README ¶
kubernetes
Name
kubernetes - enables the reading zone data from a Kubernetes cluster.
Description
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 and upstreamNameservers are implemented via the proxy plugin and kubernetes upstream. See example below.
This plugin can only be used once per Server Block.
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 [URL...]
tls CERT KEY CACERT
namespaces NAMESPACE...
labels EXPRESSION
pods POD-MODE
endpoint_pod_names
upstream [ADDRESS...]
ttl TTL
transfer to ADDRESS...
fallthrough [ZONES...]
}
-
resyncperiod
specifies the Kubernetes data API DURATION period. -
endpoint
specifies the URL for a remote k8s API endpoint. If omitted, it will connect to k8s in-cluster using the cluster service account. Multiple k8s API endpoints could be specified: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...], only exposes 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 returningNXDOMAIN
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.
-
endpoint_pod_names
uses the pod name of the pod targeted by the endpoint as the endpoint name in A records, e.g.endpoint-name.my-service.namespace.svc.cluster.local. in A 1.2.3.4
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.1-2-3-4.my-service.namespace.svc.cluster.local.
) 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, use the dashed IP address form. -
upstream
[ADDRESS...] defines the upstream resolvers used for resolving services that point to external hosts (aka External Services aka CNAMEs). If no ADDRESS is given, CoreDNS will resolve External Services against itself. 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. -
noendpoints
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. -
transfer
enables zone transfers. It may be specified multiples times.To
signals the direction (onlyto
is alllow). ADDRESS must be denoted in CIDR notation (127.0.0.1/32 etc.) or just as plain addresses. The special wildcard*
means: the entire internet. Sending DNS notifies is not supported. -
fallthrough
[ZONES...] 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 [ZONES...] is omitted, then fallthrough happens for all zones for which the plugin is authoritative. If specific zones are listed (for examplein-addr.arpa
andip6.arpa
), then only queries for those zones will be subject to fallthrough. -
ignore empty_service
return 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.
Health
This plugin implements dynamic health checking. Currently this is limited to reporting healthy when the API has synced.
Watch
This plugin implements watch. A client that connects to CoreDNS using coredns/client
can be notified
of changes to A, AAAA, and SRV records for Kubernetes services and endpoints.
Examples
Handle all queries in the cluster.local
zone. Connect to Kubernetes in-cluster. Also handle all
in-addr.arpa
PTR
requests for 10.0.0.0/17
. 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:
10.0.0.0/17 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
}
stubDomains and upstreamNameservers
Here we use the proxy plugin to implement a stubDomain that forwards example.local
to the nameserver 10.100.0.10:53
.
The upstream option in kubernetes means that ExternalName services (CNAMEs) will be resolved using the respective proxy.
Also configured is an upstreamNameserver 8.8.8.8:53
that will be used for resolving names that do not fall in cluster.local
or example.local
.
.:53 {
kubernetes cluster.local {
upstream
}
proxy example.local 10.100.0.10:53
proxy . 8.8.8.8:53
}
The configuration above represents the following Kube-DNS stubDomains and upstreamNameservers configuration.
stubDomains: |
{“example.local”: [“10.100.0.10:53”]}
upstreamNameservers: |
[“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 {
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:
- endpoint in an
A
record request: endpoint.service.namespace.svc.zone, e.g.*.nginx.ns.svc.cluster.local
- service in an
A
record request: service.namespace.svc.zone, e.g.*.ns.svc.cluster.local
- namespace in an
A
record request: service.namespace.svc.zone, e.g.nginx.*.svc.cluster.local
- port and/or protocol in an
SRV
request: _port._protocol.service.namespace.svc.zone., e.g._http.*.service.ns.svc.cluster.local
- multiple wild cards are allowed in a single query, e.g.
A
Request*.*.svc.zone.
orSRV
request*.*.*.*.svc.zone.
For example, Wildcards can be used to resolve all Endpoints for a Service as A
records. e.g.: *.service.ns.svc.myzone.local
will return the Endpoint IPs in the Service service
in namespace default
:
*.service.default.svc.cluster.local. 5 IN A 192.168.10.10
*.service.default.svc.cluster.local. 5 IN A 192.168.25.15
This response can be randomized using the loadbalance
plugin
Documentation ¶
Overview ¶
Package kubernetes provides the kubernetes backend.
Index ¶
- Constants
- type 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) Health() bool
- func (k *Kubernetes) InitKubeCache() (err 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) MinTTL(state request.Request) uint32
- func (k Kubernetes) Name() string
- func (k *Kubernetes) Records(state request.Request, exact bool) ([]msg.Service, error)
- func (k *Kubernetes) RegisterKubeCache(c *caddy.Controller)
- func (k *Kubernetes) Reverse(state request.Request, exact bool, opt plugin.Options) ([]msg.Service, error)
- func (k *Kubernetes) Serial(state request.Request) uint32
- 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)
- func (k *Kubernetes) SetWatchChan(c watch.Chan)
- func (k *Kubernetes) StopWatching(qname string)
- func (k *Kubernetes) Transfer(ctx context.Context, state request.Request) (int, error)
- func (k *Kubernetes) Watch(qname string) error
Constants ¶
const ( LabelZone = "failure-domain.beta.kubernetes.io/zone" LabelRegion = "failure-domain.beta.kubernetes.io/region" )
The federation node.Labels keys used.
const ( // DNSSchemaVersion is the schema version: https://github.com/kubernetes/dns/blob/master/docs/specification.md DNSSchemaVersion = "1.0.1" // Svc is the DNS schema for kubernetes services Svc = "svc" // Pod is the DNS schema for kubernetes pods Pod = "pod" )
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type Kubernetes ¶
type Kubernetes struct { Next plugin.Handler Zones []string Upstream upstream.Upstream APIServerList []string APIProxy *apiProxy APICertAuth string APIClientCert string APIClientKey string APIConn dnsController Namespaces map[string]bool Fall fall.F TransferTo []string // 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 initialized 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 ParseStanza ¶ added in v1.0.6
func ParseStanza(c *caddy.Controller) (*Kubernetes, error)
ParseStanza parses a kubernetes stanza
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 ¶
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) Health ¶ added in v1.0.0
func (k *Kubernetes) Health() bool
Health implements the health.Healther interface.
func (*Kubernetes) InitKubeCache ¶ added in v1.0.6
func (k *Kubernetes) InitKubeCache() (err error)
InitKubeCache initializes a new Kubernetes cache.
func (*Kubernetes) IsNameError ¶
func (k *Kubernetes) IsNameError(err error) bool
IsNameError implements the ServiceBackend interface.
func (*Kubernetes) MinTTL ¶ added in v0.9.10
func (k *Kubernetes) MinTTL(state request.Request) uint32
MinTTL implements the Transferer interface.
func (*Kubernetes) RegisterKubeCache ¶ added in v1.0.6
func (k *Kubernetes) RegisterKubeCache(c *caddy.Controller)
RegisterKubeCache registers KubeCache start and stop functions with Caddy
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) Serial ¶ added in v0.9.10
func (k *Kubernetes) Serial(state request.Request) uint32
Serial implements the Transferer 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.
func (*Kubernetes) SetWatchChan ¶ added in v1.2.0
func (k *Kubernetes) SetWatchChan(c watch.Chan)
SetWatchChan implements watch.Watchable
func (*Kubernetes) StopWatching ¶ added in v1.2.0
func (k *Kubernetes) StopWatching(qname string)
StopWatching is called when no more watches remain for a name
func (*Kubernetes) Watch ¶ added in v1.2.0
func (k *Kubernetes) Watch(qname string) error
Watch is called when a watch is started for a name.