Doc: Tunneling Jupyter (#3841)

* Doc: Tunneling Jupyter

Document how to tunnel Jupyter servers.

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* Add explicit headless command to workflow

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Docs/source/dataanalysis/workflows.rst

@@ -0,0 +1,11 @@
+.. _dataanalysis-workflows:
+
+Workflows
+=========
+
+This section collects typical user workflows and best practices for data analysis with WarpX.
+
+.. toctree::
+   :maxdepth: 1
+
+   workflows/tunneling

Docs/source/dataanalysis/workflows/tunneling.rst

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+.. _dataanalysis-workflows-tunneling:
+
+Port Tunneling
+==============
+
+SSH port tunneling (port forwarding) is a secure way to access a computational service of a remote computer.
+A typical workflow where you might need port tunneling is for Jupyter data analysis, e.g., when analyzing data on your desktop computer but working from your laptop.
+
+Before getting started here, please note that many HPC centers offer a pre-installed Jupyter service, where tunnel is **not** needed.
+For example, see the :ref:`NERSC Jupyter <post-processing-perlmutter>` and :ref:`OLCF Jupyter <post-processing-frontier>` services.
+
+
+.. _dataanalysis-workflows-tunneling-background:
+
+Introduction
+------------
+
+When running a service such as Jupyter from your command line, it will start a local (web) port.
+The IPv4 address of your local computer is always ``127.0.0.1`` or the alias ``localhost``.
+
+As a secure default, you cannot connect from outside your local computer to this port.
+This prevents misconfigurations where one could, in the worst case, connect to your open port without authentication and execute commands with your user privileges.
+
+One way to access your remote Jupyter desktop service from your laptop is to forward the port started remotely via an encrypted SSH connection to a local port on your current laptop.
+The following section will explain the detailed workflow.
+
+
+.. _dataanalysis-workflows-tunneling-workflow:
+
+Workflow
+--------
+
+* you connect via SSH to your desktop at work, in a terminal (A) as usual
+
+  * e.g., ssh ``username@your-computers-hostname.dhcp.lbl.gov``
+  * start Jupyter locally in headless mode, e.g., ``jupyter lab --no-browser``
+  * this will show you a ``127.0.0.1`` (aka ``localhost``) URL, by default on port TCP ``8888``
+  * you cannot reach that URL, because you are not sitting on that computer, with your browser
+* You now start a second terminal (B) locally, which forwards  the remote port 8888 to your local laptop
+
+  * this step must be done **after** Jupyter was started on the desktop
+  * ``ssh -L <laptop-port>:<Ip-as-seen-on-desktop>:<desktop-port> <desktop-ip> -N``
+  * so concrete: ``ssh -L 8888:localhost:8888 your-computers-hostname.dhcp.lbl.gov -N``
+
+    * note: Jupyter on the desktop will increase the port if already in use.
+    * note: take another port on your laptop if you have local Jupyter instances still running
+* Now open the browser on your local laptop, open the URL from Jupyter with ``.../127.0.0.1:8888/...`` in it
+
+To close the connection down, do this:
+
+  * stop Jupyter in terminal A: ``Ctrl+C`` and confirm with ``y``, ``Enter``
+  * ``Ctrl+C`` the SSH tunnel in terminal B
+
+.. figure:: https://user-images.githubusercontent.com/1353258/232120440-3965fa38-9ca6-4621-a100-2da74eb899cf.png
+   :alt: Example view of remote started Jupyter service, active SSH tunnel, and local browser connecting to the service.
+   :width: 100%

Docs/source/index.rst

@@ -99,6 +99,7 @@ Data Analysis
    dataanalysis/visualpic
    dataanalysis/picviewer
    dataanalysis/reduced_diags
+   dataanalysis/workflows
 
 Theory
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