Add docs for Gitlab Pages Redirects

Redirects feature added in https://gitlab.com/gitlab-org/gitlab-pages/-/merge_requests/336

doc/.vale/gitlab/spelling-exceptions.txt

@@ -284,6 +284,7 @@ namespaces
 namespacing
 namespacings
 Nanoc
+Netlify
 NGINX
 Nokogiri
 npm

doc/administration/pages/index.md

@@ -235,6 +235,7 @@ control over how the Pages daemon runs and serves content in your environment.
 | `pages_path` | The directory on disk where pages are stored, defaults to `GITLAB-RAILS/shared/pages`.
 | `pages_nginx[]` | |
 | `enable` | Include a virtual host `server{}` block for Pages inside NGINX. Needed for NGINX to proxy traffic back to the Pages daemon. Set to `false` if the Pages daemon should directly receive all requests, for example, when using [custom domains](index.md#custom-domains).
+| `FF_ENABLE_REDIRECTS` | Feature flag to enable redirects. See the [redirects documentation](../../user/project/pages/redirects.md#enable-or-disable-redirects) for more info. |
 
 ---
 
@@ -424,6 +425,10 @@ Authority (CA) in the system certificate store.
 
 For Omnibus, this is fixed by [installing a custom CA in Omnibus GitLab](https://docs.gitlab.com/omnibus/settings/ssl.html#install-custom-public-certificates).
 
+## Enable redirects
+
+In GitLab Pages, you can [enable the redirects feature](../../user/project/pages/redirects.md#enable-or-disable-redirects) to configure rules to forward one URL to another using HTTP redirects.
+
 ## Activate verbose logging for daemon
 
 Verbose logging was [introduced](https://gitlab.com/gitlab-org/omnibus-gitlab/-/merge_requests/2533) in

doc/administration/pages/source.md

@@ -347,6 +347,10 @@ world. Custom domains and TLS are supported.
 1. Restart NGINX
 1. [Restart GitLab](../restart_gitlab.md#installations-from-source)
 
+## Enable redirects
+
+In GitLab Pages, you can [enable the redirects feature](../../user/project/pages/redirects.md#enable-or-disable-redirects) to configure rules to forward one URL to another using HTTP redirects.
+
 ## NGINX caveats
 
 NOTE: **Note:**

doc/user/project/pages/index.md

@@ -59,6 +59,7 @@ To update a GitLab Pages website:
 | [Explore GitLab Pages](introduction.md) | Requirements, technical aspects, specific GitLab CI/CD configuration options, Access Control, custom 404 pages, limitations, FAQ. |
 | [Custom domains and SSL/TLS Certificates](custom_domains_ssl_tls_certification/index.md) | Custom domains and subdomains, DNS records, and SSL/TLS certificates. |
 | [Let's Encrypt integration](custom_domains_ssl_tls_certification/lets_encrypt_integration.md) | Secure your Pages sites with Let's Encrypt certificates, which are automatically obtained and renewed by GitLab. |
+| [Redirects](redirects.md) | Set up HTTP redirects to forward one page to another. |
 
 Learn more and see examples:
 

doc/user/project/pages/introduction.md

@@ -60,14 +60,8 @@ If the case of `404.html`, there are different scenarios. For example:
 
 ## Redirects in GitLab Pages
 
-Since you cannot use any custom server configuration files, like `.htaccess` or
-any `.conf` file, if you want to redirect a page to another
-location, you can use the [HTTP meta refresh tag](https://en.wikipedia.org/wiki/Meta_refresh).
-
-Some static site generators provide plugins for that functionality so that you
-don't have to create and edit HTML files manually. For example, Jekyll has the
-[redirect-from plugin](https://github.com/jekyll/jekyll-redirect-from), Sphinx
-has the [sphinx-reredirects](https://gitlab.com/documatt/sphinx-reredirects) extension.
+You can configure redirects for your site using a `_redirects` file. To learn more, read
+the [redirects documentation](redirects.md).
 
