kubernetes
/
website
mirror of https://github.com/kubernetes/website.git
1
0
Fork 0
Code Issues Projects Releases Wiki Activity

Merge pull request #35923 from tengqm/tweak-dns-customization 

Tweak DNS customization page
pull/36962/head^2
Kubernetes Prow Robot 2022-09-23 19:36:03 -07:00 committed by GitHub
parent 242cfe1550 1edd6fd2b8
commit da18b430a0
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 59 additions and 112 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

171
content/en/docs/tasks/administer-cluster/dns-custom-nameservers.md
View File

@ -17,8 +17,6 @@ DNS resolution process in your cluster.
{{< include "task-tutorial-prereqs.md" >}}
Your cluster must be running the CoreDNS add-on.
[Migrating to CoreDNS](/docs/tasks/administer-cluster/coredns/#migrating-to-coredns)
explains how to use `kubeadm` to migrate from `kube-dns`.
{{% version-check %}}
@ -27,25 +25,27 @@ explains how to use `kubeadm` to migrate from `kube-dns`.
## Introduction
DNS is a built-in Kubernetes service launched automatically
using the _addon manager_
[cluster add-on](http://releases.k8s.io/master/cluster/addons/README.md).
As of Kubernetes v1.12, CoreDNS is the recommended DNS Server, replacing kube-dns. If your cluster
originally used kube-dns, you may still have `kube-dns` deployed rather than CoreDNS.
using the _addon manager_ [cluster add-on](http://releases.k8s.io/master/cluster/addons/README.md).
{{< note >}}
The CoreDNS Service is named `kube-dns` in the `metadata.name` field.
This is so that there is greater interoperability with workloads that relied on the legacy `kube-dns` Service name to resolve addresses internal to the cluster. Using a Service named `kube-dns` abstracts away the implementation detail of which DNS provider is running behind that common name.
The intent is to ensure greater interoperability with workloads that relied on
the legacy `kube-dns` Service name to resolve addresses internal to the cluster.
Using a Service named `kube-dns` abstracts away the implementation detail of
which DNS provider is running behind that common name.
{{< /note >}}
If you are running CoreDNS as a Deployment, it will typically be exposed as a Kubernetes Service with a static IP address.
The kubelet passes DNS resolver information to each container with the `--cluster-dns=<dns-service-ip>` flag.
If you are running CoreDNS as a Deployment, it will typically be exposed as
a Kubernetes Service with a static IP address.
The kubelet passes DNS resolver information to each container with the
`--cluster-dns=<dns-service-ip>` flag.
DNS names also need domains. You configure the local domain in the kubelet
with the flag `--cluster-domain=<default-local-domain>`.
The DNS server supports forward lookups (A and AAAA records), port lookups (SRV records), reverse IP address lookups (PTR records),
and more. For more information, see [DNS for Services and Pods](/docs/concepts/services-networking/dns-pod-service/).
The DNS server supports forward lookups (A and AAAA records), port lookups (SRV records),
reverse IP address lookups (PTR records), and more. For more information, see
[DNS for Services and Pods](/docs/concepts/services-networking/dns-pod-service/).
If a Pod's `dnsPolicy` is set to `default`, it inherits the name resolution
configuration from the node that the Pod runs on. The Pod's DNS resolution
@ -59,15 +59,16 @@ inheriting DNS. Set it to a valid file path to specify a file other than
## CoreDNS
CoreDNS is a general-purpose authoritative DNS server that can serve as cluster DNS, complying with the [dns specifications](https://github.com/kubernetes/dns/blob/master/docs/specification.md).
CoreDNS is a general-purpose authoritative DNS server that can serve as cluster DNS,
complying with the [DNS specifications](https://github.com/kubernetes/dns/blob/master/docs/specification.md).
### CoreDNS ConfigMap options
CoreDNS is a DNS server that is modular and pluggable, and each plugin adds new functionality to CoreDNS.
This can be configured by maintaining a [Corefile](https://coredns.io/2017/07/23/corefile-explained/), which is the CoreDNS
configuration file. As a cluster administrator, you can modify the
{{< glossary_tooltip text="ConfigMap" term_id="configmap" >}} for the CoreDNS Corefile to change how DNS service discovery
behaves for that cluster.
