Merge pull request kubernetes#28096 from gjkim42/expanded-dns-config

Add ExpandedDNSConfig feature gate

content/en/docs/concepts/services-networking/dns-pod-service.md

@@ -310,6 +310,17 @@ search default.svc.cluster-domain.example svc.cluster-domain.example cluster-dom
 options ndots:5
 ```
 
+#### Expanded DNS Configuration
+
+{{< feature-state for_k8s_version="1.22" state="alpha" >}}
+
+By default, for Pod's DNS Config, Kubernetes allows at most 6 search domains and
+a list of search domains of up to 256 characters.
+
+If the feature gate `ExpandedDNSConfig` is enabled for the kube-apiserver and
+the kubelet, it is allowed for Kubernetes to have at most 32 search domains and
+a list of search domains of up to 2048 characters.
+
 ### Feature availability
 
 The availability of Pod DNS Config and DNS Policy "`None`" is shown as below.

content/en/docs/reference/command-line-tools-reference/feature-gates.md

@@ -113,6 +113,7 @@ different Kubernetes components.
 | `EphemeralContainers` | `false` | Alpha | 1.16 | |
 | `ExpandCSIVolumes` | `false` | Alpha | 1.14 | 1.15 |
 | `ExpandCSIVolumes` | `true` | Beta | 1.16 | |
+| `ExpandedDNSConfig` | `false` | Alpha | 1.22 | |
 | `ExpandInUsePersistentVolumes` | `false` | Alpha | 1.11 | 1.14 |
 | `ExpandInUsePersistentVolumes` | `true` | Beta | 1.15 | |
 | `ExpandPersistentVolumes` | `false` | Alpha | 1.8 | 1.10 |
@@ -632,6 +633,9 @@ Each feature gate is designed for enabling/disabling a specific feature:
   now-corrected fault where Kubernetes ignored exec probe timeouts. See
   [readiness probes](/docs/tasks/configure-pod-container/configure-liveness-readiness-startup-probes/#configure-probes).
 - `ExpandCSIVolumes`: Enable the expanding of CSI volumes.
+- `ExpandedDNSConfig`: Enable kubelet and kube-apiserver to allow more DNS
+  search paths and longer list of DNS search paths. See
+  [Expanded DNS Configuration](/docs/concepts/services-networking/dns-pod-service/#expanded-dns-configuration).
 - `ExpandInUsePersistentVolumes`: Enable expanding in-use PVCs. See
   [Resizing an in-use PersistentVolumeClaim](/docs/concepts/storage/persistent-volumes/#resizing-an-in-use-persistentvolumeclaim).
 - `ExpandPersistentVolumes`: Enable the expanding of persistent volumes. See

content/en/docs/tasks/administer-cluster/dns-debugging-resolution.md

@@ -288,6 +288,13 @@ This should probably be implemented eventually.
 
 Linux's libc (a.k.a. glibc) has a limit for the DNS `nameserver` records to 3 by default. What's more, for the glibc versions which are older than glibc-2.17-222 ([the new versions update see this issue](https://access.redhat.com/solutions/58028)), the allowed number of DNS `search` records has been limited to 6 ([see this bug from 2005](https://bugzilla.redhat.com/show_bug.cgi?id=168253)). Kubernetes needs to consume 1 `nameserver` record and 3 `search` records. This means that if a local installation already uses 3 `nameserver`s or uses more than 3 `search`es while your glibc version is in the affected list, some of those settings will be lost. To work around the DNS `nameserver` records limit, the node can run `dnsmasq`, which will provide more `nameserver` entries. You can also use kubelet's `--resolv-conf` flag. To fix the DNS `search` records limit, consider upgrading your linux distribution or upgrading to an unaffected version of glibc.
 
+{{< note >}}
+
+With [Expanded DNS Configuration](/docs/concepts/services-networking/dns-pod-service/#expanded-dns-configuration),
+Kubernetes allows more DNS `search` records.
+
+{{< /note >}}
+
 If you are using Alpine version 3.3 or earlier as your base image, DNS may not
 work properly due to a known issue with Alpine.
 Kubernetes [issue 30215](https://github.com/kubernetes/kubernetes/issues/30215)