kubernetes

README

kubernetes

The kubernetes plugin enables the reading zone data from a Kubernetes cluster. It implements the Kubernetes DNS-Based Service Discovery Specification.

CoreDNS running the kubernetes plugin can be used as a replacement of kube-dns in a kubernetes cluster. See the deployment repository for details on how to deploy CoreDNS in Kubernetes.

stubDomains are implemented via the proxy plugin.

Syntax

kubernetes [ZONES...]

With only the directive specified, the kubernetes 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 ZONES is used it specifies all the zones the plugin should be authoritative for.

kubernetes [ZONES...] {
    resyncperiod DURATION
    endpoint URL
    tls CERT KEY CACERT
    namespaces NAMESPACE...
    labels EXPRESSION
    pods POD-MODE
    upstream ADDRESS...
    ttl TTL
    fallthrough
}

• resyncperiod specifies the Kubernetes data API DURATION period.

• endpoint specifies the URL for a remove k8s API endpoint. If omitted, it will connect to k8s in-cluster using the cluster service account. Multiple k8s API endpoints could be specified, separated by ,s, e.g. endpoint http://k8s-endpoint1:8080,http://k8s-endpoint2:8080. CoreDNS will automatically perform a healthcheck and proxy to the healthy k8s API endpoint.

• tls CERT KEY CACERT 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).

• namespaces NAMESPACE [NAMESPACE...], exposed only the k8s namespaces listed. If this option is omitted all namespaces are exposed

• labels EXPRESSION only exposes the records for Kubernetes objects that match this label selector. The label selector syntax is described in the Kubernetes User Guide - Labels. An example that only exposes objects labeled as "application=nginx" in the "staging" or "qa" environments, would use: labels environment in (staging, qa),application=nginx.

• pods POD-MODE sets the mode for handling IP-based pod A records, e.g. 1-2-3-4.ns.pod.cluster.local. in A 1.2.3.4. This option is provided to facilitate use of SSL certs when connecting directly to pods. Valid values for POD-MODE:

  • disabled: Default. Do not process pod requests, always returning NXDOMAIN
  • insecure: Always return an A record with IP from request (without checking k8s). This option is is vulnerable to abuse if used maliciously in conjunction with wildcard SSL certs. This option is provided for backward compatibility with kube-dns.
  • verified: 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.

• upstream ADDRESS [ADDRESS...] defines the upstream resolvers used for resolving services that point to external hosts (External Services). ADDRESS can be an ip, an ip:port, or a path to a file structured like resolv.conf.

• ttl allows you to set a custom TTL for responses. The default (and allowed minimum) is to use 5 seconds, the maximum is capped at 3600 seconds.

• fallthrough If a query for a record in the cluster zone 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.

Examples

Handle all queries in the cluster.local zone. Connect to Kubernetes in-cluster. Also handle all PTR requests for 10.0.0.0/16 . Verify the existence of pods when answering pod requests. Resolve upstream records against 10.102.3.10. Note we show the entire server block here:

10.0.0.0/16 cluster.local {
    kubernetes {
        pods verified
        upstream 10.102.3.10:53
    }
}

Or you can selectively expose some namespaces:

kubernetes cluster.local {
    namespaces test staging
}

Connect to Kubernetes with CoreDNS running outside the cluster:

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

Here we use the proxy plugin to implement stubDomains that forwards example.org and example.com to another nameserver.

cluster.local {
    kubernetes {
        endpoint https://k8s-endpoint:8443
        tls cert key cacert
    }
}
example.org {
    proxy . 8.8.8.8:53
}
example.com {
    proxy . 8.8.8.8:53
}

AutoPath

The kubernetes plugin can be used in conjunction with the autopath plugin. Using this feature enables server-side domain search path completion in kubernetes clusters. Note: pods must be set to verified for this to function properly.

