Pod will see its own FQDN as
"busybox-1.busybox-subdomain.my-namespace.svc.cluster-domain.example". DNS serves
A and/or AAAA records at that name, pointing to the Pod's IP. Both Pods "
busybox2" will have their own address records.
An EndpointSlice can specify the DNS hostname for any endpoint addresses, along with its IP.
hostnameis required for the Pod's A or AAAA record to be created. A Pod with no
subdomainwill only create the A or AAAA record for the headless Service (
busybox-subdomain.my-namespace.svc.cluster-domain.example), pointing to the Pods' IP addresses. Also, the Pod needs to be ready in order to have a record unless
publishNotReadyAddresses=Trueis set on the Service.
Pod's setHostnameAsFQDN field
Kubernetes v1.22 [stable]
When a Pod is configured to have fully qualified domain name (FQDN), its
hostname is the short hostname. For example, if you have a Pod with the fully
qualified domain name
then by default the
hostname command inside that Pod returns
busybox-1 and the
hostname --fqdn command returns the FQDN.
When you set
setHostnameAsFQDN: true in the Pod spec, the kubelet writes the Pod's FQDN into the hostname for that Pod's namespace. In this case, both
hostname --fqdn return the Pod's FQDN.
In Linux, the hostname field of the kernel (the
nodename field of
struct utsname) is limited to 64 characters.
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 to control FQDN size when users create top level objects, for example, Deployment.
Pod's DNS Policy
DNS policies can be set on a per-Pod basis. Currently Kubernetes supports the
following Pod-specific DNS policies. These policies are specified in the
dnsPolicy field of a Pod Spec.
Default": The Pod inherits the name resolution configuration from the node that the Pods run on. See related discussion for more details.
ClusterFirst": Any DNS query that does not match the configured cluster domain suffix, such as "
www.kubernetes.io", is forwarded to an upstream nameserver by the DNS server. Cluster administrators may have extra stub-domain and upstream DNS servers configured. See related discussion for details on how DNS queries are handled in those cases.
ClusterFirstWithHostNet": For Pods running with hostNetwork, you should explicitly set its DNS policy to "
ClusterFirstWithHostNet". Otherwise, Pods running with hostNetwork and
"ClusterFirst"will fallback to the behavior of the
- Note: This is not supported on Windows. See below for details
None": It allows a Pod to ignore DNS settings from the Kubernetes environment. All DNS settings are supposed to be provided using the
dnsConfigfield in the Pod Spec. See Pod's DNS config subsection below.
dnsPolicyis not explicitly specified, then "ClusterFirst" is used.
The example below shows a Pod with its DNS policy set to
ClusterFirstWithHostNet" because it has
hostNetwork set to
apiVersion: v1 kind: Pod metadata: name: busybox namespace: default spec: containers: - image: busybox:1.28 command: - sleep - "3600" imagePullPolicy: IfNotPresent name: busybox restartPolicy: Always hostNetwork: true dnsPolicy: ClusterFirstWithHostNet
Pod's DNS Config
Kubernetes v1.14 [stable]
Pod's DNS Config allows users more control on the DNS settings for a Pod.
dnsConfig field is optional and it can work with any
However, when a Pod's
dnsPolicy is set to "
dnsConfig field has
to be specified.
Below are the properties a user can specify in the
nameservers: a list of IP addresses that will be used as DNS servers for the Pod. There can be at most 3 IP addresses specified. When the Pod's
dnsPolicyis set to "
None", the list must contain at least one IP address, otherwise this property is optional. The servers listed will be combined to the base nameservers generated from the specified DNS policy with duplicate addresses removed.
searches: a list of DNS search domains for hostname lookup in the Pod. This property is optional. When specified, the provided list will be merged into the base search domain names generated from the chosen DNS policy. Duplicate domain names are removed. Kubernetes allows for at most 6 search domains.
options: an optional list of objects where each object may have a
nameproperty (required) and a
valueproperty (optional). The contents in this property will be merged to the options generated from the specified DNS policy. Duplicate entries are removed.
The following is an example Pod with custom DNS settings:
apiVersion: v1 kind: Pod metadata: namespace: default name: dns-example spec: containers: - name: test image: nginx dnsPolicy: "None" dnsConfig: nameservers: - 192.0.2.1 # this is an example searches: - ns1.svc.cluster-domain.example - my.dns.search.suffix options: - name: ndots value: "2" - name: edns0
When the Pod above is created, the container
test gets the following contents
nameserver 192.0.2.1 search ns1.svc.cluster-domain.example my.dns.search.suffix options ndots:2 edns0
For IPv6 setup, search path and name server should be set up like this:
kubectl exec -it dns-example -- cat /etc/resolv.conf
The output is similar to this:
nameserver 2001:db8:30::a search default.svc.cluster-domain.example svc.cluster-domain.example cluster-domain.example options ndots:5
DNS search domain list limits
Kubernetes 1.26 [beta]
Kubernetes itself does not limit the DNS Config until the length of the search domain list exceeds 32 or the total length of all search domains exceeds 2048. This limit applies to the node's resolver configuration file, the Pod's DNS Config, and the merged DNS Config respectively.
Some container runtimes of earlier versions may have their own restrictions on the number of DNS search domains. Depending on the container runtime environment, the pods with a large number of DNS search domains may get stuck in the pending state.
It is known that containerd v1.5.5 or earlier and CRI-O v1.21 or earlier have this problem.
DNS resolution on Windows nodes
- ClusterFirstWithHostNet is not supported for Pods that run on Windows nodes.
Windows treats all names with a
.as a FQDN and skips FQDN resolution.
- On Windows, there are multiple DNS resolvers that can be used. As these come with
slightly different behaviors, using the
Resolve-DNSNamepowershell cmdlet for name query resolutions is recommended.
- On Linux, you have a DNS suffix list, which is used after resolution of a name as fully
qualified has failed.
On Windows, you can only have 1 DNS suffix, which is the DNS suffix associated with that
Pod's namespace (example:
mydns.svc.cluster.local). Windows can resolve FQDNs, Services, or network name which can be resolved with this single suffix. For example, a Pod spawned in the
defaultnamespace, will have the DNS suffix
default.svc.cluster.local. Inside a Windows Pod, you can resolve both
kubernetes, but not the partially qualified names (
For guidance on administering DNS configurations, check Configure DNS Service