CoreDNS is a DNS server that is modular and pluggable, with plugins adding new functionalities.
The CoreDNS server can be configured by maintaining a [Corefile](https://coredns.io/2017/07/23/corefile-explained/),
which is the CoreDNS configuration file. As a cluster administrator, you can modify the
{{< glossary_tooltip text="ConfigMap" term_id="configmap" >}} for the CoreDNS Corefile to
change how DNS service discovery behaves for that cluster.
In Kubernetes, CoreDNS is installed with the following default Corefile configuration:
@ -102,35 +103,57 @@ data:
The Corefile configuration includes the following [plugins](https://coredns.io/plugins/) of CoreDNS:
* [errors](https://coredns.io/plugins/errors/): Errors are logged to stdout.
* [health](https://coredns.io/plugins/health/): Health of CoreDNS is reported to `http://localhost:8080/health`. In this extended syntax `lameduck` will make the process unhealthy then wait for 5 seconds before the process is shut down.
* [ready](https://coredns.io/plugins/ready/): An HTTP endpoint on port 8181 will return 200 OK, when all plugins that are able to signal readiness have done so.
* [kubernetes](https://coredns.io/plugins/kubernetes/): CoreDNS will reply to DNS queries based on IP of the services and pods of Kubernetes. You can find [more details](https://coredns.io/plugins/kubernetes/) about that plugin on the CoreDNS website. `ttl` allows you to set a custom TTL for responses. The default is 5 seconds. The minimum TTL allowed is 0 seconds, and the maximum is capped at 3600 seconds. Setting TTL to 0 will prevent records from being cached.
The `pods insecure` option is provided for backward compatibility with _kube-dns_. You can use the `pods verified` option, which returns an A record only if there exists a pod in same namespace with matching IP. The `pods disabled` option can be used if you don't use pod records.
* [prometheus](https://coredns.io/plugins/metrics/): Metrics of CoreDNS are available at `http://localhost:9153/metrics` in [Prometheus](https://prometheus.io/) format (also known as OpenMetrics).
* [forward](https://coredns.io/plugins/forward/): Any queries that are not within the cluster domain of Kubernetes will be forwarded to predefined resolvers (/etc/resolv.conf).
* [health](https://coredns.io/plugins/health/): Health of CoreDNS is reported to
`http://localhost:8080/health`. In this extended syntax `lameduck` will make theuprocess
unhealthy then wait for 5 seconds before the process is shut down.
* [ready](https://coredns.io/plugins/ready/): An HTTP endpoint on port 8181 will return 200 OK,
when all plugins that are able to signal readiness have done so.
* [kubernetes](https://coredns.io/plugins/kubernetes/): CoreDNS will reply to DNS queries
based on IP of the Services and Pods. You can find [more details](https://coredns.io/plugins/kubernetes/)
about this plugin on the CoreDNS website.
- `ttl` allows you to set a custom TTL for responses. The default is 5 seconds.
The minimum TTL allowed is 0 seconds, and the maximum is capped at 3600 seconds.
Setting TTL to 0 will prevent records from being cached.
- The `pods insecure` option is provided for backward compatibility with `kube-dns`.
- You can use the `pods verified` option, which returns an A record only if there exists a pod
in the same namespace with a matching IP.
- The `pods disabled` option can be used if you don't use pod records.
* [prometheus](https://coredns.io/plugins/metrics/): Metrics of CoreDNS are available at
`http://localhost:9153/metrics` in the [Prometheus](https://prometheus.io/) format
(also known as OpenMetrics).
* [forward](https://coredns.io/plugins/forward/): Any queries that are not within the Kubernetes
cluster domain are forwarded to predefined resolvers (/etc/resolv.conf).
* [cache](https://coredns.io/plugins/cache/): This enables a frontend cache.
* [loop](https://coredns.io/plugins/loop/): Detects simple forwarding loops and halts the CoreDNS process if a loop is found.
* [reload](https://coredns.io/plugins/reload): Allows automatic reload of a changed Corefile. After you edit the ConfigMap configuration, allow two minutes for your changes to take effect.
* [loadbalance](https://coredns.io/plugins/loadbalance): This is a round-robin DNS loadbalancer that randomizes the order of A, AAAA, and MX records in the answer.
* [loop](https://coredns.io/plugins/loop/): Detects simple forwarding loops and
halts the CoreDNS process if a loop is found.
