feat: persistent user home documentation (#2822)

* feat: persistent user home documentation

Signed-off-by: dkwon17 <[email protected]>

* Update modules/administration-guide/pages/about-persistent-user-home.adoc

Co-authored-by: Jana Vrbkova <[email protected]>

* Update modules/administration-guide/pages/about-persistent-user-home.adoc

Co-authored-by: Jana Vrbkova <[email protected]>

* Update modules/administration-guide/pages/about-persistent-user-home.adoc

Co-authored-by: Jana Vrbkova <[email protected]>

* Update modules/administration-guide/pages/about-persistent-user-home.adoc

Co-authored-by: Jana Vrbkova <[email protected]>

* Update modules/administration-guide/pages/about-persistent-user-home.adoc

Co-authored-by: Jana Vrbkova <[email protected]>

* Update modules/administration-guide/pages/about-persistent-user-home.adoc

Co-authored-by: Jana Vrbkova <[email protected]>

* Update based on PR feedback

Signed-off-by: dkwon17 <[email protected]>

* Update stow version

Signed-off-by: dkwon17 <[email protected]>

* Update PR typo

Signed-off-by: dkwon17 <[email protected]>

---------

Signed-off-by: dkwon17 <[email protected]>
Co-authored-by: Jana Vrbkova <[email protected]>

modules/administration-guide/nav.adoc

@@ -79,6 +79,7 @@
 *** xref:configuring-storage-classes.adoc[]
 *** xref:configuring-the-storage-strategy.adoc[]
 *** xref:configuring-storage-sizes.adoc[]
+*** xref:about-persistent-user-home.adoc[]
 ** xref:configuring-dashboard.adoc[]
 *** xref:configuring-getting-started-samples.adoc[]
 *** xref:configuring-editors-definitions.adoc[]

modules/administration-guide/pages/about-persistent-user-home.adoc

@@ -0,0 +1,65 @@
+:_content-type: CONCEPT
+:description: About persistent user home
+:keywords: administration guide, about, {prod-id-short}, persistent, user, home
+:navtitle: Persistent user home
+:page-aliases:
+
+[id="about-persistent-user-home"]
+= Persistent user home
+
+
+{prod} provides a persistent home directory feature that allows each non-ephemeral workspace to have their `/home/user` directory be persisted across workspace restarts.
+You can enable this feature in the CheCluster by setting `spec.devEnvironments.persistUserHome.enabled` to `true`.
+
+For newly started workspaces, this feature creates a PVC mounted to the `/home/user` path of the tools container.
+In this documentation, a "tools container" will be used to refer to the first container in the devfile.
+This container is the container that includes the project source code by default.
+
+When the PVC is mounted for the first time, the persistent volume's content are empty and therefore must be populated with the `/home/user` directory content.
+
+By default, the `persistUserHome` feature creates an init container for each new workspace pod named `init-persistent-home`.
+This init container is created with the tools container image and is responsible for running a `stow` command to create symbolic links
+in the persistent volume to populate the `/home/user` directory.
+
+NOTE: For files that cannot be symbolically linked to the `/home/user` directory such as the `.viminfo` and `.bashrc` file, `cp` is used instead of `stow`.
+
+The primary function of the `stow` command is to run:
+[subs="+quotes,attributes"]
+----
+stow -t /home/user/ -d /home/tooling/ --no-folding
+----
+
+The command above creates symbolic links in `/home/user` for files and directories located in /home/tooling. This populates the persistent volume with symbolic links to the content in `/home/tooling`. As a result, it the `persistentUserHome` feature expects the tooling image to have its `/home/user/` content within `/home/tooling`.
+
+For example, if the tools container image contains files in the `home/tooling` directory such as `.config` and `.config-folder/another-file`, stow will create symbolic links in the persistent volume in the following manner:
+
+.Tools container with `persistUserHome` enabled
+image::persistent-user-home/tools-container-example.png[Persistent user home example scenario]
+
+The init container writes the output of the `stow` command to `/home/user/.stow.log` and will only run `stow` the first time the persistent volume is mounted to the workspace. 
+
+Using the `stow` command to populate `/home/user` content in the persistent volume provides two main advantages:
+
+. Creating symbolic links is faster and consumes less storage than creating copies of the `/home/user` directory content in the persistent volume. To put it differently, the persistent volume in this case contains symbolic links and not the actual files themselves.
+. If the tools image is updated with newer versions of existing binaries, configs, and files, the init container does not need to `stow` the new versions, as the existing symbolic links will link to the newer versions in `/home/tooling` already.
+
+NOTE: If the tooling image is updated with additional binaries or files, they won't be symbolically linked to the `/home/user` directory since the `stow` command won't be run again. In this case, the user must delete the `/home/user/.stow_completed` file and restart the workspace to rerun `stow`.
+
+.`persistUserHome` tools image requirements
+
+The `persistUserHome` depends on the tools image used for the workspace. By default {prod-short} uses the Universal Developer Image (UDI) for sample workspaces, which supports `persistUserHome` out of the box.
+
+If you are using a custom image, there are three requirements that should be met to support the `persistUserHome` feature.
+
+. The tools image should contain `stow` version >= 2.4.0.
+. The `$HOME` environment variable is set to `/home/user`.
+. In the tools image, the directory that is intended to contain the `/home/user` content is `/home/tooling`.
+
+Due to requirement three, the default UDI image for example adds the `/home/user` content to `/home/tooling` instead, and runs:
+
+[subs="+quotes,attributes"]
+----
+RUN stow -t /home/user/ -d /home/tooling/ --no-folding 
+----
+
+in the Dockerfile so that files in `/home/tooling` are accessible from `/home/user` even when not using the `persistUserHome` feature.

modules/administration-guide/pages/configuring-storage.adoc

@@ -14,4 +14,5 @@
 
 * xref:configuring-storage-classes.adoc[]
 * xref:configuring-the-storage-strategy.adoc[]
-* xref:configuring-storage-sizes.adoc[]
+* xref:configuring-storage-sizes.adoc[]
+* xref:about-persistent-user-home.adoc[]