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doc/development/README.md

@@ -160,6 +160,7 @@ See [database guidelines](database/index.md).
 - [Security Scanners](integrations/secure.md)
 - [Secure Partner Integration](integrations/secure_partner_integration.md)
 - [How to run Jenkins in development environment](integrations/jenkins.md)
+- [How to run local Codesandbox integration for Web IDE Live Preview](integrations/codesandbox.md)
 
 ## Testing guides
 

doc/development/integrations/codesandbox.md

+# Set up local Codesandbox development environment
+
+This guide walks through setting up a local [Codesandbox repository](https://github.com/codesandbox/codesandbox-client) and integrating it with a local GitLab instance. Codesandbox 
+is used to power the Web IDE's [Live Preview feature](../../user/project/web_ide/index.md#live-preview). Having a local Codesandbox setup is useful for debugging upstream issues or 
+creating upstream contributions like [this one](https://github.com/codesandbox/codesandbox-client/pull/5137).
+
+## Initial setup
+
+Before using Codesandbox with your local GitLab instance, you must:
+
+1. Enable HTTPS on your GDK. Codesandbox uses Service Workers that require `https`.
+   Follow the GDK [NGINX configuration instructions](https://gitlab.com/gitlab-org/gitlab-development-kit/-/blob/master/doc/howto/nginx.md) to enable HTTPS for GDK.
+1. Clone the [`codesandbox-client` project](https://github.com/codesandbox/codesandbox-client)
+   locally. If you plan on contributing upstream, you might want to fork and clone first.
+1. (Optional) Use correct `python` and `nodejs` versions. Otherwise, `yarn` may fail to
+   install or build some packages. If you're using `asdf` you can run the following commands:
+
+   ```shell
+   asdf local nodejs 10.14.2
+   asdf local python 2.7.18
+   ```
+
+1. Run the following commands in the `codesandbox-client` project checkout:
+
+   ```shell
+   # This might be necessary for the `prepublishOnly` job that is run later
+   yarn global add lerna
+
+   # Install packages
+   yarn
+   ```
+
+   You can run `yarn build:clean` to clean up the build assets.
+
+## Use local GitLab instance with local Codesandbox
+
+GitLab integrates with two parts of Codesandbox:
+
+- An NPM package called `smooshpack` (called `sandpack` in the `codesandbox-client` project).
+  This exposes an entrypoint for us to kick off Codesandbox's bundler.
+- A server that houses Codesandbox assets for bundling and previewing. This is hosted
+  on a separate server for security.
+
+Each time you want to run GitLab and Codesandbox together, you need to perform the
+steps in the following sections.
+
+### Use local `smooshpack` for GitLab
+
+GitLab usually satisfies its `smooshpack` dependency with a remote module, but we want
+to use a locally-built module. To build and use a local `smooshpack` module:
+
+1. In the `codesandbox-client` project directory, run:
+
+   ```shell
+   cd standalone-packages/sandpack
+   yarn link
+
+   # (Optional) you might want to start a development build
+   yarn run start
+   ```
+
+   Now, in the GitLab project, you can run `yarn link "smooshpack"`. `yarn` looks 
+   for `smooshpack` **on disk** as opposed to the one hosted remotely.
+
+1. In the `gitlab` project directory, run:
+
+   ```shell
+   # Remove and reinstall node_modules just to be safe
+   rm -rf node_modules
+   yarn install
+
+   # Use the "smooshpack" package on disk
+   yarn link "smooshpack"
+   ```
+
+### Fix possible GDK webpack problem
+
+`webpack` in GDK can fail to find packages inside a linked package. This step can help
+you avoid `webpack` breaking with messages saying that it can't resolve packages from
+`smooshpack/dist/sandpack.es5.js`.
+
+In the `codesandbox-client` project directory, run:
+
+```shell
+cd standalone-packages
+
+mkdir node_modules
+ln -s $PATH_TO_LOCAL_GITLAB/node_modules/core-js ./node_modules/core-js
+```
+
+### Start building codesandbox app assets
+
+In the `codesandbox-client` project directory:
+
+```shell
+cd packages/app
+
+yarn start:sandpack-sandbox
+```
+
+### Create HTTPS proxy for Codesandbox `sandpack` assets
+
+Because we need `https`, we need to create a proxy to the webpack server. We can use
+[`http-server`](https://www.npmjs.com/package/http-server), which can do this proxying
+out of the box:
+
+```shell
+npx http-server --proxy http://localhost:3000 -S -C $PATH_TO_CERT_PEM -K $PATH_TO_KEY_PEM -p 8044 -d false
+```
+
+### Update `bundler_url` setting in GitLab
+
+We need to update our `application_setting_implementation.rb` to point to the server that hosts the 
+Codesandbox `sandpack` assets. For instance, if these assets are hosted by a server at `https://sandpack.local:8044`:
+
+```patch
+diff --git a/app/models/application_setting_implementation.rb b/app/models/application_setting_implementation.rb
+index 6eed627b502..1824669e881 100644
+--- a/app/models/application_setting_implementation.rb
++++ b/app/models/application_setting_implementation.rb
+@@ -391,7 +391,7 @@ def static_objects_external_storage_enabled?
+   # This will eventually be configurable
+   # https://gitlab.com/gitlab-org/gitlab/issues/208161
+   def web_ide_clientside_preview_bundler_url
+-    'https://sandbox-prod.gitlab-static.net'
++    'https://sandpack.local:8044'
+   end
+ 
+   private
+
+```
+
+NOTE:
+You can apply this patch by copying it to your clipboard and running `pbpaste | git apply`.
+
+You'll might want to restart the GitLab Rails server after making this change:
+
+```shell
+gdk restart rails-web
+```