* [reload](https://coredns.io/plugins/reload): Allows automatic reload of a changed Corefile.
After you edit the ConfigMap configuration, allow two minutes for your changes to take effect.
* [loadbalance](https://coredns.io/plugins/loadbalance): This is a round-robin DNS loadbalancer
that randomizes the order of A, AAAA, and MX records in the answer.
You can modify the default CoreDNS behavior by modifying the ConfigMap.
### Configuration of Stub-domain and upstream nameserver using CoreDNS
CoreDNS has the ability to configure stubdomains and upstream nameservers using the [forward plugin](https://coredns.io/plugins/forward/).
CoreDNS has the ability to configure stub-domains and upstream nameservers
using the [forward plugin](https://coredns.io/plugins/forward/).
#### Example
If a cluster operator has a [Consul](https://www.consul.io/) domain server located at 10.150.0.1, and all Consul names have the suffix .consul.local. To configure it in CoreDNS, the cluster administrator creates the following stanza in the CoreDNS ConfigMap.
If a cluster operator has a [Consul](https://www.consul.io/) domain server located at "10.150.0.1",
and all Consul names have the suffix ".consul.local". To configure it in CoreDNS,
the cluster administrator creates the following stanza in the CoreDNS ConfigMap.
```
consul.local:53 {
errors
cache 30
forward . 10.150.0.1
}
errors
cache 30
forward . 10.150.0.1
}
```
To explicitly force all non-cluster DNS lookups to go through a specific nameserver at 172.16.0.1, point the `forward` to the nameserver instead of `/etc/resolv.conf`
To explicitly force all non-cluster DNS lookups to go through a specific nameserver at 172.16.0.1,
point the `forward` to the nameserver instead of `/etc/resolv.conf`
```
forward . 172.16.0.1
@ -167,88 +190,12 @@ data:
}
```
The `kubeadm` tool supports automatic translation from the kube-dns ConfigMap
to the equivalent CoreDNS ConfigMap.
{{< note >}}
While kube-dns accepts an FQDN for stubdomain and nameserver (eg: ns.foo.com), CoreDNS does not support this feature.
CoreDNS does not support FQDNs for stub-domains and nameservers (eg: "ns.foo.com").
During translation, all FQDN nameservers will be omitted from the CoreDNS config.
{{< /note >}}
## CoreDNS configuration equivalent to kube-dns
CoreDNS supports the features of kube-dns and more.
A ConfigMap created for kube-dns to support `StubDomains`and `upstreamNameservers` translates to the `forward` plugin in CoreDNS.
### Example
This example ConfigMap for kube-dns specifies stubdomains and upstreamnameservers:
```yaml
apiVersion: v1
data:
stubDomains: |
{"abc.com" : ["1.2.3.4"], "my.cluster.local" : ["2.3.4.5"]}
upstreamNameservers: |
["8.8.8.8", "8.8.4.4"]
kind: ConfigMap
```
The equivalent configuration in CoreDNS creates a Corefile:
* For stubDomains:
```yaml
abc.com:53 {
errors
cache 30
forward . 1.2.3.4
}
my.cluster.local:53 {
errors
cache 30
forward . 2.3.4.5
}
```
The complete Corefile with the default plugins:
```
.:53 {
errors
health
kubernetes cluster.local in-addr.arpa ip6.arpa {
pods insecure
fallthrough in-addr.arpa ip6.arpa
}
federation cluster.local {
foo foo.feddomain.com
}
prometheus :9153
forward . 8.8.8.8 8.8.4.4
cache 30
}
abc.com:53 {
errors
cache 30
forward . 1.2.3.4
}
my.cluster.local:53 {
errors
cache 30
forward . 2.3.4.5
}
```
## Migration to CoreDNS
To migrate from kube-dns to CoreDNS, a detailed
[blog article](https://coredns.io/2018/05/21/migration-from-kube-dns-to-coredns/)
is available to help users adapt CoreDNS in place of kube-dns.
You can also migrate using the official CoreDNS
[deploy script](https://github.com/coredns/deployment/blob/master/kubernetes/deploy.sh).
## {{% heading "whatsnext" %}}
- Read [Debugging DNS Resolution](/docs/tasks/administer-cluster/dns-debugging-resolution/)