minor #11422 Encore: add guide to use Encore in a virtual machine (Kocal)

This PR was squashed before being merged into the 3.4 branch (closes #11422).

Discussion
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Encore: add guide to use Encore in a virtual machine

Hi, ✋

As the title says, this PR add a new guide for using Encore in a virtual machine.

This is what we use on ours Symfony apps at work which run inside a Vagrant VM.
It works really fine and I thought it would be helpful to share it with other people.

Also, I've removed a sub-section in the actual doc because according to symfony/webpack-encore#277, it was not working because some additional configuration was missing (and I can confirm it because I'm one of his co-worker 😛).

Commits
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86c897f Encore: add guide to use Encore in a virtual machine

Author: javiereguiluz

frontend.rst

@@ -74,6 +74,7 @@ Guides
 * :doc:`webpack-dev-server and Hot Module Replacement (HMR) </frontend/encore/dev-server>`
 * :doc:`Adding custom loaders & plugins </frontend/encore/custom-loaders-plugins>`
 * :doc:`Advanced Webpack Configuration </frontend/encore/advanced-config>`
+* :doc:`Using Encore in a Virtual Machine </frontend/encore/virtual-machine>`
 
 Issues & Questions
 ..................

frontend/encore/dev-server.rst

@@ -26,19 +26,6 @@ by the normal `webpack-dev-server`_. For example:
 
 This will start a server at ``https://localhost:9000``.
 
-Using dev-server inside a VM
-----------------------------
-
-If you're using ``dev-server`` from inside a virtual machine, then you'll need
-to bind to all IP addresses and allow any host to access the server:
-
-.. code-block:: terminal
-
-    $ ./node_modules/.bin/encore dev-server --host 0.0.0.0 --disable-host-check
-
-You can now access the dev-server using the IP address to your virtual machine on
-port 8080 - e.g. http://192.168.1.1:8080.
-
 Hot Module Replacement HMR
 --------------------------
 

frontend/encore/virtual-machine.rst

@@ -0,0 +1,112 @@
+Using Encore in a Virtual Machine
+=================================
+
+You may encounter some issues when using Encore in a virtual machine, like VirtualBox or VMWare.
+
+Fix watching issues
+-------------------
+
+When using a virtual machine, your project root directory is shared with the virtual machine with `NFS`_.
+This is really useful, but it introduces some issues with files watching.
+
+You must enable `polling`_ option to make it work:
+
+.. code-block:: javascript
+
+    // webpack.config.js
+
+    // ...
+
+    // will be applied for `encore dev --watch` and `encore dev-server` commands
+    Encore.configureWatchOptions(watchOptions => {
+        watchOptions.poll = 250; // check for changes every 250 ms
+    });
+
+Fix development server
+----------------------
+
+Configure public path
+~~~~~~~~~~~~~~~~~~~~~
+
+.. note::
+
+    You can skip this sub-section if your app is running on ``http://localhost``
+    and not a custom local domain-name like ``http://app.vm``.
+
+When running the development server, you will probably face the following errors in the web console:
+
+.. code-block:: text
+
+    GET http://localhost:8080/build/vendors~app.css net::ERR_CONNECTION_REFUSED
+    GET http://localhost:8080/build/runtime.js net::ERR_CONNECTION_REFUSED
+    ...
+
+If your Symfony application is running on ``http://app.vm``, you must configure the public path explicitly
+in your ``package.json``:
+
+.. code-block:: diff
+
+    {
+        ...
+        "scripts": {
+    -        "dev-server": "encore dev-server",
+    +        "dev-server": "encore dev-server --public http://app.vm:8080",
+            ...
+        }
+    }
+
+After restarting Encore and reloading your web page, you will probably face different issues:
+
+.. code-block:: text
+
+    GET http://app.vm:8080/build/vendors~app.css net::ERR_CONNECTION_REFUSED
+    GET http://app.vm:8080/build/runtime.js net::ERR_CONNECTION_REFUSED
+
+Encore understood our modification but it's still not working. There is still two things to do.
+
+Allow external access
+~~~~~~~~~~~~~~~~~~~~~
+
+You must configure how you run the `webpack-dev-server`_.
+This can easily be done in your ``package.json`` by adding ``--host 0.0.0.0`` argument:
+
+.. code-block:: diff
+
+    {
+        ...
+        "scripts": {
+    -        "dev-server": "encore dev-server --public http://app.vm:8080",
+    +        "dev-server": "encore dev-server --public http://app.vm:8080 --host 0.0.0.0",
+            ...
+        }
+    }
+
+.. warning::
+
+    Using ``--host 0.0.0.0`` makes your development server accept all incoming connections.
+    Be sure to run the development server inside your virtual machine and not outside, otherwise other computers can have access to it.
+
+Fix "Invalid Host header" issue
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Webpack will respond ``Invalid Host header`` when trying to access files from the dev-server.
+To fix this, add the argument ``--disable-host-check``:
+
+.. code-block:: diff
+
+    {
+        ...
+        "scripts": {
+    -        "dev-server": "encore dev-server --public http://app.vm:8080 --host 0.0.0.0",
+    +        "dev-server": "encore dev-server --public http://app.vm:8080 --host 0.0.0.0 --disable-host-check",
+            ...
+        }
+    }
+
+.. warning::
+
+    This is usually not recommended to disable host checking, `more information here <https://webpack.js.org/configuration/dev-server/#devserverdisablehostcheck>`_.
+
+.. _`NFS`: https://en.wikipedia.org/wiki/Network_File_System
+.. _`polling`: https://webpack.js.org/configuration/watch/#watchoptionspoll
+.. _`webpack-dev-server`: https://webpack.js.org/configuration/dev-server/