dns/man/coredns-kubernetes.7

.\" Generated by Mmark Markdown Processer - mmark.miek.nl
.TH "COREDNS-KUBERNETES" 7 "March 2026" "CoreDNS" "CoreDNS Plugins"

.SH "NAME"
.PP
\fIkubernetes\fP - enables reading zone data from a Kubernetes cluster.

.SH "DESCRIPTION"
.PP
This plugin implements the Kubernetes DNS-Based Service Discovery
Specification
\[la]https://github.com/kubernetes/dns/blob/master/docs/specification.md\[ra].

.PP
CoreDNS running the kubernetes plugin can be used as a replacement for kube-dns in a kubernetes
cluster.  See the deployment
\[la]https://github.com/coredns/deployment\[ra] repository for details on how
to deploy CoreDNS in Kubernetes
\[la]https://github.com/coredns/deployment/tree/master/kubernetes\[ra].

.PP
stubDomains and upstreamNameservers
\[la]https://kubernetes.io/blog/2017/04/configuring-private-dns-zones-upstream-nameservers-kubernetes/\[ra]
are implemented via the \fIforward\fP plugin. See the examples below.

.PP
This plugin can only be used once per Server Block.

.SH "SYNTAX"
.PP
.RS

.nf
kubernetes [ZONES...]

.fi
.RE

.PP
With only the plugin specified, the \fIkubernetes\fP plugin will default to the zone specified in
the server's block. It will handle all queries in that zone and connect to Kubernetes in-cluster. It
will not provide PTR records for services or A records for pods. If \fBZONES\fP is used it specifies
all the zones the plugin should be authoritative for.

.PP
.RS

.nf
kubernetes [ZONES...] {
    endpoint URL
    tls CERT KEY CACERT
    kubeconfig KUBECONFIG [CONTEXT]
    apiserver\_qps QPS
    apiserver\_burst BURST
    apiserver\_max\_inflight MAX
    namespaces NAMESPACE...
    labels EXPRESSION
    pods POD\-MODE
    endpoint\_pod\_names
    ttl TTL
    noendpoints
    fallthrough [ZONES...]
    ignore empty\_service
    multicluster [ZONES...]
    startup\_timeout DURATION
}

.fi
.RE

.IP \(bu 4
\fB\fCendpoint\fR specifies the \fBURL\fP for a remote k8s API endpoint.
If omitted, it will connect to k8s in-cluster using the cluster service account. Needs \fB\fCtls\fR for clusters with authentication.
This option is ignored if \fB\fCkubeconfig\fR is set.
.IP \(bu 4
\fB\fCtls\fR \fBCERT\fP \fBKEY\fP \fBCACERT\fP are the TLS cert, key and the CA cert file names for remote k8s connection.
This option is ignored if connecting in-cluster (i.e. endpoint is not specified).
.IP \(bu 4
\fB\fCkubeconfig\fR \fBKUBECONFIG [CONTEXT]\fP authenticates the connection to a remote k8s cluster using a kubeconfig file.
\fB[CONTEXT]\fP is optional, if not set, then the current context specified in kubeconfig will be used.
It supports TLS, username and password, or token-based authentication.
This option is ignored if omitted. The cluster address in the \fB\fCkubeconfig\fR is given preference.
.IP \(bu 4
\fB\fCapiserver_qps\fR \fBQPS\fP sets the maximum queries per second (QPS) rate limit for requests.
This allows you to control the rate at which the plugin sends requests to the API server to prevent overwhelming it.
.IP \(bu 4
\fB\fCapiserver_burst\fR \fBBURST\fP sets the maximum burst size for requests.
This allows temporary spikes in request rate up to this value, even if it exceeds the QPS limit.
.IP \(bu 4
\fB\fCapiserver_max_inflight\fR \fBMAX\fP sets the maximum number of concurrent in-flight requests.
This caps the total number of simultaneous requests the plugin can make to the API server.
.IP \(bu 4
\fB\fCnamespaces\fR \fBNAMESPACE [NAMESPACE...]\fP only exposes the k8s namespaces listed.
If this option is omitted all namespaces are exposed
.IP \(bu 4
\fB\fCnamespace_labels\fR \fBEXPRESSION\fP only expose the records for Kubernetes namespaces that match this label selector.
The label selector syntax is described in the
Kubernetes User Guide - Labels
\[la]https://kubernetes.io/docs/user-guide/labels/\[ra]. An example that
only exposes namespaces labeled as "istio-injection=enabled", would use:
\fB\fClabels istio-injection=enabled\fR.
.IP \(bu 4
\fB\fClabels\fR \fBEXPRESSION\fP only exposes the records for Kubernetes objects that match this label selector.
The label selector syntax is described in the
Kubernetes User Guide - Labels
\[la]https://kubernetes.io/docs/user-guide/labels/\[ra]. An example that
only exposes objects labeled as "application=nginx" in the "staging" or "qa" environments, would
use: \fB\fClabels environment in (staging, qa),application=nginx\fR.
.IP \(bu 4
\fB\fCpods\fR \fBPOD-MODE\fP sets the mode for handling IP-based pod A records, e.g.
\fB\fC1-2-3-4.ns.pod.cluster.local. in A 1.2.3.4\fR.
This option is provided to facilitate use of SSL certs when connecting directly to pods. Valid
values for \fBPOD-MODE\fP:

