Add new plugin: external - resolve k8s ingress and LB address with external names (#2379 )

* Add new plugin: external

This plugin works in conjunction with the kubernetes plugin and exports
ingress and LB addresses as DNS records. It bypasses backend.go and
backend_lookup.go flow because it is not needed.

README, tests are implemented. The tests only exercise the unit tests,
this has not been tested in any ci.

Signed-off-by: Miek Gieben <miek@miek.nl>

* Rename to k8s_external

Signed-off-by: Miek Gieben <miek@miek.nl>

* go gen

Signed-off-by: Miek Gieben <miek@miek.nl>

2018-12-14 09:41:51 +00:00

2.2 KiB

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k8s_external

Name

k8s_external - resolve load balancer and external IPs from outside kubernetes clusters.

Description

This plugin allows an additional zone to resolve the external IP address(es) of a Kubernetes service. 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 and SRV records, all others result in NODATA responses. 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 (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 we use the dns subdomain to place the records the 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 by 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 return records you can use this extended syntax.

k8s_external [ZONE...] {
    apex APEX
    ttl TTL
}

APEX is the name (DNS label) to use the apex records, defaults to dns.
ttl allows you to set a custom TTL for responses. The default is 5 (seconds).

Examples

Enable names under example.org to be resolved to in cluster DNS addresses.

. {
   kubernetes cluster.local
   k8s_external example.org
}

Also See

For some background see resolve external IP address. And A records for services with Load Balancer IP.

Bugs

PTR queries for the reverse zone is not supported.

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