Add docs preview setup guide (#423)

* Add docs preview setup guide

* Add some additional info

* Add external host

* Fix typo

* fix typo

* Fix link

* Fix code callout

* Fix typos

* Syntactic sugar

Author: reakaleek

docs/docset.yml

@@ -19,6 +19,7 @@ external_hosts:
   - checkvist.com
   - commonmark.org
   - github.io
+  - github.com
 exclude:
   - '_*.md'
 subs:
@@ -50,6 +51,7 @@ toc:
           - file: automated.md
           - file: tooling.md
           - file: mapping.md
+          - file: how-to-set-up-docs-previews.md
   - folder: configure
     children:
       - file: index.md

docs/migration/guide/how-to-set-up-docs-previews.md

@@ -0,0 +1,128 @@
+# How to set up docs previews
+
+This guide will help you set up docs previews for your GitHub repository.
+
+## GitHub Workflows
+
+The docs preview system consists of three GitHub Workflows:
+- [`docs-build.yml`](#build): **Build** the docs on a PR
+- [`docs-deploy.yml`](#deploy): **Deploy** the docs to our preview environment
+- [`docs-cleanup.yml`](#cleanup): **Cleanup** the docs after a PR is merged or closed
+
+
+### Build
+
+This workflow is triggered when a PR is opened. The underlying reusable workflow, builds the documentation and uploads it as an artifact.
+If the `path-pattern` input does not match any changes in the PR, the workflow will skip the build, but still set a green status check.
+This way you only build and deploy the docs when there are changes to the docs and you can still set it as a required status check.
+
+
+::::{dropdown} .github/workflows/docs-build.yml
+:open:
+
+```yaml
+---
+name: docs-build <1>
+
+on:
+  pull_request: ~
+
+jobs:
+  docs-preview:
+    uses: elastic/docs-builder/.github/workflows/preview-build.yml <2>
+    with:
+      path-pattern: docs/** <3>
+    permissions:
+      contents: read
+      pull-requests: read
+```
+
+1. The naming is important so that the `docs-deploy` workflow is triggered.
+2. This should be the path to your docs folder.
+3. Reusable workflow: [elastic/docs-builder/.github/workflows/preview-build.yml](https://github.com/elastic/docs-builder/blob/main/.github/workflows/preview-build.yml)
+
+
+::::
+
+### Deploy
+
+This workflow is triggered when the `docs-build` workflow is completed. The underlying reusable workflow, downloads the artifact and deploys the docs to our preview environment.
+
+
+::::{dropdown} .github/workflows/docs-deploy.yml
+:open:
+
+```yaml
+---
+name: docs-deploy
+
+on:
+  workflow_run:
+    workflows: 
+      - docs-build <1>
+    types:
+      - completed
+
+jobs:
+  docs-preview:
+    uses: elastic/docs-builder/.github/workflows/preview-deploy.yml <2>
+    permissions:
+      contents: none <3>
+      id-token: write
+      deployments: write
+      actions: read
+```
+1. The name of the previously mentioned `docs-build` workflow.
+2. Reusable workflow: [elastic/docs-builder/.github/workflows/preview-deploy.yml](https://github.com/elastic/docs-builder/blob/main/.github/workflows/preview-deploy.yml)
+3. No need to read the code.
+
+::::
+
+### Cleanup
+
+This workflow is triggered when a PR is either merged or closed. The underlying reusable workflow, deletes the docs from the preview environment.
+
+:::{note}
+We are aware of the security implications of using `pull_request_target` as described in [this blog post](https://securitylab.github.com/resources/github-actions-preventing-pwn-requests/).
+The workflow never checks out the code and doesn't use any user modifiable inputs (e.g. PR title). 
+:::
+
+::::{dropdown} .github/workflows/docs-cleanup.yml
+:open:
+```yaml
+---
+name: docs-cleanup
+
+on:
+  pull_request_target:
+    types:
+      - closed
+
+jobs:
+  docs-preview:
+    uses: elastic/docs-builder/.github/workflows/preview-cleanup.yml <1>
+    permissions:
+      contents: none <2>
+      id-token: write
+      deployments: write
+```
+
+1. Reusable workflow: [elastic/docs-builder/.github/workflows/preview-cleanup.yml](https://github.com/elastic/docs-builder/blob/main/.github/workflows/preview-cleanup.yml)
+2. No permissions to read content
+
+::::
+
+## Required Status Checks
+
+To ensure that the docs are always in a deployable state, we need to set up required status checks.
+
+In this case only the `docs-build` workflow is required, which will produce a status check named `docs-preview / build`.
+
+![docs-preview required status check](img/docs-preview-required-status-check.png)
+
+
+## Deployments
+
+If the `docs-build` workflow is successful, the `docs-deploy` workflow will create a deployment visible in the GitHub UI on your PR.
+
+![docs-preview deployment](img/docs-preview-deployment.png)