README
¶
k8s_external
Name
k8s_external - resolves load balancer, external IPs from outside Kubernetes clusters and if enabled headless services.
Description
This plugin allows an additional zone to resolve the external IP address(es) of a Kubernetes service and headless services. This plugin is only useful if the kubernetes plugin is also loaded.
The plugin uses an external zone to resolve in-cluster IP addresses. It only handles queries for A, AAAA, SRV, and PTR records; To make it a proper DNS zone, it handles SOA and NS queries for the apex of the zone.
By default the apex of the zone will look like the following (assuming the zone used is example.org):
example.org. 5 IN SOA ns1.dns.example.org. hostmaster.example.org. (
12345 ; serial
14400 ; refresh (4 hours)
3600 ; retry (1 hour)
604800 ; expire (1 week)
5 ; minimum (4 hours)
)
example.org 5 IN NS ns1.dns.example.org.
ns1.dns.example.org. 5 IN A ....
ns1.dns.example.org. 5 IN AAAA ....
Note that we use the dns subdomain for the records DNS needs (see the apex directive). Also
note the SOA's serial number is static. The IP addresses of the nameserver records are those of the
CoreDNS service.
The k8s_external plugin handles the subdomain dns and the apex of the zone itself; all other
queries are resolved to addresses in the cluster.
Syntax
k8s_external [ZONE...]
- ZONES zones k8s_external should be authoritative for.
If you want to change the apex domain or use a different TTL for the returned records you can use this extended syntax.
k8s_external [ZONE...] {
apex APEX
ttl TTL
}
- APEX is the name (DNS label) to use for the apex records; it defaults to
dns. ttlallows you to set a custom TTL for responses. The default is 5 (seconds).
If you want to enable headless service resolution, you can do so by adding headless option.
k8s_external [ZONE...] {
headless
}
- if there is a headless service with external IPs set, external IPs will be resolved
If the queried domain does not exist, you can fall through to next plugin by adding the fallthrough option.
k8s_external [ZONE...] {
fallthrough [ZONE...]
}
Examples
Enable names under example.org to be resolved to in-cluster DNS addresses.
. {
kubernetes cluster.local
k8s_external example.org
}
With the Corefile above, the following Service will get an A record for test.default.example.org with the IP address 192.168.200.123.
apiVersion: v1
kind: Service
metadata:
name: test
namespace: default
spec:
clusterIP: None
externalIPs:
- 192.168.200.123
type: ClusterIP
The k8s_external plugin can be used in conjunction with the transfer plugin to enable zone transfers. Notifies are not supported.
. {
transfer example.org {
to *
}
kubernetes cluster.local
k8s_external example.org
}
With the fallthrough option, if the queried domain does not exist, it will be passed to the next plugin that matches the zone.
. {
kubernetes cluster.local
k8s_external example.org {
fallthrough
}
forward . 8.8.8.8
}
See Also
For some background see resolve external IP address. And A records for services with Load Balancer IP.
Documentation
¶
Overview ¶
Package external implements external names for kubernetes clusters.
This plugin only handles three qtypes (except the apex queries, because those are handled differently). We support A, AAAA and SRV request, for all other types we return NODATA or NXDOMAIN depending on the state of the cluster.
A plugin willing to provide these services must implement the Externaler interface, although it likely only makes sense for the *kubernetes* plugin.
Index ¶
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
This section is empty.
Types ¶
type External ¶
type External struct {
Next plugin.Handler
Zones []string
Fall fall.F
// contains filtered or unexported fields
}
External serves records for External IPs and Loadbalance IPs of Services in Kubernetes clusters.
type Externaler ¶
type Externaler interface {
// External returns a slice of msg.Services that are looked up in the backend and match
// the request.
External(request.Request, bool) ([]msg.Service, int)
// ExternalAddress should return a string slice of addresses for the nameserving endpoint.
ExternalAddress(state request.Request, headless bool) []dns.RR
// ExternalServices returns all services in the given zone as a slice of msg.Service and if enabled, headless services as a map of services.
ExternalServices(zone string, headless bool) ([]msg.Service, map[string][]msg.Service)
// ExternalSerial gets the current serial.
ExternalSerial(string) uint32
}
Externaler defines the interface that a plugin should implement in order to be used by External.
Source Files