document --features (#2511)

Signed-off-by: Ashish Amarnath <ashisham@vmware.com>

site/docs/master/csi.md

@@ -8,7 +8,7 @@ The following are the prerequisites for using Velero to take Container Storage I
 
  1. The cluster is Kubernetes version 1.17 or greater.
  1. The cluster is running a CSI driver capable of support volume snapshots at the [v1beta1 API level](https://kubernetes.io/blog/2019/12/09/kubernetes-1-17-feature-cis-volume-snapshot-beta/).
- 1. The Velero server is running with the `--features EnableCSI` feature flag to enable CSI logic in Velero's core.
+ 1. The Velero server is running with the `--features EnableCSI` feature flag to enable CSI logic in Velero's core. See [Enabling Features][1] for more information.
  1. The Velero [CSI plugin](https://github.com/vmware-tanzu/velero-plugin-for-csi/) is installed to integrate with the CSI volume snapshot APIs.
  1. When restoring CSI volumesnapshots across clusters, the name of the CSI driver in the destination cluster is the same as that on the source cluster to ensure cross cluster portability of CSI volumesnapshots
 
@@ -27,3 +27,6 @@ This section documents some of the choices made during implementation of the Vel
 
 Velero's support level for CSI volume snapshotting will follow upstream Kubernetes support for it, and will reach general availability sometime
 after volume snapshotting is GA in upstream Kubernetes. Beta support is expected to launch in Velero v1.4.
+
+
+[1]: customize-installation.md#enable-server-side-features

site/docs/master/customize-installation.md

@@ -5,6 +5,9 @@
   - [Install in any namespace](#install-in-any-namespace)
   - [Use non-file-based identity mechanisms](#use-non-file-based-identity-mechanisms)
   - [Enable restic integration](#enable-restic-integration)
+  - [Enable features](#enable-features)
+    - [Enable server side features](#enable-server-side-features)
+    - [Enable client side features](#enable-client-side-features)
   - [Customize resource requests and limits](#customize-resource-requests-and-limits)
   - [Configure more than one storage location for backups or volume snapshots](#configure-more-than-one-storage-location-for-backups-or-volume-snapshots)
   - [Do not configure a backup storage location during install](#do-not-configure-a-backup-storage-location-during-install)
@@ -42,6 +45,45 @@ By default, `velero install` does not install Velero's [restic integration][3].
 
 If you've already run `velero install` without the `--use-restic` flag, you can run the same command again, including the `--use-restic` flag, to add the restic integration to your existing install.
 
+## Enable features
+
+New features in Velero will be released as beta features behind feature flags which are not enabled by default. A full listing of Velero feature flags can be found [here][11].
+
+### Enable server side features
+
+Features on the Velero server can be enabled using the `--features` flag to the `velero install` command. This flag takes as value a comma separated list of feature flags to enable. As an example [CSI snapshotting of PVCs][10] can be enabled using `EnableCSI` feature flag in the `velero install` command as shown below:
+
+```bash
+velero install --features=EnableCSI
+```
+
+Feature flags, passed to `velero install` will be passed to the Velero deployment and also to the `restic` daemon set, if `--use-restic` flag is used.
+
+Similarly, features may be disabled by removing the corresponding feature flags from the `--features` flag.
+
+Enabling and disabling feature flags will require modifying the Velero deployment and also the restic daemonset. This may be done from the CLI by uninstalling and re-installing Velero, or by editing the `deploy/velero` and `daemonset/restic` resources in-cluster.
+
+```bash
+$ kubectl -n velero edit deploy/velero
+$ kubectl -n velero edit daemonset/restic
+```
+
+### Enable client side features
+
+For some features it may be necessary to use the `--features` flag to the Velero client. This may be done by passing the `--features` on every command run using the Velero CLI or the by setting the features in the velero client config file using the `velero client config set` command as shown below:
+
+```bash
+velero client config set features=EnableCSI
+```
+
+This stores the config in a file at `$HOME/.config/velero/config.json`.
+
+All client side feature flags may be disabled using the below command
+
+```bash
+velero client config set features=
+```
+
 ## Customize resource requests and limits
 
 By default, the Velero deployment requests 500m CPU, 128Mi memory and sets a limit of 1000m CPU, 256Mi.
@@ -252,3 +294,5 @@ If you get an error like `complete:13: command not found: compdef`, then add the
 [7]: https://github.com/vmware-tanzu/velero/issues/2077
 [8]: https://github.com/vmware-tanzu/velero/issues/2311
 [9]: self-signed-certificates.md
+[10]: csi.md
+[11]: https://github.com/vmware-tanzu/velero/blob/master/pkg/apis/velero/v1/constants.go