.RS
.IP \(en 4
\fB\fCdisabled\fR: Default. Do not process pod requests, always returning \fB\fCNXDOMAIN\fR
.IP \(en 4
\fB\fCinsecure\fR: Always return an A record with IP from request (without checking k8s).  This option
is vulnerable to abuse if used maliciously in conjunction with wildcard SSL certs.  This
option is provided for backward compatibility with kube-dns.
.IP \(en 4
\fB\fCverified\fR: Return an A record if there exists a pod in same namespace with matching IP.  This
option requires substantially more memory than in insecure mode, since it will maintain a watch
on all pods.

.RE
.IP \(bu 4
\fB\fCendpoint_pod_names\fR uses the pod name of the pod targeted by the endpoint as
the endpoint name in A records, e.g.,
\fB\fCendpoint-name.my-service.namespace.svc.cluster.local. in A 1.2.3.4\fR
By default, the endpoint-name name selection is as follows: Use the hostname
of the endpoint, or if hostname is not set, use the dashed form of the endpoint
IP address (e.g., \fB\fC1-2-3-4.my-service.namespace.svc.cluster.local.\fR)
If this directive is included, then name selection for endpoints changes as
follows: Use the hostname of the endpoint, or if hostname is not set, use the
pod name of the pod targeted by the endpoint. If there is no pod targeted by
the endpoint or pod name is longer than 63, use the dashed IP address form.
.IP \(bu 4
\fB\fCttl\fR allows you to set a custom TTL for responses. The default is 5 seconds.  The minimum TTL allowed is
0 seconds, and the maximum is capped at 3600 seconds. Setting TTL to 0 will prevent records from being cached.
.IP \(bu 4
\fB\fCnoendpoints\fR will turn off the serving of endpoint records by disabling the watch on endpoints.
All endpoint queries and headless service queries will result in an NXDOMAIN.
.IP \(bu 4
\fB\fCfallthrough\fR \fB[ZONES...]\fP If a query for a record in the zones for which the plugin is authoritative
results in NXDOMAIN, normally that is what the response will be. However, if you specify this option,
the query will instead be passed on down the plugin chain, which can include another plugin to handle
the query. If \fB[ZONES...]\fP is omitted, then fallthrough happens for all zones for which the plugin
is authoritative. If specific zones are listed (for example \fB\fCin-addr.arpa\fR and \fB\fCip6.arpa\fR), then only
queries for those zones will be subject to fallthrough.
.IP \(bu 4
\fB\fCignore empty_service\fR returns NXDOMAIN for services without any ready endpoint addresses (e.g., ready pods).
This allows the querying pod to continue searching for the service in the search path.
The search path could, for example, include another Kubernetes cluster.
.IP \(bu 4
\fB\fCmulticluster\fR defines the multicluster zones as defined by Multi-Cluster
Services API (MCS-API). Specifying this option is generally paired with the
installation of an MCS-API implementation and the ServiceImport and ServiceExport
CRDs. The plugin MUST be authoritative for the zones listed here.
.IP \(bu 4
\fB\fCstartup_timeout\fR specifies the \fBDURATION\fP value that limits the time to wait for informer cache synced
when the kubernetes plugin starts. If not specified, the default timeout will be 5s.


