New fast register instructions (flyteorg#678)

rsts/user/features/fast_registration.rst

@@ -9,10 +9,67 @@ Fast Registration
 Are you frustrated by having to wait for an image build in order to test out simple code changes to your Flyte workflows? If you're interested in reducing to your iteration cycle to mere seconds, read on below.
 
 Caveats
-#######
+=======
 
 Fast-registration only works when you're testing out code changes. If you need to update your container, say by installing a dependency or modifying a Dockerfile, you **must** use the conventional method of committing your changes and rebuilding a container image.
 
+Prerequisites
+=============
+
+* Upgrade your flytekit dependency to ``>=0.16.0`` and re-run piptools if necessary
+
+
+You'll need to build a base image with these changes incorporated before you can use fast registration.
+
+
+Fast-registering
+================
+
+How-to:
+
+* After the above prerequisite changes are merged, pull the latest master and create a development branch on your local machine.
+* Make some code changes. Save your files.
+* Clear and/or create the directory used to store your serialized code archive:
+
+.. code-block:: text 
+
+   mkdir _pb_output || true
+   rm -f _pb_output/*.tar.gz 
+
+* Using a python environment with flytekit installed fast-register your changes:
+
+.. code-block:: python 
+
+   pyflyte -c sandbox.config --pkgs recipes serialize --in-container-config-path /root/sandbox.config \
+       --local-source-root <path to your code> --image <older/existing docker image here> fast workflows -f _pb_output/
+ 
+
+Or, from within your container:
+
+ .. code-block:: python 
+
+    pyflyte --config /root/sandbox.config serialize fast workflows -f _pb_output/ 
+
+* Assume a role that has write access to the intermittent directory you'll use to store fast registration code distributions .
+* Fast-register your serialized files. You'll note the overlap with the existing register command (auth role and output location)
+   but with an new flag pointing to an additional distribution dir. This must be writable from the role you assume and readable from
+   the role your flytepropeller assumes:
+
+ .. code-block:: python 
+
+    flyte-cli fast-register-files -p flytetester -d development --kubernetes-service-account ${FLYTE_AUTH_KUBERNETES_SERVICE_ACCOUNT} \
+        --output-location-prefix ${FLYTE_AUTH_RAW_OUTPUT_DATA_PREFIX} -h ${FLYTE_PLATFORM_URL} \
+        --additional-distribution-dir ${FLYTE_SDK_FAST_REGISTRATION_DIR} _pb_output/*
+ 
+
+* Open the Flyte UI and launch the latest version of your workflow (under the domain you fast-registered above). It should run with your new code!
+
+
+Older flytekit instructions (flytekit <0.16.0)
+==============================================
+
+Flytekit releases prior to the introduction of native typing have a slightly modified workflow for fast-registering.
+
 Prerequisites
 #############