docs: add jetbrains offline mode config steps (#9388)

docs/ides/gateway.md

@@ -188,3 +188,151 @@ In networks that restrict access to the internet, you will need to leverage the
 JetBrains Client Installer to download and save the IDE clients locally. Please
 see the
 [JetBrains documentation for more information](https://www.jetbrains.com/help/idea/fully-offline-mode.html).
+
+### Configuration Steps
+
+The Coder team built a POC of the JetBrains Gateway Offline Mode solution. Here
+are the steps we took (and "gotchas"):
+
+### 1. Deploy the server and install the Client Downloader
+
+We deployed a simple Ubuntu VM and installed the JetBrains Client Downloader
+binary. Note that the server must be a Linux-based distribution.
+
+```shell
+wget https://download.jetbrains.com/idea/code-with-me/backend/jetbrains-clients-downloader-linux-x86_64-1867.tar.gz && \
+tar -xzvf jetbrains-clients-downloader-linux-x86_64-1867.tar.gz
+```
+
+### 2. Install backends and clients
+
+JetBrains Gateway requires both a backend to be installed on the remote host
+(your Coder workspace) and a client to be installed on your local machine. You
+can host both on the server in this example.
+
+See here for the full
+[JetBrains product list and builds](https://data.services.jetbrains.com/products).
+Below is the full list of supported `--platforms-filter` values:
+
+```console
+windows-x64, windows-aarch64, linux-x64, linux-aarch64, osx-x64, osx-aarch64
+```
+
+To install both backends and clients, you will need to run two commands.
+
+**Backends**
+
+```shell
+./jetbrains-clients-downloader-linux-x86_64-1867/bin4/jetbrains-clients-downloader --products-filter <product-code> --build-filter <build-number> --platforms-filter linux-x64,windows-x64,osx-x64 --download-backends ~/backends
+```
+
+**Clients**
+
+This is the same command as above, with the `--download-backends` flag removed.
+
+```shell
+./jetbrains-clients-downloader-linux-x86_64-1867/bin4/jetbrains-clients-downloader --products-filter <product-code> --build-filter <build-number> --platforms-filter linux-x64,windows-x64,osx-x64 ~/clients
+```
+
+We now have both clients and backends installed.
+
+### 3. Install a web server
+
+You will need to run a web server in order to serve requests to the backend and
+client files. We installed `nginx` and setup an FQDN and routed all requests to
+`/`. See below:
+
+```console
+server {
+        listen 80 default_server;
+        listen [::]:80 default_server;
+
+        root /var/www/html;
+
+        index index.html index.htm index.nginx-debian.html;
+
+        server_name _;
+
+        location / {
+                root /home/ubuntu;
+        }
+}
+```
+
+Then, configure your DNS entry to point to the IP address of the server. For the
+purposes of the POC, we did not configure TLS, although that is a supported
+option.
+
+### 4. Add Client Files
+
+You will need to add the following files on your local machine in order for
+Gateway to pull the backend and client from the server.
+
+```shell
+$ cat productsInfoUrl # a path to products.json that was generated by the backend's downloader (it could be http://, https://, or file://)
+
+https://internal.site/backends/<PRODUCT_CODE>/products.json
+
+$ cat clientDownloadUrl # a path for clients that you got from the clients' downloader (it could be http://, https://, or file://)
+
+https://internal.site/clients/
+
+$ cat jreDownloadUrl # a path for JBR that you got from the clients' downloader (it could be http://, https://, or file://)
+
+https://internal.site/jre/
+
+$ cat pgpPublicKeyUrl # a URL to the KEYS file that was downloaded with the clients builds.
+
+https://internal.site/KEYS
+```
+
+The location of these files will depend upon your local operating system:
+
+**macOS**
+
+```console
+# User-specific settings
+/Users/UserName/Library/Application Support/JetBrains/RemoteDev
+# System-wide settings
+/Library/Application Support/JetBrains/RemoteDev/
+```
+
+**Linux**
+
+```console
+# User-specific settings
+$HOME/.config/JetBrains/RemoteDev
+# System-wide settings
+/etc/xdg/JetBrains/RemoteDev/
+```
+
+**Windows**
+
+```console
+# User-specific settings
+HKEY_CURRENT_USER registry
+# System-wide settings
+HKEY_LOCAL_MACHINE registry
+```
+
+Additionally, create a string for each setting with its appropriate value in
+`SOFTWARE\JetBrains\RemoteDev`:
+
+![Alt text](../images/gateway/jetbrains-offline-windows.png)
+
+### 5. Setup SSH connection with JetBrains Gateway
+
+With the server now configured, you can now configure your local machine to use
+Gateway. Here is the documentation to
+[setup SSH config via the Coder CLI](../ides.md#ssh-configuration). On the
+Gateway side, follow our guide here until step 16.
+
+Instead of downloading from jetbrains.com, we will point Gateway to our server
+endpoint. Select `Installation options...` and select `Use download link`. Note
+that the URL must explicitly reference the archive file:
+
+![Offline Gateway](../images/gateway/offline-gateway.png)
+
+Click `Download IDE and Connect`. Gateway should now download the backend and
+clients from the server into your remote workspace and local machine,
+respectively.