.PP
Enabling zone transfer is done by using the \fItransfer\fP plugin.

.SH "STARTUP"
.PP
When CoreDNS starts with the \fIkubernetes\fP plugin enabled, it will delay serving DNS for up to 5 seconds
until it can connect to the Kubernetes API and synchronize all object watches.  If this cannot happen within
5 seconds, then CoreDNS will start serving DNS while the \fIkubernetes\fP plugin continues to try to connect
and synchronize all object watches.  CoreDNS will answer SERVFAIL to any request made for a Kubernetes record
that has not yet been synchronized. You can also determine how long to wait by specifying \fB\fCstartup_timeout\fR.

.SH "MONITORING KUBERNETES ENDPOINTS"
.PP
The \fIkubernetes\fP plugin watches Endpoints via the \fB\fCdiscovery.EndpointSlices\fR API.

.SH "READY"
.PP
This plugin reports readiness to the ready plugin. This will happen after it has synced to the
Kubernetes API.

.SH "PTR RECORDS"
.PP
This plugin creates PTR records for every Pod selected by a Service. If a given Pod is selected by more than
one Service a separate PTR record will exist for each Service selecting it.

.SH "EXAMPLES"
.PP
Handle all queries in the \fB\fCcluster.local\fR zone. Connect to Kubernetes in-cluster. Also handle all
\fB\fCin-addr.arpa\fR \fB\fCPTR\fR requests for \fB\fC10.0.0.0/17\fR . Verify the existence of pods when answering pod
requests.

.PP
.RS

.nf
10.0.0.0/17 cluster.local {
    kubernetes {
        pods verified
    }
}

.fi
.RE

.PP
Or you can selectively expose some namespaces:

.PP
.RS

.nf
kubernetes cluster.local {
    namespaces test staging
}

.fi
.RE

.PP
Connect to Kubernetes with CoreDNS running outside the cluster:

.PP
.RS

.nf
kubernetes cluster.local {
    endpoint https://k8s\-endpoint:8443
    tls cert key cacert
}

.fi
.RE

.PP
Configure multicluster

.PP
.RS

.nf
kubernetes cluster.local clusterset.local {
    multicluster clusterset.local
}

.fi
.RE

.SH "STUBDOMAINS AND UPSTREAMNAMESERVERS"
.PP
Here we use the \fIforward\fP plugin to implement a stubDomain that forwards \fB\fCexample.local\fR to the nameserver \fB\fC10.100.0.10:53\fR.
Also configured is an upstreamNameserver \fB\fC8.8.8.8:53\fR that will be used for resolving names that do not fall in \fB\fCcluster.local\fR
or \fB\fCexample.local\fR.

.PP
.RS

.nf
cluster.local:53 {
    kubernetes cluster.local
}
example.local {
    forward . 10.100.0.10:53
}

\&. {
    forward . 8.8.8.8:53
}

.fi
.RE

.PP
The configuration above represents the following Kube-DNS stubDomains and upstreamNameservers configuration.

.PP
.RS

.nf
stubDomains: |
   {“example.local”: [“10.100.0.10:53”]}
upstreamNameservers: |
   [“8.8.8.8:53”]

.fi
.RE

.SH "AUTOPATH"
.PP
The \fIkubernetes\fP plugin can be used in conjunction with the \fIautopath\fP plugin.  Using this
feature enables server-side domain search path completion in Kubernetes clusters.  Note: \fB\fCpods\fR must
be set to \fB\fCverified\fR for this to function properly. Furthermore, the remote IP address in the DNS
packet received by CoreDNS must be the IP address of the Pod that sent the request.

