47dceabfc6
* Add fallthrough option to k8s_external plugin to allow transitioning control to the next plugin if the domain is not found * Exit on start up if required plugin is not present. Signed-off-by: vanceli <vanceli@tencent.com> --------- Signed-off-by: vanceli <vanceli@tencent.com> Co-authored-by: vanceli <vanceli@tencent.com>
132 lines
3.4 KiB
Markdown
132 lines
3.4 KiB
Markdown
# k8s_external
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## Name
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*k8s_external* - resolves load balancer, external IPs from outside Kubernetes clusters and if enabled headless services.
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## Description
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This plugin allows an additional zone to resolve the external IP address(es) of a Kubernetes
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service and headless services. This plugin is only useful if the *kubernetes* plugin is also loaded.
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The plugin uses an external zone to resolve in-cluster IP addresses. It only handles queries for A,
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AAAA, SRV, and PTR records; To make it a proper DNS zone, it handles SOA and NS queries for the apex of the zone.
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By default the apex of the zone will look like the following (assuming the zone used is `example.org`):
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~~~ dns
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example.org. 5 IN SOA ns1.dns.example.org. hostmaster.example.org. (
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12345 ; serial
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14400 ; refresh (4 hours)
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3600 ; retry (1 hour)
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604800 ; expire (1 week)
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5 ; minimum (4 hours)
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)
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example.org 5 IN NS ns1.dns.example.org.
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ns1.dns.example.org. 5 IN A ....
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ns1.dns.example.org. 5 IN AAAA ....
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~~~
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Note that we use the `dns` subdomain for the records DNS needs (see the `apex` directive). Also
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note the SOA's serial number is static. The IP addresses of the nameserver records are those of the
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CoreDNS service.
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The *k8s_external* plugin handles the subdomain `dns` and the apex of the zone itself; all other
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queries are resolved to addresses in the cluster.
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## Syntax
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~~~
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k8s_external [ZONE...]
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~~~
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* **ZONES** zones *k8s_external* should be authoritative for.
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If you want to change the apex domain or use a different TTL for the returned records you can use
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this extended syntax.
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~~~
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k8s_external [ZONE...] {
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apex APEX
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ttl TTL
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}
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~~~
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* **APEX** is the name (DNS label) to use for the apex records; it defaults to `dns`.
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* `ttl` allows you to set a custom **TTL** for responses. The default is 5 (seconds).
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If you want to enable headless service resolution, you can do so by adding `headless` option.
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~~~
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k8s_external [ZONE...] {
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headless
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}
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~~~
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* if there is a headless service with external IPs set, external IPs will be resolved
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If the queried domain does not exist, you can fall through to next plugin by adding the `fallthrough` option.
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~~~
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k8s_external [ZONE...] {
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fallthrough [ZONE...]
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}
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~~~
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## Examples
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Enable names under `example.org` to be resolved to in-cluster DNS addresses.
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~~~
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. {
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kubernetes cluster.local
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k8s_external example.org
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}
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~~~
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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`.
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~~~
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apiVersion: v1
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kind: Service
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metadata:
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name: test
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namespace: default
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spec:
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clusterIP: None
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externalIPs:
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- 192.168.200.123
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type: ClusterIP
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~~~
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The *k8s_external* plugin can be used in conjunction with the *transfer* plugin to enable
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zone transfers. Notifies are not supported.
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~~~
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. {
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transfer example.org {
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to *
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}
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kubernetes cluster.local
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k8s_external example.org
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}
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~~~
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With the `fallthrough` option, if the queried domain does not exist, it will be passed to the next plugin that matches the zone.
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~~~
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. {
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kubernetes cluster.local
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k8s_external example.org {
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fallthrough
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}
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forward . 8.8.8.8
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}
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~~~
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# See Also
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For some background see [resolve external IP address](https://github.com/kubernetes/dns/issues/242).
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And [A records for services with Load Balancer IP](https://github.com/coredns/coredns/issues/1851).
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