 ## GitLab Pages Access Control **(CORE)**
 

doc/user/project/pages/redirects.md

+---
+stage: Release
+group: Release Management
+info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#designated-technical-writers
+---
+
+# Create redirects for GitLab Pages
+
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab-pages/-/issues/24) in GitLab Pages 1.25.0 and GitLab 13.4.
+> - It's [deployed behind a feature flag](#enable-or-disable-redirects), disabled by default.
+> - To use it in GitLab self-managed instances, ask a GitLab administrator to [enable it](#enable-or-disable-redirects).
+
+CAUTION: **Warning:**
+This feature might not be available to you. Check the **version history** note above for details.
+
+In GitLab Pages, you can [enable](#enable-or-disable-redirects) the redirects feature to configure rules to forward one URL to another using HTTP redirects. GitLab Pages uses
+[Netlify style redirects](https://docs.netlify.com/routing/redirects/#syntax-for-the-redirects-file).
+
+## Supported features
+
+GitLab Pages only supports the
+[`_redirects` plain text file syntax](https://docs.netlify.com/routing/redirects/#syntax-for-the-redirects-file),
+and `.toml` files are not supported.
+
+Redirects are only supported at a basic level, and GitLab Pages doesn't support all
+[special options offered by Netlify](https://docs.netlify.com/routing/redirects/redirect-options/):
+
+| Feature | Supported | Example |
+| ------- | --------- | ------- |
+| Redirects (`301`, `302`) | **{check-circle}** Yes | `/wardrobe.html /narnia.html 302`
+| Rewrites (other status codes) | **{dotted-circle}** No | `/en/* /en/404.html 404` |
+| [Splats](https://docs.netlify.com/routing/redirects/redirect-options/#splats) | **{dotted-circle}** No | `/news/*  /blog/:splat` |
+| Placeholders | **{dotted-circle}** No | `/news/:year/:month/:date/:slug  /blog/:year/:month/:date/:slug` |
+| Query parameters | **{dotted-circle}** No | `/store id=:id  /blog/:id  301` |
+| Force ([shadowing](https://docs.netlify.com/routing/redirects/rewrites-proxies/#shadowing)) | **{dotted-circle}** No | `/app/  /app/index.html  200!` |
+| Domain-level redirects | **{dotted-circle}** No | `http://blog.example.com/* https://www.example.com/blog/:splat 301` |
+| Redirect by country or language | **{dotted-circle}** No | `/  /anz     302  Country=au,nz` |
+| Redirect by role | **{dotted-circle}** No | `/admin/*  200!  Role=admin` |
+
+NOTE: **Note:**
+Supported paths must start with a forward slash `/`.
+
+## Create redirects
+
+To create redirects after [enabling](#enable-or-disable-redirects) the feature,
+create a configuration file named `_redirects` in the `public/` directory of your
+GitLab Pages site.
+
+If your GitLab Pages site uses the default domain name (such as
+`namespace.gitlab.io/projectname`) you must prefix every rule with the project name:
+
+```plaintext
+/projectname/redirect-portal.html /projectname/magic-land.html 301
+/projectname/cake-portal.html /projectname/still-alive.html 302
+/projectname/wardrobe.html /projectname/narnia.html 302
+/projectname/pit.html /projectname/spikes.html 302
+```
+
+If your GitLab Pages site uses [custom domains](custom_domains_ssl_tls_certification/index.md),
+no project name prefix is needed. For example, if your custom domain is `example.com`,
+your `_redirect` file would look like:
+
+```plaintext
+/redirect-portal.html /magic-land.html 301
+/cake-portal.html /still-alive.html 302
+/wardrobe.html /narnia.html 302
+/pit.html /spikes.html 302
+```
+
+## Files override redirects
+
+Files take priority over redirects. If a file exists on disk, GitLab Pages serves
+the file instead of your redirect. For example, if the files `hello.html` and
+`world.html` exist, and the `_redirects` file contains the following line, the redirect
+is ignored because `hello.html` exists:
+
+```plaintext
+/projectname/hello.html /projectname/world.html 302
+```
+
+NOTE: **Note:**
+GitLab does not support Netlify's
+[force option](https://docs.netlify.com/routing/redirects/rewrites-proxies/#shadowing)
+to change this behavior.
+
+## Debug redirect rules
+
+If a redirect isn't working as expected, or you want to check your redirect syntax, visit
+`https://[namespace.gitlab.io]/projectname/_redirects`, replacing `[namespace.gitlab.io]` with
+your domain name. The `_redirects` file isn't served directly, but your browser
+displays a numbered list of your redirect rules, and whether the rule is valid or invalid:
+
+```plaintext
+11 rules
+rule 1: valid
+rule 2: valid
+rule 3: error: splats are not supported
+rule 4: valid
+rule 5: error: placeholders are not supported
+rule 6: valid
+rule 7: error: no domain-level redirects to outside sites
+rule 8: error: url path must start with forward slash /
+rule 9: error: no domain-level redirects to outside sites
+rule 10: valid
+rule 11: valid
+```
+
+## Enable or disable redirects
+
+Redirects in GitLab Pages is under development and not ready for production use. It is
+deployed behind a feature flag that is **disabled by default**.
+
+For [Omnibus installations](../../../administration/pages/index.md), define the
+`FF_ENABLE_REDIRECTS` environment variable in the
+[global settings](../../../administration/pages/index.md#global-settings).
+Add the following line to `/etc/gitlab/gitlab.rb` and
+[reconfigure the instance](../../../administration/restart_gitlab.md#omnibus-gitlab-reconfigure).
+
+```ruby
+gitlab_pages['env']['FF_ENABLE_REDIRECTS'] = 'true'
+```
+
+For [source installations](../../../administration/pages/source.md), define the
+`FF_ENABLE_REDIRECTS` environment variable, then
+[restart GitLab](../../../administration/restart_gitlab.md#installations-from-source):
+
+```shell
+export FF_ENABLE_REDIRECTS="true"
+/path/to/pages/bin/gitlab-pages -config gitlab-pages.conf
+```