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

Federation

The kubernetes plugin can be used in conjunction with the federation plugin. Using this feature enables serving federated domains from the kubernetes clusters.

cluster.local {
    federation {
        fallthrough
        prod prod.example.org
        staging staging.example.org

    }
    kubernetes
}

Wildcards

Some query labels accept a wildcard value to match any value. If a label is a valid wildcard (*, or the word "any"), then that label will match all values. The labels that accept wildcards are:

• service in an A record request: service.namespace.svc.zone.
  • e.g. *.ns.svc.myzone.local
• namespace in an A record request: service.namespace.svc.zone.
  • e.g. nginx.*.svc.myzone.local
• port and/or protocol in an SRV request: _port._protocol.service.namespace.svc.zone.
  • e.g. _http.*.service.ns.svc.
• multiple wild cards are allowed in a single query.
  • e.g. A Request *.*.svc.zone. or SRV request *.*.*.*.svc.zone.

Documentation

Overview

Package kubernetes provides the kubernetes backend.

Index

• Constants
• type Kubernetes
  • func New(zones []string) *Kubernetes
  • func (k *Kubernetes) AutoPath(state request.Request) []string
  • func (k *Kubernetes) Federations(state request.Request, fname, fzone string) (msg.Service, error)
  • func (k *Kubernetes) IsNameError(err error) bool
  • func (k *Kubernetes) Lookup(state request.Request, name string, typ uint16) (*dns.Msg, error)
  • func (k Kubernetes) Name() string
  • func (k *Kubernetes) Records(state request.Request, exact bool) ([]msg.Service, error)
  • func (k *Kubernetes) Reverse(state request.Request, exact bool, opt plugin.Options) ([]msg.Service, error)
  • func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error)
  • func (k *Kubernetes) Services(state request.Request, exact bool, opt plugin.Options) (svcs []msg.Service, err error)

Constants

const (
	LabelZone   = "failure-domain.beta.kubernetes.io/zone"
	LabelRegion = "failure-domain.beta.kubernetes.io/region"
)

The federation node.Labels keys used.

const (
	// Svc is the DNS schema for kubernetes services
	Svc = "svc"
	// Pod is the DNS schema for kubernetes pods
	Pod = "pod"
)

const (

	// DNSSchemaVersion is the schema version: https://github.com/kubernetes/dns/blob/master/docs/specification.md
	DNSSchemaVersion = "1.0.1"
)

Types

type Kubernetes

type Kubernetes struct {
	Next          plugin.Handler
	Zones         []string
	Proxy         proxy.Proxy // Proxy for looking up names during the resolution process
	APIServerList []string
	APIProxy      *apiProxy
	APICertAuth   string
	APIClientCert string
	APIClientKey  string
	APIConn       dnsController
	Namespaces    map[string]bool

	Fallthrough bool
	// contains filtered or unexported fields
}

Kubernetes implements a plugin that connects to a Kubernetes cluster.

func New

func New(zones []string) *Kubernetes

New returns a intialized Kubernetes. It default interfaceAddrFunc to return 127.0.0.1. All other values default to their zero value, primaryZoneIndex will thus point to the first zone.

func (*Kubernetes) AutoPath

func (k *Kubernetes) AutoPath(state request.Request) []string

AutoPath implements the AutoPathFunc call from the autopath plugin. It returns a per-query search path or nil indicating no searchpathing should happen.

func (*Kubernetes) Federations

func (k *Kubernetes) Federations(state request.Request, fname, fzone string) (msg.Service, error)

Federations is used from the federations plugin to return the service that should be returned as a CNAME for federation(s) to work.

func (*Kubernetes) IsNameError

func (k *Kubernetes) IsNameError(err error) bool

IsNameError implements the ServiceBackend interface.

func (*Kubernetes) Lookup

func (k *Kubernetes) Lookup(state request.Request, name string, typ uint16) (*dns.Msg, error)

Lookup implements the ServiceBackend interface.

func (Kubernetes) Name

func (k Kubernetes) Name() string

Name implements the Handler interface.

func (*Kubernetes) Records

func (k *Kubernetes) Records(state request.Request, exact bool) ([]msg.Service, error)

Records looks up services in kubernetes.

func (*Kubernetes) Reverse

func (k *Kubernetes) Reverse(state request.Request, exact bool, opt plugin.Options) ([]msg.Service, error)

Reverse implements the ServiceBackend interface.

func (Kubernetes) ServeDNS

func (k Kubernetes) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) (int, error)

ServeDNS implements the plugin.Handler interface.

func (*Kubernetes) Services

func (k *Kubernetes) Services(state request.Request, exact bool, opt plugin.Options) (svcs []msg.Service, err error)

Services implements the ServiceBackend interface.