Add new page about Java tooling to dev section. Describe JRebel usage…

… including screenshot.

docs/development/index.rst

@@ -19,6 +19,7 @@ Please prepare your environment first:
 
     ./prepare
     ./mail
+    ./javatools
 
 
 

docs/development/javatools.rst

@@ -0,0 +1,69 @@
+======================
+Java Development Tools
+======================
+
+When developing with Java, you will want to use some tooling for deeper
+analysis of failures, hot-redeploys of the application, etc.
+
+Please step through the different tools below to learn how you can use them
+when using a (local) Kubernetes deployment as a part of your development
+workflow.
+
+These functionality is only enabled in the development flavors of :doc:`/images/dataverse-k8s`.
+You should not (and cannot) enable this in production.
+
+.. seealso:: If you need to swap out your production pod, take a look at `telepresence <https://www.telepresence.io/>`_.
+
+Metrics and Performance with VisualVM
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+
+
+Debugging with JDWP
+^^^^^^^^^^^^^^^^^^^
+
+
+
+Hot-Reploy of evolving parts with JRebel
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+On startup, when the environment variable ``ENABLE_JREBEL=1``, the application
+server is configured to enable JRebel support on deployment.
+
+You might set this variable in any way you like. On Kubernetes, the easiest way
+is likely to be via the Dataverse ``ConfigMap`` (see also :doc:`/day1/config`):
+
+.. code-block:: yaml
+
+  # [...]
+  data:
+    ENABLE_JREBEL: "1"
+
+Once your application server is up, JRebel communicates with the IDE extensions
+via the very same port that you use to access Dataverse in the browser. Please
+follow their instructions to configure your IDE plugin.
+
+Below is an example using IntelliJ IDEA and its JRebel Plugin, syncing via
+a ``kubectl port-forward`` from localhost into the cluster:
+
+.. thumbnail:: img/jrebel-idea.png
+  :title: JRebel in Dataverse Pod enabled in IntelliJ IDEA.
+
+.. danger::
+
+  You will need to raise the RAM limit of the pod when enabling this.
+  Dev default 1 GiB RAM is not sufficient, 1.5 GiB (= 750 MiB heap) is bare
+  minimum. You might need to add more RAM to your Kubernetes cluster, depending
+  on your setup.
+
+.. important::
+
+  Please be aware that you will need a JRebel license to use this timesaving
+  feature. Good products have a reasonable price. You have been warned.
+  https://www.jrebel.com/products/jrebel
+
+.. seealso::
+
+  In the future, when Dataverse runs on Java JDK 11, one might take a look at
+  http://hotswapagent.org. There are only outdated DCEVM patches for JDK 8,
+  so this is currently not an alternative.