Merge branch '3.4' into 4.2

* 3.4:
  [Encore] Added some comments about asset versioning and deployment

Author: javiereguiluz

frontend/encore/versioning.rst

@@ -68,6 +68,23 @@ like normal:
 
     <img src="{{ asset('build/images/logo.png') }}">
 
+Troubleshooting
+---------------
+
+Asset Versioning and Deployment
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When deploying a new version of your application, versioned assets will include
+a new hash, making the previous assets no longer available. This is usually not
+a problem when deploying applications using a rolling update, blue/green or
+symlink strategies.
+
+However, even when applying those techniques, there could be a lapse of time
+when some publicly/privately cached response requests the previous version of
+the assets. If your application can't afford to serve any broken asset, the best
+solution is to use a CDN (or custom made service) that keeps all the old assets
+cached for some time.
+
 Learn more
 ----------