add redirects section to readme

website/README.md

@@ -73,7 +73,7 @@ There is currently a small bug with new page creation - if you create a new page
 
 To change the version of Packer displayed for download on the website, head over to `data/version.js` and change the number there. It's important to note that the version number must match a version that has been released and is live on `releases.hashicorp.com` -- if it does not, the website will be unable to fetch links to the binaries and will not compile. So this version number should be changed _only after a release_.
 
-### Displaying a Prerelease
+#### Displaying a Prerelease
 
 If there is a prerelease of any type that should be displayed on the downloads page, this can be done by editing `pages/downloads/index.jsx`. By default, the download component might look something like this:
 
@@ -110,6 +110,7 @@ A {{ release candidate }} for Packer {{ v1.0.0 }} is available! The release can
 
 You may customize the parameters in any way you'd like. To remove a prerelease from the website, simply delete the `prerelease` paremeter from the above component.
 
+
 ### Markdown Enhancements
 
 There are several custom markdown plugins that are available by default that enhance standard markdown to fit our use cases. This set of plugins introduces a couple instances of custom syntax, and a couple specific pitfalls that are not present by default with markdown, detailed below:
@@ -135,6 +136,58 @@ There are several custom markdown plugins that are available by default that enh
 
   ...while it perhaps would not be an improved user experience, no links would break because of it. The best approach is to **avoid changing headlines and inline code at the start of a list item**. If you must change one of these items, make sure to tag someone from the digital marketing development team on your pull request, they will help to ensure as much compatibility as possible.
 
+### Redirects
+
+This website structures URLs based on the filesystem layout. This means that if a file is moved, removed, or a folder is re-organized, links will break. If a path change is necessary, it can be mitigated using redirects.
+
+To add a redirect, head over to the `_redirects` file - the format is fairly simple. On the left is the current path, and on the right is the path that should be redirected to. It's important to note that if there are links to a `.html` version of a page, that must also be explicitly redirected. For example:
+
+```
+/foo       /bar
+/foo.html  /bar
+```
+
+This redirect rule will send all incoming links to `/foo` and `/foo.html` to `/bar`. For more details on the redirects file format, [check out the docs on netlify](https://docs.netlify.com/routing/redirects/rewrites-proxies).
+
+There are a couple important caveats with redirects. First, redirects are applied at the hosting layer, and therefore will not work by default in local dev mode. To test in local dev mode, you can use [`netlify dev`](https://www.netlify.com/products/dev/), or just push a commit and check using the deploy preview.
+
+Second, redirects do not apply to client-side navigation. By default, all links in the navigation and docs sidebar will navigate purely on the client side, which makes navigation through the docs significantly faster, especially for those with low-end devices and/or weak internet connections. In the future, we plan to convert all internal links within docs pages to behave this way as well. This means that if there is a link on this website to a given piece of content that has changed locations in some way, we need to also _directly change existing links to the content_. This way, if a user clicks a link that navigates on the client side, or if they hit the url directly and the page renders from the server side, either one will work perfectly.
+
+Let's look at an example. Say you have a page called `/docs/foo` which needs to be moved to `/docs/nested/foo`. Additionally, this is a page that has been around for a while and we know there are links into `/docs/foo.html` left over from our previous website structure. First, we move the page, then adjust the docs sidenav, in `data/docs-navigation.js`. Find the category the page is in, and move it into the appropriate subcategory. Next, we add to `_redirects` as such:
+
+```
+/foo       /nested/foo
+/foo.html  /nested/foo
+```
+
+Finally, we run a global search for internal links to `/foo`, and make sure to adjust them to be `/nested/foo` - this is to ensure that client-side navigation still works correctly. _Adding a redirect alone is not enough_.
+
+One more example - let's say that content is being moved to an external website. A common example is guides moving to `learn.hashicorp.com`. In this case, we take all the same steps, except that we need to make a different type of change to the `docs-navigation` file. If previously the structure looked like:
+
+```js
+{
+  category: 'docs',
+  content: [
+    'foo'
+  ]
+}
+```
+
+If we no longer want the link to be in the side nav, we can simply remove it. If we do still want the link in the side nav, but pointing to an external destnation, we need to slightly change the structure as such:
+
+```js
+{
+  category: 'docs',
+  content: [
+    { title: 'Foo Title', href: 'https://learn.hashicorp.com/vault/foo' }
+  ]
+}
+```
+
+As the majority of items in the side nav are internal links, the structure makes it as easy as possible to represent these links. This alternate syntax is the most concise manner than an external link can be represented. External links can be used anywhere within the docs sidenav.
+
+It's also worth noting that it is possible to do glob-based redirects, for example matching `/docs/*`, and you may see this pattern in the `_redirects` file. This type of redirect is much higher risk and the behavior is a bit more nuanced, so if you need to add a glob redirect, please reach out to the website maintainers and ask about it first.
+
 ### Deployment
 
 This website is hosted on Netlify and configured to automatically deploy anytime you push code to the `stable-website` branch. Any time a pull request is submitted that changes files within the `website` folder, a deployment preview will appear in the github checks which can be used to validate the way docs changes will look live. Deployments from `stable-website` will look and behave the same way as deployment previews.