.PP
.RS

.nf
cluster.local {
    autopath @kubernetes
    kubernetes {
        pods verified
    }
}

.fi
.RE

.SH "METADATA"
.PP
The kubernetes plugin will publish the following metadata, if the \fImetadata\fP
plugin is also enabled:

.IP \(bu 4
\fB\fCkubernetes/endpoint\fR: the endpoint name in the query
.IP \(bu 4
\fB\fCkubernetes/kind\fR: the resource kind (pod or svc) in the query
.IP \(bu 4
\fB\fCkubernetes/namespace\fR: the namespace in the query
.IP \(bu 4
\fB\fCkubernetes/port-name\fR: the port name in an SRV query
.IP \(bu 4
\fB\fCkubernetes/protocol\fR: the protocol in an SRV query
.IP \(bu 4
\fB\fCkubernetes/service\fR: the service name in the query
.IP \(bu 4
\fB\fCkubernetes/client-namespace\fR: the client pod's namespace (see requirements below)
.IP \(bu 4
\fB\fCkubernetes/client-pod-name\fR: the client pod's name (see requirements below)
.IP \(bu 4
\fB\fCkubernetes/client-label/<label key>\fR: a label on the client pod (see requirements below)


.PP
The \fB\fCkubernetes/client-namespace\fR, \fB\fCkubernetes/client-pod-name\fR, and \fB\fCkubernetes/client-label/<label key>\fR
metadata work by reconciling the client IP address in the DNS request packet to a known pod IP address.
Therefore the following is required:
 * \fB\fCpods verified\fR mode must be enabled
 * the remote IP address in the DNS packet received by CoreDNS must be the IP address
   of the Pod that sent the request.

.SH "METRICS"
.PP
If monitoring is enabled (via the \fIprometheus\fP plugin) then the following metrics are exported:

.IP \(bu 4
\fB\fCcoredns_kubernetes_dns_programming_duration_seconds{service_kind}\fR - Exports the
DNS programming latency SLI
\[la]https://github.com/kubernetes/community/blob/master/sig-scalability/slos/dns_programming_latency.md\[ra].
The metrics has the \fB\fCservice_kind\fR label that identifies the kind of the
kubernetes service
\[la]https://kubernetes.io/docs/concepts/services-networking/service\[ra].
It may take one of the three values:

.RS
.IP \(en 4
\fB\fCcluster_ip\fR
.IP \(en 4
\fB\fCheadless_with_selector\fR
.IP \(en 4
\fB\fCheadless_without_selector\fR

.RE


.PP
The following are client level metrics to monitor apiserver request latency & status codes. \fB\fCverb\fR identifies the apiserver request type
\[la]https://kubernetes.io/docs/reference/using-api/api-concepts/#single-resource-api\[ra] and \fB\fChost\fR denotes the apiserver endpoint.
* \fB\fCcoredns_kubernetes_rest_client_request_duration_seconds{verb, host}\fR - captures apiserver request latency perceived by client grouped by \fB\fCverb\fR and \fB\fChost\fR.
* \fB\fCcoredns_kubernetes_rest_client_rate_limiter_duration_seconds{verb, host}\fR - captures apiserver request latency contributed by client side rate limiter grouped by \fB\fCverb\fR & \fB\fChost\fR.
* \fB\fCcoredns_kubernetes_rest_client_requests_total{method, code, host}\fR - captures total apiserver requests grouped by \fB\fCmethod\fR, \fB\fCstatus_code\fR & \fB\fChost\fR.

.SH "BUGS"
.PP
The duration metric does not yet support the \fB\fCheadless_without_selector\fR service kind.

.SH "SEE ALSO"
.PP
See the \fIautopath\fP plugin to enable search path optimizations. And use the \fItransfer\fP plugin to
enable outgoing zone transfers.